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Article

Evidence for Conductivity- and Macroinvertebrate-Driven Segregation of Ostracod Assemblages in Endorheic Depression Wetlands in North West Province of South Africa

by
Agata Szwarc
1,*,
Koen Martens
2,3,
Włodzimierz Meissner
4 and
Tadeusz Namiotko
1,*
1
Laboratory of Biosystematics and Ecology of Aquatic Invertebrates, Department of Evolutionary Genetics and Biosystematics, Faculty of Biology, University of Gdansk, Wita Stwosza 58, 80-308 Gdansk, Poland
2
Royal Belgian Institute of Natural Sciences (RBINS), Natural Environments, Freshwater Biology, Vautierstraat 29, 1000 Brussels, Belgium
3
Department of Biology, Ghent University, K.L. Ledeganckstraat 35, 9000 Ghent, Belgium
4
Ornithology Unit, Department of Vertebrate Ecology and Zoology, Faculty of Biology, University of Gdansk, Wita Stwosza 59, 80-308 Gdansk, Poland
*
Authors to whom correspondence should be addressed.
Diversity 2023, 15(5), 614; https://doi.org/10.3390/d15050614
Submission received: 28 February 2023 / Revised: 26 April 2023 / Accepted: 27 April 2023 / Published: 30 April 2023
(This article belongs to the Section Animal Diversity)
Browse Figures
Versions Notes

Abstract

:
Our knowledge of the ecology of non-marine Ostracoda inhabiting endorheic wetlands (pans) of the semi-arid regions of South Africa is very scarce. The present study investigates the distribution of ostracod species in grass, open, and salt pans in the central part of the North West province and tests ostracod response to abiotic and biotic predictor variables operating at a local scale. Distance-based linear models revealed three variables (pan type, water electrical conductivity and abundance of macroinvertebrate predators, and collector-gatherers) that best explained variation in the ostracod dataset. Ostracod assemblages from the three studied pan types differed by the dominance structure rather than by the species composition. Salt pans with high conductivity and high ratio of predaceous macroinvertebrates were dominated by Heterocypris giesbrechti, with accessory presence of Plesiocypridopsis newtoni. In open pans with low conductivities and the lowest ratio of predators (but highest ratio of collector-gatherers) Potamocypris mastigophora was typically a dominant species, while in grass pans, all the three mentioned species had similar relative abundances. Although our findings lend provisional support to some models of ostracod assemblage diversity across different pan types, more studies replicating endorheic depression wetlands in other regions are required before generalizations can be made.

1. Introduction

The term “wetlands” groups a wide range of variable habitats, ranging between (semi-)terrestrial and aquatic systems, and which are distributed worldwide. Various factors, such as their hydrological cycle (permanent or temporary), substrate type, salinity, vegetation, or location, allow to distinguish different types amongst them. Owing to the delicate balance between rainfall and evapotranspiration, these areas are highly vulnerable to climate change [1]. Temporary waters, which are the most common type of wetlands in arid regions, are defined by Williams [2] as bodies of fresh water that experience a recurrent dry phase of varying length, making them one of the most unpredictable and seemingly unsuitable habitats in the world. Despite the fact that such waterbodies, commonly known as “pans” in South Africa [3], represent a significant part of the global landscape and have huge importance for the preservation of biodiversity, they are under threat from global climate change and a wide range of human activities [4,5].
One type of temporary waters are endorheic pans, which are characterized by circular to oval, sometimes kidney-like shape and a flat basin floor and by the fact that they only have inflow and no outflow channels [6]. During the dry season, endorheic pans can be completely dry, even for several years, until rain fall in the drainage area fills up these depressions in the terrain. The existence of these ecosystems is therefore largely dependent on general climate and specific weather conditions. In such highly variable environments, external factors strongly affect the development of the inhabitants of such temporary wetlands [7]. Invertebrates living in temporary waters are mainly exposed to desiccation, variation in water chemistry, high and strongly fluctuating temperatures, low oxygen concentrations, high light and UV radiation intensities, variation in a range of other environmental factors and habitat isolation [8]. In order to survive, such organisms must adapt to unsuitable environmental conditions by the acquisition of different life history strategies, for example by undergoing diapause or producing resting and dormant stages [9,10]. By producing resting eggs, organisms can also disperse passively, which is an adaptation to rapid colonization of new waterbodies and also to survive periods of drought and to allow development after another flooding [11,12].
Nhiwatiwa and Dalu [13] suggested that physical and chemical properties of water in temporary ecosystems play a fundamental role in shaping their communities, much more so than in permanent systems. For example, rapid water loss by evaporation can cause high levels of salinity in many endorheic wetlands [14].
Various groups of invertebrates abound in temporary waters, and ostracod assemblages tend to be particularly common and species-rich [15,16]. This is especially so for species of the family Cyprididae Baird, 1845 [17] which are generally excellent swimmers and can also be relatively large (the South African temporary pool ostracod Megalocypris princeps Sars, 1898 can be up to 8 mm long). This “gigantism” is largely related to the absence of fish, which predate on ostracods, in such temporary and/or saline water bodies, although invertebrate predation can also be significant (see below). The Cyprididae are, with more than 40% of all known species, the largest family of living non-marine ostracods [18]. Most of these species are free-swimming, produce drought resistant stages, and can often reproduce parthenogenetically. These three biological traits make cypridid species excellent dispersers. Yet, only few species have a cosmopolitan distribution and most are restricted to one (sub-)continent [18]. Several geographical regions have high levels of local endemicity of ostracods, and southern Africa is a well-known example [19]. This suggests that local environmental conditions can have a strong impact on the composition of communities and assemblages [20,21].
Here, we aim to determine the taxonomic composition and dominance structure of ostracod assemblages and also to examine how abiotic and biotic environmental factors influence such assemblages in endorheic waters of the central part of the North West province in South Africa. The novelty of this study is to address the role of macroinvertebrates and their functional feeding groups on ostracod assemblage distribution patterns.

