Diversity2015, 7(1), 3-15; doi:10.3390/d7010003 - published 9 January 2015 Show/Hide Abstract
Abstract: Desert springs, which harbor diverse and endemic invertebrate assemblages, are often used as refuge habitats for protected fish species. Additionally, many of these springs have been colonized by invasive fish species. However, the potential impacts of recently established fish populations on invertebrate communities in desert springs have been relatively unexplored. We conducted a mesocosm experiment to assess the impact of both protected and invasive fish on community structure of spring-dwelling invertebrates focusing on zooplankton. Experimental populations of spring zooplankton communities were established and randomly assigned to one of three treatments, (1) invasive western mosquitofish (Gambusia affinis); (2) endangered Mohave tui chub (Siphateles bicolor mohavensis); and (3) fishless control. Final populations of zooplankton and fish were sampled, sorted, identified and counted. The treatment differences of zooplankton communities were analyzed by comparing the densities of six major zooplankton taxa. Further, we performed nonmetric multidimensional scaling (NMDS) to visualize the patterns of zooplankton community assemblages. Four zooplankton taxa, crustacean nauplii, cladocera, calanoid and cyclopoid copepods had significantly lower densities in fish treatments compared to fishless control. Overall, invasive mosquitofish caused a 78.8% reduction in zooplankton density, while Mohave tui chub caused a 65.1% reduction. Both protected and invasive fish had similar effects on zooplankton except for cladocerans where tui chub caused a 60% reduction in density, whereas mosquitofish virtually eliminated cladocerans. The presence of fish also had a significant effect on zooplankton community structure due to population declines and local extirpations presumably due to fish predation. This work shows that conservation-translocations undertaken to conserve protected fish species may impact spring-dwelling invertebrate communities, and such impacts are similar to impacts due to colonization by invasive fish species.
Diversity2014, 6(4), 844-854; doi:10.3390/d6040844 - published 18 December 2014 Show/Hide Abstract
Abstract: There have been few assessments of the performance of alternative resistance surfaces, and little is known about how connectivity modeling approaches differ in their ability to predict organism movements. In this paper, we evaluate the performance of four connectivity modeling approaches applied to two resistance surfaces in predicting the locations of highway crossings by American black bears in the northern Rocky Mountains, USA. We found that a resistance surface derived directly from movement data greatly outperformed a resistance surface produced from analysis of genetic differentiation, despite their heuristic similarities. Our analysis also suggested differences in the performance of different connectivity modeling approaches. Factorial least cost paths appeared to slightly outperform other methods on the movement-derived resistance surface, but had very poor performance on the resistance surface obtained from multi-model landscape genetic analysis. Cumulative resistant kernels appeared to offer the best combination of high predictive performance and sensitivity to differences in resistance surface parameterization. Our analysis highlights that even when two resistance surfaces include the same variables and have a high spatial correlation of resistance values, they may perform very differently in predicting animal movement and population connectivity.
Diversity2014, 6(4), 827-843; doi:10.3390/d6040827 - published 11 December 2014 Show/Hide Abstract
Abstract: Tropical mangroves are considered one of the most productive ecosystems of the world, being characterized as nurseries and food sources for fish and other animals. Microorganisms play important roles in these environments, and the study of bacterial communities is of paramount importance for a better comprehension of mangrove dynamics. This study focused on the structure and composition of bacterial communities in mangrove sediments at different depths and points, located in Southeastern Brazil. Terminal Restriction Fragment Length Polymorphism (T-RFLP) was used to determine the community structure, and 16S rRNA gene pyrosequencing was used to characterize the community composition. Redundancy analysis of T-RFLP patterns revealed differences in bacterial community structure according to soil attributes and depth. The parameters K and depth presented significant correlation with general community structure. Most sequences were classified into the phylum Proteobacteria (88%), which presented differences according to the depth, where the classes Betaproteobacteria (21%) and Deltaproteobacteria (16%) were abundant at 10 cm and Epsilonproteobacteria (35%) was abundant at 40 cm depth. Clear differences were observed in community composition as shown by the differential distribution of the phyla Firmicutes (1.13% and 3.8%, for 10 cm and 40 cm respectively), Chloroflexi (2.8% and 0.75%), and Acidobacteria (2.75% and 0.57%) according to the depth. Bacterial diversity measurements indicated higher diversity in shallow samples. Taken together, our findings indicate that mangrove holds a diverse bacterial community, which is shaped by the variations found in the ecosystem, such as sediment properties and depth.
Diversity2014, 6(4), 792-826; doi:10.3390/d6040792 - published 9 December 2014 Show/Hide Abstract
Abstract: Manioc is an important root crop in the tropics and the most important staple food in the Amazon. Manioc is diverse but its diversity has not yet been clearly associated with environmental or social factors. Our study evaluates how variation in edaphic environments and in social factors influences manioc diversity among five ethnic groups of the Amazon region of Colombia. Inventories of landraces, genetic analysis of manioc diversity, visits to farmers’ swiddens and interviews with farmers were carried out during two years of field work. Morphotypic and genotypic diversity of manioc were large. The different ethnic groups of our study cultivate different sweet and bitter manioc landraces which they select and maintain in accordance with their ancestral rules and norms. Differences in available environments among indigenous communities (such as the presence of different soils) did not markedly affect manioc morphotypic or genotypic diversity, while social factors considerably influenced observed manioc diversity. Manioc diversity was explained by two parallel processes of manioc diversification: volunteer seedling selection and manioc seed exchange. We argue that, for a full understanding of manioc diversity, indigenous knowledge, as well as morphological and genetic variation should be taken into account.
Diversity2014, 6(4), 771-791; doi:10.3390/d6040771 - published 5 December 2014 Show/Hide Abstract
Abstract: Regional studies of biotic communities are important for characterising their normal spatial and temporal variation, but there are few such studies of tropical streams. This paper describes changes in invertebrate communities in Yuccabine Creek, a seasonal upland rainforest stream in tropical Australia, over three-year and decadal periods. Invertebrate abundance, richness and evenness were temporally stable, except after major drying or wet-season flows, from which they recovered quickly; however, three wet seasons contrasted in abundance patterns. Species’ responses to flood or drought varied depending on life-histories and habitat dynamics. Communities showed contrasts between wet, early-dry and late-dry seasons, with different characteristic species. Current velocity, leaf litter and substratum particle size were the main environmental correlates with species abundances and multivariate scores. Between-decade contrasts were due to antecedent rainfall and loss of canopy cover. Trophic composition varied seasonally, driven by abundances of predators and detritivores. Yuccabine Creek differs from comparable temperate streams in its high diversity of invertebrates, continual recruitment and spring-dominated continual leaf fall; and from some other tropical streams in its seasonal flow regime. Interpretation of invertebrate metrics in these streams needs to account for historical, antecedent and current conditions, but biannual samples would adequately characterise the fauna.