The contribution of theory and experiments to conservation in fragmented landscapes

Abstract

The clearing and fragmentation of terrestrial ecosystems is commonly acknowledged as a major cause of the decline of biodiversity. These and other predicted responses to habitat fragmentation are derived from theory, which ecologists have tested with empirical approaches ranging from observations to experimental manipulations. These empirical approaches have also identified areas of theory in need of additional development. For example, experimental studies of fragmentation have provided insights such as the key role played by the matrix surrounding fragments, the importance of edge effects, and the impacts of corridors linking fragments with one another. Much less clear, however, is the extent to which these theoretical and empirical studies – while advancing our conceptual understanding of ecological responses to landscape change – help guide management and conservation practice. We review lessons learned from landscape-scale fragmentation experiments and observational studies, present the results of a survey of fragmentation and conservation experts which probed for links and mismatches between fragmentation studies and conservation practice, and discuss how future studies can contribute to conservation practice. Our survey showed that respondents consider fragmentation theory and empirical studies and their findings important for guiding conservation and management practices. The survey also identified that there are disconnects between what is typically studied by fragmentation ecologists and factors that are central to the practice of biodiversity conservation, notably, community-based human dimensions (e.g. economic, social, health issues), policy and governance, ecosystem services, eco-evolutionary responses of species, and interaction of multiple threats to biodiversity and ecosystem processes. We discuss how these disconnects can present opportunities for experiments to continue to provide valuable recommendations for conservation practice in fragmented landscapes

Experimental evidence does not support the Habitat Amount Hypothesis

“…Other effects of fragmentation, including varying combinations of fragment area, edge, matrix quality, and isolation, are known to drive changes in species diversity (Didham et al ). Consistent with applied conservation (Resasco et al ), our results also emphasize the importance of connectivity, the value of prioritizing habitat and corridors for connectivity (Pascual‐Hortal and Saura ), and configuring landscapes to reduce habitat isolation (Gilbert‐Norton et al ). We advocate for research that focuses on understanding mechanisms that impact species diversity and ecosystem processes in fragmented landscapes above and beyond habitat amount.…”

Evolution of dispersal strategies and dispersal syndromes in fragmented landscapes

“…Habitat conversion from natural ecosystems to agriculture, forestry and human settlements has taken over large amounts of land, leaving species with an increasingly shrinking world (Foley et al , Newbold et al ). Beyond direct negative effects on taxonomic, functional and genetic diversity (Foley et al , Newbold et al ), this indirectly erodes biodiversity through the fragmentation of large, continuous habitats into smaller isolated patches in a sea of often heterogeneous matrix (Fahrig , Haddad et al , Wilson et al , Resasco et al , Thompson et al ). Fragmentation modifies landscapes in four ways – reducing habitat quantity; increasing the number of patches; decreasing their size; and, increasing isolation (Fahrig ) – with diverse effects on population dynamics.…”

Landscape‐specific thresholds in the relationship between species richness and natural land cover

“…First, intensive land use in the matrix may act on thresholds. Landscapes with more intensive matrix land use are characterized by harsher edges, reduced permeability, greater exposure to threats, and provide fewer supplemental resources to those provided by matrices characterized by lower intensity land use (Deikumah, McAlpine, & Maron, ; Koh & Ghazoul, ; Prevedello & Vieira, ; Resasco, Bruna, Haddad, Banks‐Leite, & Margules, ; Swift & Hannon, ; Watson, Whittaker, & Freudenberger, ). As these factors could compound the adverse effect of fragmentation (e.g., edge effects), we hypothesize that landscapes with more intensive land use will have a higher threshold value.…”