Search Results (5)

Major threats to biodiversity are climate change, habitat fragmentation (in particular, habitat loss), pollution, invasive species, over-exploitation, and epidemics. Over the last decades habitat fragmentation has been given special attention. Many factors are causing biological systems to extinct; therefore, many issues remain poorly understood. In particular, we would like to know more about the effect of the strength of inter-site coupling (e.g., it can represent the speed with which species migrate) on species extinction or persistence in a fragmented habitat consisting of sites with randomly varying properties. To address this problem we use theoretical methods from mathematical analysis, functional analysis, and numerical methods to study a conceptual single-species spatially-discrete system. We state some simple necessary conditions for persistence, prove that this dynamical system is monotone and we prove convergence to a steady-state. For a multi-patch system, we show that the increase of inter-site coupling leads to the formation of clusters—groups of populations whose sizes tend to align as coupling increases. We also introduce a simple one-parameter sufficient condition for a metapopulation to persist. Full article

Holothuria leucospilota and Stichopus chloronotus are among the most widespread tropical sea cucumber species usually harvested for food and medicine in Asian countries, for which natural stocks have collapsed worldwide. Both species can reproduce sexually and asexually, and a better understanding of their reproductive strategy can provide useful information for conservation purposes. To describe the genetic structure and diversity of sympatric populations from these species in space and time, individuals were sampled over different sites and seasons in Reunion Island (Southwestern Indian Ocean). They were genotyped using 24 and 9 specific microsatellite markers for H. leucospilota and S. chloronotus, respectively. Multi-locus genotypes (MLG) and lineages (MLL) were identified, and analyses of population structure were performed among sites and seasons. No repeated MLG nor MLL were found for H. leucospilota, demonstrating the absence of asexual reproduction. Populations of H. leucospilota were not genetically differentiated, acting as a metapopulation, with larval exchanges within the reef. Contrarily, repeated MLGs were found for S. chloronotus and all populations were genetically differentiated. Asexual reproduction seems to reach a high level for this species (mean clonal richness = 0.24). For both species, genetic structure was stable through seasons. Thus, these sympatric fissiparous sea cucumber species use two different strategies of reproduction, which may allow them to reduce interspecific competition. Full article

Habitat fragmentation is recognized as the most serious threat to biodiversity worldwide and has been the focus of intensive research for a few decades. Due to the complexity of the problem, however, there are still many issues that remain poorly understood. In particular, it remains unclear how species extinction or persistence in a fragmented habitat consisting of sites with randomly varying properties can be affected by the strength of inter-site coupling (e.g., due to migration between sites). In this paper, we address this problem by means of numerical simulations using a conceptual single-species spatially-discrete system. We show how an increase in the inter-site coupling changes the population distribution, leading to the formation of persistence domains separated by extinction domains. Having analysed the simulation results, we suggest a simple heuristic criterion that allows one to distinguish between different spatial domains where the species either persists or goes extinct. Full article

Storms and wind damage are the main cause of biomass loss in forests of Northern Europe, as well as they are synergic with the disturbances causing intense water and temperature stress. This highlights the necessity for climate-smart management at landscape level coupling ecological demands of forestry species with their wind resistance. Silver birch (Betula pendula Roth.), which is highly plastic species, appears to be promising for a wider application under such conditions, as it is believed to tolerate wide range of weather conditions. Though silver birch can be sensitive to water deficit and windthrow, local information on its wind tolerance in sites with different moisture regimes is advantageous. Mechanical stability of 71 mid-aged silver birches (Betula pendula Roth.) growing in seven dry (Hylocomiosa) and five periodically waterlogged (Myrtilloso-sphagnosa) sites with mineral soils in Latvia (hemiboreal lowland conditions) were assessed by the destructive static pulling tests. Site type had a significant, yet intermediate effect on the stability of silver birch. As expected, trees under periodically waterlogged conditions were more prone to collapse under static loading, however, they showed a better resistance to primary failure (beginning of wood structure deformation). Uprooting was the most common form of tree collapse. Surprisingly, considering similar root depths, stem breakage was more frequent in the periodically waterlogged than dry sites (21.9 vs. 5.1%, respectively), indicating high loading resistance of roots, supporting high plasticity and wind resistance of the studied metapopulation of silver birch. Nevertheless, in the periodically waterlogged sites, the difference between forces needed to cause primary and secondary (collapse) failures of stem decreased with age/size, implying necessity for optimization of rotation length. Accordingly, quantification of wind resistance can aid climate-smart selection of species for forest regeneration depending on landscape, suggesting birch as wind resistant option under periodically waterlogged conditions. Full article

Over-exploitation of natural resources can have profound effects on both ecosystems and their resident human populations. Simple theoretical models of the dynamics of a population of human harvesters and the abundance of a natural resource being harvested have been studied previously, but relatively few models consider the effect of metapopulation structure (i.e., a population distributed across discrete patches). Here we analyze a socio-ecological metapopulation model based on an existing single-population model used to study persistence and collapse in human populations. Resources grow logistically on each patch. Each population harvests resources on its own patch to support population growth, but can also harvest resources from other patches when their own patch resources become scarce. We show that when populations are allowed to harvest resources from other patches, the peak population size is higher, but subsequent population collapse is significantly accelerated and across a broader parameter regime. As the number of patches in the metapopulation increases, collapse is more sudden, more severe, and occurs sooner. These effects persist under scenarios of asymmetry and inequality between patches. Our model makes simplifying assumptions in order to facilitate insight and understanding of model dynamics. However, the robustness of the model prediction suggests that more sophisticated models should be developed to ascertain the impact of metapopulation structure on socio-ecological sustainability. Full article