Biology subjects

Cushman, S. A.

Publications and source records attributed to Cushman, S. A..

3 recordsLinked to original sources

bioRxiv2025

Landscape matters: Deriving a generalizable understanding of population connectivity using empirical data and graph theory

O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/674386v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@1226384org.highwire.dtl.DTLVardef@b3949eorg.highwire.dtl.DTLVardef@1e24ae0org.highwire.dtl.DTLVardef@1a1c773_HPS_FORMAT_FIGEXP M_FIG C_FIG Human impacts on ecosystems have accelerated globally, driving a 10% decline in terrestrial biodiversity and a 70% decline in wildlife populations over the past five decades. These losses are closely linked to habitat modification and fragmentation, highlighting the urgent need for management strategies grounded in a clear understanding of how wildlife use landscapes and navigate human-altered areas. Connectivity between populations is critical for species persistence and is shaped by the interplay between landscape features and species movement. Most connectivity studies pursue application-focused goals, such as designing corridors or assessing land-use effects, often targeting single species within specific landscapes. While these approaches provide depth, they limit the development of general principles that apply across species and regions. Graph theory offers a powerful framework to distill complex connectivity patterns into comparable metrics, creating opportunities to identify such generalities. In this study, we examined connectivity patterns for 11 Indian carnivore species distributed across heterogeneous landscapes. Using secondary data, we developed habitat networks from species distribution models that incorporated both habitat quality and matrix resistance. We then applied graph theory to generate networks based on connectivity between identified habitat nodes, enabling comparisons across species and landscapes. Our results show that while connectivity patterns differ markedly among species, broad trends emerge. Larger-bodied species like tigers, which in our study are often threatened species, can overcome the effects of fragmentation better than smaller bodied species, however their connectivity is dependent on the existence of high-quality patches. Fragmented and heterogenous landscapes were always associated with modular, less efficient networks irrespective of the species. Importantly, landscape characteristics had greater influence on network-level connectivity properties, while species traits more strongly determined node-level structural complexity of the network. By integrating network theory with multispecies analyses across diverse landscapes, our work moves beyond single-species case studies to identify general drivers of connectivity. In terms of conservation, our approach allows us to generate broad insights into drivers of population connectivity informing strategies for lesser-known species and guide more effective, landscape-scale management in an era of rapid environmental change.

ecology↗

bioRxiv2021

Macrosystem community assembly patterns are predicted by foundation tree species genetic connectivity and environment across the American Southwest

Macrosystems ecology is an emerging science that aims to integrate traditionally distinct disciplines to predict how hierarchical interacting processes influence the emergence of complex patterns across local to regional and global scales. Despite increased focus on cross-scale relationships and cross-disciplinary integration, few macroecology studies incorporate genetic-based processes. Here we used a community genetics approach to investigate the pattern-process relationships underlying the emergence of macroscale biodiversity patterns. We tested the hypothesis that environmental variation, geography, and genetic connectivity in a foundation tree species differentially predict associated community assembly patterns from local to continental scales. Using genome-wide SNP data, we assessed genetic connectivity as a function of genetic similarity and structure in Fremont cottonwood (Populus fremontii) across its distribution throughout the southwestern US and Mexico. For the same trees, we measured community composition, diversity, and abundance of leaf modifying arthropods and sequenced targeted amplicons of twig fungal endophytes. Five key findings emerged. (1) We identified three primary and six secondary population genetic groups within P. fremontii, which occupy distinct climate niches. (2) Both the leaf modifying arthropod and fungal endophyte communities were significantly differentiated across host tree ecotypes, with genetic distance among sampling locations explaining 13-17% of respective macroscale community structure. (3) For arthropods, environmental distance was the strongest driver of community similarity. (4) Conversely, host genetic connectivity was the most important contributor to macroscale endophyte community structure, with no significant contribution of environmental distance. (5) Furthermore, we observed a shift in the strength of interspecific relationships, with host genetics most strongly influencing associated communities at the intermediate population scale. Our findings suggest that genetic connectivity and environmental variation play integrated roles in macroscale community assembly, and their relative importance changes with scale. Thus, conservation genetic management of the diversity harbored within foundation species is vital for sustaining associated regional biodiversity.

ecology↗

bioRxiv2017

The role of hybridization during ecological divergence of southwestern white pine (Pinus strobiformis) and limber pine (P. flexilis)

Interactions between extrinsic factors, such as disruptive selection, and intrinsic factors, such as genetic incompatibilities among loci, can contribute to the maintenance of species boundaries. The relative roles of these factors in the establishment of reproductive isolation can be examined using species pairs characterized by gene flow throughout their divergence history. We investigated the process of speciation and the maintenance of species boundaries between Pinus strobiformis and P.flexilis. Utilizing ecological niche modeling, demographic modeling, and genomic cline analyses, we illustrated a history of divergence with continuous gene flow between these species. We found an abundance of advanced generation hybrids and a lack of loci exhibiting large allele frequency differences across the hybrid zone. Additionally, we found evidence for climate-associated variation in the hybrid index and niche divergence between parental species and the hybrid zone. Our results are consistent with extrinsic factors, such as climate, being an important isolating mechanism for these species. A buildup of intrinsic incompatibilities and of co-adapted gene complexes is also apparent in our results, although these appear to be in the earliest stages of development. This supports previous work in coniferous species demonstrating the importance of extrinsic factors in creating and enforcing species boundaries. Overall, we lend support to the hypothesis that varying strengths and directions of selection pressures across the long lifespans of conifers, in combination with their life history strategies, delay the evolution of strong intrinsic incompatibilities.

evolutionary biology↗