2. Materials and Methods

2.1. Study Area, Location, and Selection of the Sampling Sites

The study sites were situated in the highveld plain (elevation of ca. 1350 m) of the central part of the North West province of South Africa (Figure 1), between Delareyville and Deelpan, where numerous generally shallow and non-perennial wetlands of various sizes occur and function as important breeding and feeding habitats for waterfowl and for aquatic invertebrates [22,23], but also as watering holes for game and cattle. This mostly agricultural area of ca. 300 km2 belongs to an austral summer rainfall region located in a hot semi-arid zone which experiences erratic rainfall ranging from 360 to 560 mm per year, with the highest peak in January. The annual average temperature is 19–23 °C; however, extremely high monthly and daily temperature variation is typical for the area, with a minimum of around 0 °C in July and a maximum of 30 °C in January [23,24,25,26,27]; Ramsar Convention’s web site http://www.ramsar.org (accessed on 27 June 2022). As a result of high evaporation rates, reasonably high concentrations of salts occur in the soil, thus sediments of depressional wetlands tend to be alkaline [23,24].
The sampling sites were chosen to include a relatively wide range of environmental conditions (regarding pan type and size, water chemistry or land use and human impact in the immediate catchment) in a rather small spatial extent in order to minimize the influence of environmental or climatic processes, operating at a more regional scale, on aquatic invertebrate communities.
In total 20 sites were sampled during two surveys. During the first survey, on 8 September 2009, samples from four sites localized close to each other in the Godwit Bay of Barberspan (between 26°35′39″ S, 25°33′33″ E and 26°36′08″ S, 25°34′07″ E) were collected for a reconnaissance faunistic and taxonomic study.
The second survey (at the end of the rainy season between 31 March and 5 April 2011) on ostracod-environment associations investigated 16 sites (Table 1, Figure 1) of which 15 were endorheic depressional wetlands or pans of three types (classified according to [28]): grass (8 sites), open (3 sites), and salt pans (4 sites). The remaining site was an artificial trough holding water for sheep (indicated as “other” in multivariate analysis), and was included in the present study to test if its ostracod assemblages were similar to those found in the studied natural pans. Except large (surface of almost 20 km2 depending on the season) and perennial Barberspan, the other studied pans were temporary and reasonably small (<5 km2), as is the case for the majority of the pans in the North West province. Barberspan was originally also non-perennial but in 1918 water from the nearby Harts river was artificially diverted into Barberspan, changing the system into a permanent waterbody ([26] and Ramsar Convention’s web site http://www.ramsar.org (accessed on 27 June 2022)). The studied sites were located mostly in relatively unimpacted natural areas (12 sites) and represented principally small (9 sites of surface area <0.2 km2), temporary waterbodies devoid of fish (10 sites) with sandy or sandy-muddy substrate (12 sites) and rather overgrown with macrophytes (Table 1).

2.2. Sampling, Identification of Biota, and Environmental Characterization

Biotic (ostracods and accompanying invertebrates) semi-quantitative samples were collected using a hand-net (120 µm mesh size) from the bottom surface of ca. 0.5 m2 (wherever possible) at depths to max. 50 cm, and then rinsed and preserved in 96% ethanol. Ostracods were sorted, identified, and counted using a stereoscopic light-reflected microscope at up to 25× magnification and a light-transmitted microscope at up to 400× magnification. Empty valves were not included in later analyses. Soft parts of ostracods were studied after full dissection with needles in glycerine on glass slides and valves were stored dry in micropalaeontological slides. Carapaces and valves were also observed and illustrated using scanning electron microscopy (SEM). Ostracods were identified down to the species level using primarily the following taxonomic literature [19,29,30,31,32,33]. The names of the ostracod species, their authorities, and family assignments are allocated according to a recent checklist [18]. Other invertebrates were identified mostly to the family level using guides by [34,35,36,37,38,39,40,41,42,43]. To each macroinvertebrate taxon, a Functional Feeding Group (FFG) was assigned as described in [41,42,44,45,46,47,48,49] and/or in the general classification system for aquatic macroinvertebrate FFG by [50].
At each site, a set of environmental variables were measured or assessed, including water properties, sediment and vegetation characteristics, site geography, and urban proximity. Longitude, latitude, and altitude (m A.S.L.) were recorded using a MLR Electronique SP24XC GPS receiver. Electrical conductivity (μS cm−1) at 25 °C, pH, and surface water temperature (°C) were measured in situ using a hand-held multi-parameter probe WTW Multi 350i. Type of substrate was categorized visually according to the dominant grain size fraction into muddy, sandy-muddy, sandy, or artificial. We also noted the perceived influence of urban activities and differentiated between two main types of study sites: (1) urban or degraded sites when pans were situated adjacent to or surrounded by towns or villages, and (2) natural sites when pans were relatively unaffected by urban activities. Data on fish presence were taken from the literature [26] and/or validated by field observation and confirmed by local landowners and residents (fish can be assumed absent in isolated (not connected to rivers and streams), small, temporary pans). An assessment of the total macrophyte vegetation cover at the sampling site was made visually and scored using an arbitrary scale, where 0: 0–10% vegetation cover of the water surface, 1: 11–50% and 2: 51–100%. The size of the studied waterbodies was calculated using GPS data and scored using a scale from 1 to 3 (where 1: <0.2 km2, 2: 0.3–1.0 km2 and 3: 1.1–20 km2).

2.3. Linking Ostracod Assemblage Analysis to Environmental Variables

The ostracod data included relative abundances (percentages) of species found at 13 out of 16 sampling sites of the 2011 survey. All analyses were based on the Bray-Curtis sample similarity matrix and performed with PRIMER 7 software [51] with the PERMANOVA+ add-on package [52].
A shade plot was used to determine patterns of ostracod assemblage groupings and to illustrate the distribution of individual species across different pan types. In the shade plot, samples (constrained by the pan type) and species were independently placed in the nearest neighbor order using the “greedy traveling salesman algorithm” (for details see [51,53]), based for samples on Bray-Curtis similarities on percentages, whereas for species on the association index on species-standardized data. Differences in ostracod assemblage composition between the three pan types were tested by Analysis of Similarity (ANOSIM). The Similarity Percentage (SIMPER) procedure was performed to determine which ostracod species contributed the most to the similarity among sites within each pan type and to the dissimilarity between the three pan types. To test if similarities between ostracod assemblages at the study sites correlate with the geographical distance between the sites, the RELATE routine was used by calculating a rank correlation coefficient between all the sites of their respective (dis)similarity/distance matrices (an analogue technique to parametric Mantel test, see for details [51,53]).
To test the relationship between ostracod-derived response dataset and environmental predictor variables, the distance-based linear model (DistLM) was used with a modified Akaike Information Criterion corrected for small sample size (AICc) [52] as selection procedure and “Best” as selection criterion. Significance of individual environmental variables responsible for the ostracod multivariate data was checked by the marginal tests, while the best fitted DistLM model was visualized and interpreted through a two-dimensional ordination tri-plot using the distance-based redundancy analysis (dbRDA) with overlying vectors of both predicting environmental variables and response ostracod data.
We used in total 10 explanatory variables of various nature in attempting to explain the ostracod assemblage distribution patterns (four continuous variables, five semi-quantitative or ordinal variables and one categorical variable): 1. Water electrical conductivity (continuous variable transformed to reduce skewness); 2. Water pH (continuous variable); 3. Substrate type (ordinal variable with four categories: muddy, muddy-sandy, sandy and concrete); 4. Land use (or human impact) in the immediate catchment (ordinal variable with two categories: natural and urban sites); 5. Fish presence (ordinal variable with two categories: absence and presence); 6. Macrophyte vegetation coverage (ordinal variable with three categories: 0, 1 and 2, see above on the used arbitrary scale); 7. Waterbody surface area (ordinal variable with three categories: 1, 2, 3, see above); 8. Pan type (categorical variable with 4 categories: grass, open, salt and other for the non-pan site). Two other continuous variables were biotic and derived from the macroinvertebrate datasets. First, we conducted principal component analysis (PCA) separately on percentage abundances of macroinvertebrate taxa and on percentage abundances of the macroinvertebrate FFGs. The sample scores of the first principal components (PC1 macroinvertebrate taxa and PC1 macroinvertebrate FFGs) were then saved as new variables and used as two additional variables (9 and 10) in DistLM and dbRDA analyses.

