Addressing the problem of scale that emerges with habitat fragmentation

Abstract

Fragmentation and scale Although habitat loss has well‐known impacts on biodiversity, the effects of habitat fragmentation remain intensely debated. It is often argued that the effects of habitat fragmentation, or the breaking apart of habitat for a given habitat amount, can be understood only at the scale of entire landscapes composed of multiple habitat patches. Yet, fragmentation also impacts the size, isolation and habitat edge for individual patches within landscapes. Addressing the problem of scale on fragmentation effects is crucial for resolving how fragmentation impacts biodiversity. Scaling framework We build upon scaling concepts in ecology to describe a framework that emphasizes three “dimensions” of scale in habitat fragmentation research: the scales of phenomena (or mechanisms), sampling and analysis. Using this framework, we identify ongoing challenges and provide guidance for advancing the science of fragmentation. Implications We show that patch‐ and landscape‐scale patterns arising from habitat fragmentation for a given amount of habitat are fundamentally related, leading to interdependencies among expected patterns arising from different scales of phenomena. Aggregation of information when increasing the grain of sampling (e.g., from patch to landscape) creates challenges owing to biases created from the modifiable areal unit problem. Consequently, we recommend that sampling strategies use the finest grain that captures potential underlying mechanisms (e.g., plot or patch). Study designs that can capture phenomena operating at multiple spatial extents offer the most promise for understanding the effects of fragmentation and its underlying mechanisms. By embracing the interrelationships among scales, we expect more rapid advances in our understanding of habitat fragmentation.

Landscape experiments unlock relationships among habitat loss, fragmentation, and patch‐size effects

“…What are the mechanisms driving the effects in these experiments? There are several hypothesized mechanisms for the effects of habitat fragmentation and these mechanisms can operate at different scales (Fahrig et al, 2019; Fletcher Jr. et al, 2023). Previous results from Experiment 1 revealed that movement of C. vittiger was impeded with aggregated loss, leading to effects on local reproduction (Fletcher Jr., Reichert, & Holmes, 2018; Poli et al, 2020).…”

“…Yet we expected that species with greater dispersal capacities would show weaker responses to habitat fragmentation than the poorer dispersers. In general, we expected that patch-scale responses would be consistent with landscape-scale responses, due to the interdependence of habitat patterns across scales (Fletcher Jr. et al, 2023). Despite this potential consistency, we expected that patch size alone would be helpful but not sufficient for predicting landscape-scale effects of habitat loss and fragmentation due to landscape-scale processes not being captured.…”

“…The breaking apart of habitat for a given habitat amount can generate a variety of interdependent patterns in remaining habitat (Fletcher Jr. et al, 2023). Some of the earliest uses of the term “fragmentation” envisioned that fragmentation increased when the number of patches was greater because habitat was more “broken up” (Moore, 1962).…”

“…Yet patches in a landscape can also vary in the degree of how broken apart or separated they are based on the relative isolation of remaining patches (Saura, 2021), an aspect of fragmentation related to what Fahrig (2017) described as “habitat clumpiness”. Taken together, two key components of fragmentation can be envisioned: habitat subdivision based on the number of patches for a given habitat amount (and as a corollary, the mean patch size and proportion of edge; Fletcher Jr. et al, 2023) and the relative isolation of remaining habitat (Figure 1a; Goodwin & Fahrig, 2002; Grez et al, 2004). Across scales, these components of fragmentation can be confounded with other key patterns of habitat loss and patch characteristics.…”

“…Patch‐size effects on species occurrence are widely reported (Bender et al, 1998; Prugh et al, 2008) and, if habitat is broken apart into multiple patches in landscapes for a given habitat amount, then the mean patch size of fragmented landscapes must decline (Fletcher Jr. et al, 2023). Despite this fundamental relationship, it has been argued that patch‐size effects do not provide relevant information for understanding landscape‐scale effects of habitat loss and fragmentation (Fahrig et al, 2019).…”