Dynamic spatio-temporal patterns of metapopulation occupancy in patchy habitats

Spatio-temporal dynamics in habitat suitability and connectivity among mosaics of heterogeneous wetlands are critical for biological diversity and species persistence in aquatic patchy landscapes. Despite the recognized importance of stochastic hydroclimatic forcing in driving wetlandscape hydrological dynamics, linking such effects to emergent dynamics of metapopulation poses significant challenges. To fill this gap, we propose here a dynamic stochastic patch occupancy model (SPOM), which links parsimonious hydrological and ecological models to simulate spatio-temporal patterns in species occupancy in wetlandscapes. Our work aims to place ecological studies of patchy habitats into a proper hydrologic and climatic framework to improve the knowledge about metapopulation shifts in response to climate-driven changes in wetlandscapes. We applied the dynamic version of the SPOM (D-SPOM) framework in two wetlandscapes in the US with contrasting landscape and climate properties. Our results illustrate that explicit consideration of the temporal dimension proposed in the D-SPOM is important to interpret local- and landscape-scale patterns of habitat suitability and metapopulation occupancy. Our analyses show that spatio-temporal dynamics of patch suitability and accessibility, driven by the stochasticity in hydroclimatic forcing, influence metapopulation occupancy and the topological metrics of the emergent wetlandscape dispersal network. D-SPOM simulations also reveal that the extinction risk in dynamic wetlandscapes is exacerbated by extended dry periods when suitable habitat decreases, hence limiting successful patch colonization and exacerbating metapopulation extinction risks. The proposed framework is not restricted only to wetland studies but could also be applied to examine metapopulation dynamics in other types of patchy habitats subjected to stochastic external disturbances.

Stochastic Spatiotemporal Patterns of Metapopulation Occupancy in Dynamic Wetlandscapes

<p>Dynamic internal feedbacks and stochastic external shocks drive the spatial organization and heterogeneity of patchy habitats, and thus the temporal variability of patch suitability and accessibility. Such spatiotemporal shifts impact species dispersal among patches and metapopulation persistence. Here, we extended the widely recognized concepts of patch-occupancy and metapopulation capacity from static to dynamic patchy habitats, with isolated wetlands embedded in uplands as the case study. We present a new metapopulation modeling approach by linking a hydrological model for wetland variability with a dynamic stochastic patch-occupancy model. In two case study wetlandscapes, we evaluate (1) spatiotemporal dynamics of wetland hydrologic regimes, and patch suitability and connectivity driven by stochastic hydroclimatic forcing, and (2) spatiotemporal patterns of patch occupancy and metapopulation dispersal dynamics. Our modeling results reveal the importance of specific connected patches that serve as persistent hubs and form the backbone of dispersal corridors to support species dispersal in fragmented dynamic landscapes. Our analyses reveal that the interplay between stochastic hydroclimatic forcing and patchy habitat structure could drive species to extinction when specific thresholds are crossed.</p>

Population density of the eastern pygmy-possum in a heath–woodland habitat

The eastern pygmy-possum (Cercartetus nanus) has posed a challenge in attempts to describe its population density due to low rates of capture, preference for patchy habitats and periodic influxes of subadult individuals. We conducted a mark–recapture study of this species using a grid of nest boxes in a 9-ha patch of banksia heath–woodland. We captured 54 adults across the two years of our study. We estimated the density of adult pygmy-possums to be 1.5–4.2 ha–1 from different population models. This is substantially lower than previous estimates in equivalent habitat because we focussed on adults and recognised that they were not confined to the area bounded by our grid. We captured 36 subadults over the two years but they could not be reliably modelled due to extremely low recapture rates, which reflect high rates of dispersal and also mortality. For this reason, only the number of adults should be used to characterise populations of this species. Further study is required to investigate population dynamics over time and to describe the density of eastern pygmy-possums in other habitats.