3. Results

3.1. Environmental Characteristics of the Studied Sites

Water temperature of the sampled sites during the 2011 survey ranged between 19.1 and 32.7 °C (mean ± standard deviation = 25.6 ± 3.85 °C) and depended on the time of the day, pH varied between 7.0 and 10.0 (mean ± standard deviation = 8.4 ± 0.98), while conductivity between 36 and 16,760 µS cm−1 (mean ± standard deviation = 3165 ± 4436.9 µS cm−1), showing considerably higher values in the salt pans. Environmental characteristics of the studied sites with in situ measurements of their water properties are provided in Table 1.

3.2. Regional Ostracod Diversity

A total of 28,088 specimens of ostracods belonging to 16 species were collected during the two surveys from 20 sites, 11,416 specimens of six species from four sites in the 2009 survey, and 16,672 specimens of 13 species from 16 sites in the 2011 survey. Three grass pans (nos. 2, 10 and 11, see Table 1) sampled during the 2011 survey did not yield any ostracods. All identified species with their authorities and taxonomic assignments to families are listed in Table 2, while scanning electron micrographs (SEM) of the recorded species are shown in Figure 2, Figure 3 and Figure 4. Representatives of the family Cyprididae (13 species, 81% of the total species richness) and its subfamily Cypridopsinae (8 species, 50%) were the most species-rich taxa. In both surveys, Heterocypris giesbrechti (Figure 2A–H), Plesiocypridopsis newtoni (Figure 2I–M), and Potamocypris mastigophora (Figure 3A–C), were the most common species, each found at all four sites in the 2009 survey and at 9 sites (the two former species) or 7 (the latter one) out of 16 sites in the 2011 survey. On the other hand, as many as seven species were found only at single sites (Tables S1 and S2). Overall, during both surveys, species richness at the individual sampling sites ranged from 1 (one site) to 5 (five sites) with the mean ± standard deviation = 3.6 ± 1.3.

3.3. Ostracod Species and Assemblage Distribution across Pan Types

The distribution and groupings of ostracods across different pan types sampled during the 2011 survey are illustrated in Figure 5. Statistically significant differences were found in the ostracod assemblage structure and composition between the pan types (ANOSIM Global test R = 0.459, p = 0.006) with significant distinction of the open pan ostracod assemblages which differed from those of salt pans (ANOSIM pairwise test R = 0.667, p = 0.029) and from grass pans (ANOSIM pairwise test R = 0.467, p = 0.036), whereas assemblages of salt and grass pans did not differ significantly (ANOSIM pairwise test R = 0.200, p = 0.087). The ostracod assemblages of the three studied pan types differed by the dominance structure rather than by the species composition, i.e., the average abundance of the three key species (the most common and abundant in the studied area H. giesbrechti, P. newtoni and P. mastigophora) were different in the salt, grass, and open pans (Table 3, see also Figure 5). Based on the SIMPER analysis, the average assemblage similarity within the salt pans was 66% and was made up mainly of contribution (almost 90%) from clearly dominating H. giesbrechti (with high average percentage abundance of 74%). Assemblages of grass pans were most similar to those of salt pans but showed low average similarity (23%) and all three species H. giesbrechti (average contribution of 57%), P. newtoni (27%), and P. mastigophora (14%) had similar average percentage abundances (21–24%). At the open pan sites with average assemblage similarity of 30.5%, the total contribution was that of P. mastigophora (with high average abundance of 64%) (Table 3). However, one of the open pans (no. 6) was clearly distinct (Figure 5), hosting a very rare species, known so far only from this site, i.e., Potamocypris meissneri (Figure 3F) and a putative new species of the genus Limnocythere sp. (Figure 2P,Q). The ostracod assemblage found at the non-pan site (no. 16, a trough), with high abundance of P. mastigophora, was most similar (Bray-Curtis similarity of ca. 56%) to the assemblages from the open pans nos. 5 and 15 as well as from the grass pan no. 4 (Figure 5).
Finally, there was no significant correlation between site geographic distance and site assemblage similarity (RELATE statistics Rho = –0.078, p = 0.713).

3.4. Macroinvertebrate Communities and Functional Feeding Groups

The macroinvertebrate samples contained in total 1987 individuals belonging to 24 taxa, of which the majority (95%) belonged to six orders of insects (Coleoptera, Diptera, Ephemeroptera, Heteroptera, Lepidoptera, Odonata) (Table S1). True bugs of the suborder Heteroptera were the most abundant (34% of the total number of collected individuals), followed by Diptera (31%) with the most abundant and commonly occurring family Chironomidae (27%), and by Coleoptera (22%) with the second most abundant family Dytiscidae (19%) (Table S1). The first PCA axis (Table S3) of the macroinvertebrate taxa abundances explained 34.8% of the total variance, and was associated positively mainly with water boatmen hemipteran family Corixidae (0.877), and negatively with dipteran family Chironomidae (–0.424).
As regards functional feeding groups (FFGs), predators represented 63% of the macroinvertebrate taxa. This FFG included two families of Odonata and Coleoptera, three families of Diptera, and eight families of Heteroptera (Table S1). Oligochaeta, Ephemeroptera, and four families of Diptera identified as collectors were the second dominant FFG (25%) observed at the studied sites. The percentage abundance of each of the remaining three FFGs (filterers, shredders, and scrapers) was 4% (Table S1). PCA analysis using percentage abundances of FFGs as variables showed the highest positive correlation of collectors-gatherers (0.690) and negative correlation of predators (–0.719) with the first component PC1, which explained 85.3% of the total variance (Table S4).
Additionally, in the studied pans we found microcrustacean copepods of the families Cyclopidae and Diaptomidae as well as cladocerans of the families Macrothricidae and Moinidae (Table S1).

3.5. Effect of Environmental Variables on Ostracod Diversity and Assemblage Composition

Pan type, water conductivity, and FFGs PC1 were selected as significant environmental correlates of ostracod assemblage structure and composition (DistLM Marginal tests, p < 0.05, Table 4). These three variables each alone explained >20% of variation in the ostracod response dataset. The best two models based on the AICc criterion (with the lowest AICc value of 106.1–106.5 and correlation of 0.217–0.242) had one variable each: Conductivity or FFGs PC1. However, two-variable model (with conductivity and FFGs PC1), achieved nearly the same AICc value (106.9) as the two best models but had clearly higher correlation (0.382) (Table 4: Best models).
The best parsimonious two-variable DistLM model as a dbRDA ordination plot where the first axis accounted for 82.7% of the fitted model variation and 31.6% of the total variation is visualized in Figure 6. The first dbRDA axis is positively correlated with water electrical conductivity (0.656) and negatively correlated with FFGs PC1 (–0.755). It clearly separates the salt pans (located on the right side of the plot) with high water conductivity (mean ± standard deviation = 8807 ± 6118.1 µS cm−1) and the highest ratio of predaceous (mean ± standard deviation = 87.3 ± 15.52%) but the lowest ratio of collector-gatherer (5.4 ± 6.05%) macroinvertebrates from the remaining sites. This axis provides also some separation between the grass pans (mean electrical conductivity = 1538 ± 1238.8 µS cm−1 and mean percentage of predators = 67.5 ± 23.41%) and the open pans (mean electrical conductivity = 775 ± 640.0 µS cm−1 and mean percentage of predators = 53.0 ± 13.04%) as well as from the non-pan site. The second axis does not provide any division of the three types of pans. Although the first two dimensions captured 100% of the fitted model variation, there is still residual variation in the original data matrix since the two first axes together explain 38.2% of the total variation (Figure 6).
Of the three species selected by the SIMPER analysis as responsible for the pan type segregation, Heterocypris giesbrechti and Plesiocypridopsis newtoni are located on the right side of the plot (Figure 6) and are positively correlated with the dbRDA1 (correlation coefficients 0.767 and 0.160, respectively). These species with high relative abundances are most characteristic for the salt (especially H. giesbrechti) and grass pans. On the other hand, Potamocypris mastigophora, which negatively correlated with the dbRDA1 (–0.256), is situated on the left side of the plot and occurred typically in high percentage abundances in the open pans.

4. Discussion

4.1. Ostracods of the North West Province

Whereas the non-marine ostracod fauna of South Africa (with the total reported species richness of ca. 120–125) has been relatively well-explored in the Western (ca. 60 species) and Eastern (43 species) Cape provinces as well as from KwaZulu Natal (ca. 50 species) [19,21,67], little appears to be known about the distribution of species and the structure of ostracod assemblages of the North West province (Table 2).
In the current study, 16 ostracod species were found, of which 13 have not been previously recorded from the North West (Table 2). One species has meanwhile been described as new from these collections, i.e., Potamocypris meissneri (in [66]) and three further species new to science (Pseudocypris sp., Hemicypris sp. and Limnocythere sp. ex gr. stationis) are currently being described. The present collections bring the total number of extant non-marine ostracod species recorded in the North West to 26 (Table 2) and show that further investigations may yield an even greater taxonomic diversity of ostracods in this region.
Species composition of the ostracod inventory of the North West known so far shows, as expected, that the general pattern of suprageneric taxonomic diversity with the most species-rich family Cyprididae (19 species, 73% of the total species richness of 26 species) and subfamily Cypridopsinae (9 species, 35%) is similar to that of the non-marine surface ostracod species inventories of the KwaZulu Natal (75% of species in Cyprididae and 21% in Cypridopsinae: [67]), of the Eastern Cape (77% species in Cyprididae and 26% in Cypridopsinae: [21]), as well as of Botswana (76% species in Cyprididae and 24% in Cypridopsinae: [68]). The most common and abundant ostracod species collected during the present study are widespread taxa which are not rare or threatened. Heterocypris giesbrechti has been found previously in North, West, East, and Central Africa [69,70,71] and occurs also in South Africa: in the KwaZulu Natal [67] and Eastern Cape [21]. Potamocypris mastigophora is also widely distributed across Sub-Saharan Africa (including South Africa) [19,69] with some records in southern Palaearctic [18,72], while Plesiocypridopsis newtoni occurs throughout Africa and beyond [18,73], and could constitute a Palaearctic introduction in South Africa. Other species were more limited in their distribution patterns in the studied area.
Nevertheless, the absence in our collection of a number of genera often recorded from various temporary wetlands in southern Africa, e.g., Cypretta Vávra, 1895; Cypricercus Sars, 1895; Eundacypris Martens, 1986; Gomphocythere Sars, 1924; Globocypris Klie, 1939; Megalocypris Sars, 1898; Ovambocythere Martens, 1989; Physocypria Vávra, 1897; Ramotha Martens, 1992 or Zonocypris Müller, 1898 (see [19,74]) shows that the fauna of temporary waters of this area can be regionally diversified, reflecting environmental specificity [75]. Significant differences in ostracod generic diversity (Limnocythere as one genus in common) between our study (9 genera in total) and that by [76] in pans of the Mpumalanga province of South Africa (6 genera) seem to support this hypothesis. The same appears true when comparing our results with those reported by [54] from three seasonal open mud pans and two grass pans in the Gauteng province and one open mud pan in the North West (the Eliazar pan already mentioned above). Of the total of 8 species found by these authors [54], only one (Sarscypridopsis aculeata) was also recorded in our study. Finally, of the six species reported from three temporary pans in central and northern Botswana [77], only one (Potamocypris mastigophora) was recorded in our study.

4.2. Ostracods-Environment Relationships

The results obtained in our study of the endorheic wetlands in the small area of the North West indicated that the three pan types supported diverse ostracod assemblages, differing mostly in the dominance structure and less in the species composition.
Considering that the three most common and abundant species recorded in the studied sites have relatively wide ecological tolerances [21,33,67,71,73,78,79,80,81,82,83], including conductivity, clearly other important, and possibly mutually correlated, drivers of non-random ostracod distribution and domination appeared to play a role. Indeed, even at the small local and habitat scale, different ostracod species may dominate in different environments, according not only to their tolerances to hydrochemistry (conductivity, pH, ionic ratios) or oxygen requirements, but also to their size, mode of life or vulnerability to predators, among others [84].
The relative abundance of predaceous and collector-gatherer macroinvertebrate functional feeding groups (expressed as the scores of PC1) was also selected as a significant environmental correlate of the ostracod assemblage structure and composition. Ostracod assemblages from the salt pans co-occurred with the highest ratio of predators. The grass pan assemblages appeared together with less abundant predators accompanied by collectors, whereas ostracods from the open pans were typically found with the lowest predator ratio, but the highest ratio of gathering collectors. In waterbodies without fish, several aquatic invertebrate taxa could prey on ostracods, including hemipterans or larval dytiscid beetles [84,85,86]. The ostracod assemblage structure may be impacted directly depending on predators specific selectivity and vulnerability of the prey. Several macroinvertebrate predators are size selective having clear preferences for smaller or larger ostracods [85,87]. Size-selective predation, which can be related to the predator specific trade-off between ease of detection and ease of capture of the prey, could not only affect the size distribution of specimens of individual species, but may also affect the dominance structure of an ostracod assemblage consisting of species differing in size. In the salt pans with the highest ratio of predators, consisting mostly of corixid and notonectid hemipterans, the dominant ostracod species was H. giesbrechti, which is the largest (ca. 0.79–0.90 mm in length, see [88]) of the three key species responsible of the ostracod assemblage separation among the studied pans (P. newtoni ca. 0.67–0.75 mm [73], while P. mastigophora ca. 0.52 [89]). On the other hand, in the open pans with the lowest ratio of predators, small P. mastigophora typically dominated. Predation pressure and size selectivity may certainly be reduced or modified by ostracod antipredator adaptations [85,90,91] as well as potential shifts in some life-history traits (as in cladocerans, see e.g., [92]). Our results did not allow to distinguish between such potential effects, but if (apart for size), several biological traits of the three most common species in the studied pans remain very similar (e.g., similar nektobenthic mode of life or no clear cryptic coloration), predator size-selectivity needs to be considered as a potential driver, structuring ostracod assemblages in pans of the study area, especially on relatively small spatial scales with low water depth and absence of vegetation where potential for vertical migration and hiding in plants is very limited.
In our study percentage abundance of predators was negatively correlated with that of gathering collectors, so that in the open pans both groups were co-dominant. By using the same resources and/or disturbing the habitat, making resources more difficult to access, some gathering collectors may potentially be competitive with ostracods. Modig et al. [93] showed experimentally that by the mechanical disturbance of sediment which may have caused a burial of phytodetritus, amphipods had negative effects on the feeding rate by ostracods on diatoms.
On the other hand, if the taxon richness and proportion of predatory macroinvertebrates in temporary habitats are positively correlated with the hydroperiod length (e.g., [11,94,95]), the relationship between the ratio of predators/collector-gatherers and ostracod assemblage structure revealed in our study may be also indirectly related to the hydroperiod. The significance of habitat permanence in structuring freshwater invertebrate communities has long been known [11], and has also been shown to be one of the important variables (based on invertebrate communities) in the segregation of reproductive modes (geographical parthenogenesis) in the Holarctic ostracod species Eucypris virens [96]. Whether the studied salt pans in the North West, harboring the highest proportion of predators and co-occurring ostracod assemblages dominated by Heterocypris giesbrechti are more stable, longer-standing waterbodies than those of the grass or open pans with other ostracod assemblages remains to be further studied. Our results suggest, however, that the biotic factors (principal components summarizing invertebrate functional feeding groups) may be more important in shaping ostracod assemblage structures than previously thought.

5. Conclusions

The current study extends the knowledge of the distribution of ostracods in South Africa, and describes for the first time the diversity in the structure of ostracod assemblages in different pan type habitats of the North West province, where biodiversity estimations have rarely included ostracods, skewing biodiversity assessments in favor of macroinvertebrates. By revealing that the pan type, water electrical conductivity, and abundance of macroinvertebrate predators and collector-gatherers best explained the variation in the ostracod dataset from the studied area, the present study provides a basis for continuing research on how ostracod assemblages vary in relation to both biotic (accompanying macroinvertebrates) and abiotic (water chemistry) environmental variables in endorheic wetlands and other similar habitats of other under-studied semi-arid areas of southern Africa. Identifying and understanding the drivers of the compositional structure of ostracod assemblages of temporary pans provide a baseline for further studies on the assessment of the impact of both climate change and direct anthropogenic disturbances on these endangered unpredictable ecosystems and facilitates application of ostracods in paleoenvironmental reconstructions. As evidenced by our collection of undescribed species and new records for the province, several species remain to be sampled (including new to science) from this part of southern Africa. Our scanning electron microscopy atlas may provide some help in identifying ostracods for further studies.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/d15050614/s1. Table S1: Overview of ostracod species and other invertebrate taxa collected in 2011 from 16 study sites in North West province of South Africa. Abundances of individual taxa at the sites are presented as percentages. Names of macroinvertebrate taxa are accompanied by abbreviations of the functional feeding groups (FFGs) they represent: Cg—collector-gatherers, Ft—filterers, Pr—predators, Sc—scrapers/grazers, Sh—shredders. Table S2: Abundances of ostracod taxa collected in 2009 from 4 study sites in North West province of South Africa. Table S3: Results of the principal component analysis on relative abundances of the macroinvertebrate taxa accompanying ostracods collected in 2011 from 16 study sites in North West province of South Africa. Data on eigenvalues, explained portion of the total variation, and on coefficients of variables making up the first three PC’s are shown. Macroinvertebrate taxa which correlated the most with the PC1 are highlighted in bold. Table S4: Results of principal component analysis on relative abundances of the macroinvertebrate functional feeding groups (FFGs) accompanying ostracods collected in 2011 from 16 study sites in North West province of South Africa. Data on eigenvalues, explained portion of the total variation and on coefficients of variables making up the first three PC’s are shown. Macroinvertebrate FFGs which correlated the most with the PC1 are highlighted in bold.

Author Contributions

Conceptualization, A.S. and T.N.; methodology, A.S. and T.N.; formal analysis, A.S. and T.N.; investigation, A.S., K.M. and T.N.; resources, W.M. and T.N.; data curation, A.S., K.M. and T.N.; writing—original draft preparation, A.S., K.M., W.M. and T.N.; writing—review and editing, A.S. and T.N.; visualization, A.S.; supervision, T.N.; project administration, T.N. and K.M.; funding acquisition, T.N. and A.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by (1) the POLISH NATIONAL AGENCY FOR ACADEMIC EXCHANGE NAWA as part of the Bekker NAWA Programme, grant number BPN/BEK/2021/1/00421/U/00001, (2) the SYNTHESYS+ project, H2020 Research Infrastructures Programme, contract number SEP-210489579, and (3) the UNIVERSITY OF GDANSK, grant numbers L-155-4-0089-1 and 531-D200-D895-23.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding authors.

Acknowledgments

This is a collaborative study of the University of Gdansk, Poland and the Royal Belgian Institute of Natural Sciences (RBINS, Brussels, Belgium) within the framework financed by the Polish National Agency for Academic Exchange NAWA as part of the Bekker NAWA Programme (BPN/BEK/2021/1/00421/U/00001: Drivers controlling biodiversity of non-marine ostracods (Crustacea: Ostracoda) from southern Africa across environmental and spatial gradients) through which T.N. was hosted at the RBINS for an extended stay. We are grateful to Sampie van der Merwe, manager of the Barberspan Bird Sanctuary, as well as to Amos Koloti, Andrew Mvundle and Steven Segang, research assistants from the reserve, for providing accommodation, field laboratory facilities and their help and logistic support in the field. The landowners are thanked for giving permission to access and work on their lands. We also thank Malwina Laskowska and Lucyna Namiotko (University of Gdansk) for their assistance in sample processing and preliminary identification of invertebrates. Julien Cillis and Laetitia Despontin (RBINS, Brussels, Belgium) offered technical assistance with the SEM and Isa Schön facilitated the stay of T.N. at RBINS (Brussels, Belgium).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Map of the study area showing locations of the 16 sampling sites in the central part of the North West province of South Africa.
Figure 1. Map of the study area showing locations of the 16 sampling sites in the central part of the North West province of South Africa.
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Figure 2. SEM iconography of ostracods found at the studied sites in North West province of South Africa: Heterocypris giesbrechti (A–H); Plesiocypridopsis newtoni (I–M); Hemicypris sp. (N,O); Limnocythere sp. ex gr. stationis (P,Q); Limnocythere cf. inopinata (R,S). H. giesbrechti: (A) male, RV, external view. (B) male, LV, external view. (C) male, Cp, dorsal view. (D) female, Cp, right lateral view. (E) female, LV, external view. (F) female, Cp, dorsal view. (G) female, LV, internal view. (H) female, RV, internal view. P. newtoni: (I) female, Cp, dorsal view. (J) female, RV, external view. (K) female, LV, external view. (L) female, LV, internal view. (M) female, RV, internal view. Hemicypris sp.: (N) female, Cp, left lateral view. (O) female, Cp, dorsal view. Limnocythere sp. ex gr. stationis: (P) female, RV, external view. (Q) female, Cp, dorsal view. L. cf. inopinata: (R) female, Cp, right lateral view. (S) female, Cp, left lateral view. Scale = 500 μm for (N,O); 300 μm for (P,Q); 200 μm for (A–M); 100 μm for (R,S).
Figure 2. SEM iconography of ostracods found at the studied sites in North West province of South Africa: Heterocypris giesbrechti (A–H); Plesiocypridopsis newtoni (I–M); Hemicypris sp. (N,O); Limnocythere sp. ex gr. stationis (P,Q); Limnocythere cf. inopinata (R,S). H. giesbrechti: (A) male, RV, external view. (B) male, LV, external view. (C) male, Cp, dorsal view. (D) female, Cp, right lateral view. (E) female, LV, external view. (F) female, Cp, dorsal view. (G) female, LV, internal view. (H) female, RV, internal view. P. newtoni: (I) female, Cp, dorsal view. (J) female, RV, external view. (K) female, LV, external view. (L) female, LV, internal view. (M) female, RV, internal view. Hemicypris sp.: (N) female, Cp, left lateral view. (O) female, Cp, dorsal view. Limnocythere sp. ex gr. stationis: (P) female, RV, external view. (Q) female, Cp, dorsal view. L. cf. inopinata: (R) female, Cp, right lateral view. (S) female, Cp, left lateral view. Scale = 500 μm for (N,O); 300 μm for (P,Q); 200 μm for (A–M); 100 μm for (R,S).
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Figure 3. SEM iconography of ostracods found at the studied sites in North West province of South Africa: Potamocypris mastigophora (A–C); Potamocypris cf. deflexa (D,E); Potamocypris meissneri (F); Potamocypris cf. gibbula (G,H); Sarscypridopsis aculeata (I–L); Sarscypridopsis cf. katesae (M–O); Sarscypridopsis elizabethae (P–R). P. mastigophora: (A) female, LV, internal view. (B) female, RV, internal view. (C) female RV, external view. P. cf. deflexa: (D) female, Cp, left lateral view. (E) female, Cp, dorsal view. P. meissneri: (F) female, Cp, right lateral view. P. cf. gibbula: (G) female, Cp, left lateral view. (H) female, Cp, dorsal view. S. aculeata: (I) female, Cp, dorsal view. (J) female, Cp, right lateral view. (K) female, Cp, left lateral view. (L) female, Cp, ventral view. S. cf. katesae: (M) female, Cp, left lateral view. (N) female, Cp, dorsal view. (O) female, detail of surface. S. elizabethae: (P) female, Cp, left lateral view. (Q) female, Cp, dorsal view. (R) female, detail of surface. Scale = 500 μm for (I–N,P,Q); 300 μm for (D,E,G,H); 100 μm for (A,B,F); 50 μm for (R); 20 μm for (C,O).
Figure 3. SEM iconography of ostracods found at the studied sites in North West province of South Africa: Potamocypris mastigophora (A–C); Potamocypris cf. deflexa (D,E); Potamocypris meissneri (F); Potamocypris cf. gibbula (G,H); Sarscypridopsis aculeata (I–L); Sarscypridopsis cf. katesae (M–O); Sarscypridopsis elizabethae (P–R). P. mastigophora: (A) female, LV, internal view. (B) female, RV, internal view. (C) female RV, external view. P. cf. deflexa: (D) female, Cp, left lateral view. (E) female, Cp, dorsal view. P. meissneri: (F) female, Cp, right lateral view. P. cf. gibbula: (G) female, Cp, left lateral view. (H) female, Cp, dorsal view. S. aculeata: (I) female, Cp, dorsal view. (J) female, Cp, right lateral view. (K) female, Cp, left lateral view. (L) female, Cp, ventral view. S. cf. katesae: (M) female, Cp, left lateral view. (N) female, Cp, dorsal view. (O) female, detail of surface. S. elizabethae: (P) female, Cp, left lateral view. (Q) female, Cp, dorsal view. (R) female, detail of surface. Scale = 500 μm for (I–N,P,Q); 300 μm for (D,E,G,H); 100 μm for (A,B,F); 50 μm for (R); 20 μm for (C,O).
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Figure 4. SEM iconography of ostracods found at the studied sites in North West province of South Africa: Pseudocypris sp. (A); Sclerocypris methueni (B–D); Sclerocypris exserta (E,F). Pseudocypris sp.: (A) female RV, external view. S. methueni: (B) female, Cp, dorsal view. (C) female, LV, external view. (D) female, RV, external view. S. exserta: (E) female, LV, external view. (F) female, RV, external view. Scale = 2000 μm for (B–D); 1000 μm for (E,F); 200 μm for (A).
Figure 4. SEM iconography of ostracods found at the studied sites in North West province of South Africa: Pseudocypris sp. (A); Sclerocypris methueni (B–D); Sclerocypris exserta (E,F). Pseudocypris sp.: (A) female RV, external view. S. methueni: (B) female, Cp, dorsal view. (C) female, LV, external view. (D) female, RV, external view. S. exserta: (E) female, LV, external view. (F) female, RV, external view. Scale = 2000 μm for (B–D); 1000 μm for (E,F); 200 μm for (A).
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Figure 5. Shade plot illustrating the distribution and groupings of ostracods across different pan types in the North West province based on species percentage abundance shown in proportional shading intensity scale. Samples and species are independently placed in the nearest neighbor order, based for samples on Bray-Curtis similarities on percentages, and for species on the association index on species-standardized data. The sample axis is constrained by the pan type.
Figure 5. Shade plot illustrating the distribution and groupings of ostracods across different pan types in the North West province based on species percentage abundance shown in proportional shading intensity scale. Samples and species are independently placed in the nearest neighbor order, based for samples on Bray-Curtis similarities on percentages, and for species on the association index on species-standardized data. The sample axis is constrained by the pan type.
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Figure 6. Ordination plot of the two first axes of distance-based redundancy analysis (dbRDA) depicting the best two-variable DistLM fitted model of significant relationships between ostracod dataset and environmental variables.
Figure 6. Ordination plot of the two first axes of distance-based redundancy analysis (dbRDA) depicting the best two-variable DistLM fitted model of significant relationships between ostracod dataset and environmental variables.
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Table
Table 1. Data on geographical location, water properties, and other environmental characteristics of the sites from where ostracods and other invertebrates were collected for the present study in the North West province of South Africa.
Table 1. Data on geographical location, water properties, and other environmental characteristics of the sites from where ostracods and other invertebrates were collected for the present study in the North West province of South Africa.
SiteLongitude ELatitude SAltitude
(m A.S.L.)		Water Temperature (°C)pHElectrical Conductivity
(µS/cm)		Pan TypeLand UseFish Presence
(Yes/No)		Macrophyte Coverage
(%)		Substrate TypeSurface Area (km2)
126°20′39.00″25°35′42.00″134727.510.010,670salturban/degradedN10muddy0.97
226°20′43.00″25°36′49.00″135426.78.52670grassurban/degradedN40sandy-muddy<0.01
326°23′59.00″ 25°36′46.00″135322.49.516,760saltnaturalN0muddy0.73
426°24′26.47″25°36′10.02″135729.38.5358grassnaturalN90sandy0.08
526°25′16.00″25°31′32.00″137125.110.01123openurban/degradedN25muddy0.26
626°26′42.00″25°32′20.00″137225.87.036openurban/degradedN0sandy-muddy0.05
726°26′29.00″25°37′13.00″134521.48.52700grassnaturalN40sandy0.56
826°30′11.25″25°36′34.61″135432.78.53900saltnaturalY70sandy0.11
926°30′59.10″25°36′32.92″135432.78.53900saltnaturalY70sandy4.05
1026°32′54.00″25°35′51.00″134422.88.01109grassnaturalY95sandy-muddy0.04
1126°33′08.00″ 25°36′02.00″135825.97.51112grassnaturalY95sandy-muddy0.04
1226°33′19.00″25°36′32.00″135727.78.53010grassnaturalN80sandy0.01
1326°35′28.70″25°36′11.08″134722.38.51101grassnaturalY45sandy17.3
1426°36′38.00″25°34′54.00″134722.57.0519grassnaturalY90sandy-muddy1.47
1526°34′23.00″25°33′11.00″137119.17.01165opennaturalN75sandy0.04
1626°26′30.00″25°37′44.00″136025.49.5512othernaturalN0concrete/artificial<0.001
Table
Table 2. Preliminary checklist of living non-marine Ostracoda reported from North West province of South Africa. Included are only those published records which were identified down to species level or left in open nomenclature but containing specific epithet within a given genus. The records are listed in a taxonomically based order and in presently accepted taxonomic conventions following [18], although names as originally published are also provided following the source reference abbreviations. Sources: (1) [54] (Eliazar pan 25 km W Potchefstroom), (2) [55] (Eliazar pan 25 km W Potchefstroom), (3) [56] (Barberspan, a total of 8 species recorded but 7 left in open nomenclature not included here), (4) [57] (dolomitic springs in C-E North West), (5) [58] (dolomitic springs in C-E North West), (6) [59] (Molopo Oog), (7) [60] (Molopo Oog), (8) [19] (9) [61] (10) [62] (Molopo Oog), (11) [63] (Molopo Oog), (12) [64] (Molopo Oog), (13) [65] (Molopo Oog), (14) [66] (Ganalaagte pan, site no. 6 in the present paper), (15) present paper 2009 survey, (16) present paper 2011 survey.
Table 2. Preliminary checklist of living non-marine Ostracoda reported from North West province of South Africa. Included are only those published records which were identified down to species level or left in open nomenclature but containing specific epithet within a given genus. The records are listed in a taxonomically based order and in presently accepted taxonomic conventions following [18], although names as originally published are also provided following the source reference abbreviations. Sources: (1) [54] (Eliazar pan 25 km W Potchefstroom), (2) [55] (Eliazar pan 25 km W Potchefstroom), (3) [56] (Barberspan, a total of 8 species recorded but 7 left in open nomenclature not included here), (4) [57] (dolomitic springs in C-E North West), (5) [58] (dolomitic springs in C-E North West), (6) [59] (Molopo Oog), (7) [60] (Molopo Oog), (8) [19] (9) [61] (10) [62] (Molopo Oog), (11) [63] (Molopo Oog), (12) [64] (Molopo Oog), (13) [65] (Molopo Oog), (14) [66] (Ganalaagte pan, site no. 6 in the present paper), (15) present paper 2009 survey, (16) present paper 2011 survey.
SpeciesReferences
Family Cyprididae Baird, 1845
Subfmily Cypridinae Baird, 1845
Pseudocypris expansa Sars, 19241, 3
Pseudocypris sp.16
Subfmily Cypridopsinae Kaufmann, 1900
Plesiocypridopsis inaequivalva (Klie, 1933)1 and 2 (as Cypridopsis inaequivalva Klie)
Plesiocypridopsis newtoni (Brady & Robertson, 1870)15, 16
Potamocypris cf. deflexa (Sars, 1924)16
Potamocypris cf. gibbula (Sars, 1924)15
Potamocypris mastigophora (Methuen, 1910)15, 16
Potamocypris meissneri Szwarc et al. 202114, 16
Sarscypridopsis aculeata (Costa, 1847)15
Sarscypridopsis elizabethae (Sars, 1924)15
Sarscypridopsis cf. katesae (Hartmann, 1957)16
Subfamily Cyprinotinae Bronstein, 1947
Hemicypris congenera (Vávra, 1897)1 (as Cyprinotus congener Vávra, doubtful identification, may refer to Heterocypris congenera (Vávra, 1897)),
Hemicypris sp.14 (as Hemicypris cf. inversa (Daday, 1913)), 16
Heterocypris giesbrechti (G.W. Müller, 1898)15, 16
Subfamily Herpetocypridinae Kaufmann, 1900
Chrissia levetzovi Hartmann, 19579
Humphcypris greenwoodi Martens, 19975, 8
Subfamily Megalocypridinae Rome, 1965
Sclerocypris exserta Sars, 192416
Sclerocypris methueni (Kempf, 2015)16
Sclerocypris tuberculata (Sars, 1924)1 (as Megalocypris tuberculata Sars)
Family Ilyocyprididae Kaufmann, 1900
Ilyocypris cf. gibba (Ramdohr, 1808)16
Family Limnocytheridae Sars, 1925
Limnocythere sp. ex gr. stationis14 (as Limnocythere cf. stationis Vávra, 1897), 16
Limnocythere cf. inopinata (Baird, 1843)16
Gomphocythere capensis G.W. Müller, 19144, 5, 10
Family Darwinulidae Brady & Robertson, 1885
Alicenula inversa (Martens & Rossetti, 1997) 6 (as Darwinula inversa), 7, 8
Darwinula stevensoni (Brady & Robertson, 1870)8
Vestalenula molopoensis (Martens & Rossetti, 1997)6 (as Darwinula molopoensis), 7, 8, 11, 12, 13
Table
Table 3. Results of the SIMPER analysis listing ostracod species that contributed most to the average Bray-Curtis similarity (AvSim) among sites within each pan type and to the average dissimilarity (AvDiss) between all pair of sites among three pan types. For each species, the average percentage abundance (AvA) and individual percentage contribution (CSim/CDiss) to the average similarity/dissimilarity within/between the pan types are given.
Table 3. Results of the SIMPER analysis listing ostracod species that contributed most to the average Bray-Curtis similarity (AvSim) among sites within each pan type and to the average dissimilarity (AvDiss) between all pair of sites among three pan types. For each species, the average percentage abundance (AvA) and individual percentage contribution (CSim/CDiss) to the average similarity/dissimilarity within/between the pan types are given.
Salt PansGrass PansOpen PansSalt vs.
Grass Pans		Salt vs.
Open Pans		Grass vs.
Open Pans
AvSim = 66.36AvSim = 23.34AvSim = 30.54AvDiss = 66.16AvDiss = 99.66AvDiss = 85.43
SpeciesAvACSimAvACSimAvACSimCDissCDissCDiss
Heterocypris giesbrechti74.0989.6524.0456.770.000.0037.9937.1714.07
Plesiocypridopsis newtoni21.7310.3322.4027.310.240.0018.8510.7813.03
Potamocypris mastigophora0.040.0021.4213.8363.88100.0016.1832.0433.20
Table
Table 4. Results of the distance-based linear model DistLM (marginal tests and five best parsimonious models) for the ostracod data from the North West endorheic wetlands using the best selection procedure and the modified Akaike Information Criterion (AICc) as selection criterion of environmental variables. R2 = proportion of the variation in the ostracod dataset explained by environmental data, RSS residual sum of squares, FFGs PC1 = loadings of the first component of PCA on macroinvertebrate functional feeding groups.
Table 4. Results of the distance-based linear model DistLM (marginal tests and five best parsimonious models) for the ostracod data from the North West endorheic wetlands using the best selection procedure and the modified Akaike Information Criterion (AICc) as selection criterion of environmental variables. R2 = proportion of the variation in the ostracod dataset explained by environmental data, RSS residual sum of squares, FFGs PC1 = loadings of the first component of PCA on macroinvertebrate functional feeding groups.
Marginal Tests VariableSum of Squares (Trace)Pseudo-FPR2
Pan type19,1132.7030.0130.4740
Conductivity97623.5140.0140.2421
FFGs PC187473.0470.0300.2169
Macroinvertebrate PC167162.1980.0510.1666
Surface area86961.3750.2090.2157
Substrate11,6791.2230.2570.2896
Fish presence73121.1080.3450.1813
pH31950.9460.4070.0792
Human impact22660.6550.6220.0562
Vegetation cover36940.5040.8810.0916
Best Models Variable SelectionNo variablesAICcRSSR2
Conductivity1106.1130,5620.2421
FFGs PC11106.5431,5780.2169
Conductivity and FFGs PC12106.9324,9260.3819
Macroinvertebrate PC11107.3533,6080.1666
pH and FFGs PC12108.2127,5020.3180
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Szwarc, A.; Martens, K.; Meissner, W.; Namiotko, T. Evidence for Conductivity- and Macroinvertebrate-Driven Segregation of Ostracod Assemblages in Endorheic Depression Wetlands in North West Province of South Africa. Diversity 2023, 15, 614. https://doi.org/10.3390/d15050614

AMA Style

Szwarc A, Martens K, Meissner W, Namiotko T. Evidence for Conductivity- and Macroinvertebrate-Driven Segregation of Ostracod Assemblages in Endorheic Depression Wetlands in North West Province of South Africa. Diversity. 2023; 15(5):614. https://doi.org/10.3390/d15050614

Chicago/Turabian Style

Szwarc, Agata, Koen Martens, Włodzimierz Meissner, and Tadeusz Namiotko. 2023. "Evidence for Conductivity- and Macroinvertebrate-Driven Segregation of Ostracod Assemblages in Endorheic Depression Wetlands in North West Province of South Africa" Diversity 15, no. 5: 614. https://doi.org/10.3390/d15050614

APA Style

Szwarc, A., Martens, K., Meissner, W., & Namiotko, T. (2023). Evidence for Conductivity- and Macroinvertebrate-Driven Segregation of Ostracod Assemblages in Endorheic Depression Wetlands in North West Province of South Africa. Diversity, 15(5), 614. https://doi.org/10.3390/d15050614

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