Fragmentation per-se and biodiversity may form a unimodal patter
Conservation ecologists consider habitat fragmentation as one of the major threats to biodiversity. However, the phenomenon of fragmentation involves three different effects – habitat loss, decreased average patch size and increased average isolation between patches. While habitat loss always exists when an area is damaged by human activity, the two other effects take place only when habitat fragmentation occurs (hereafter, Fragmentation Per-Se effects). Consequently, to understand the influence of fragmentation on biodiversity, one should consider only the two FPS effects after removing the effect of habitat loss. My aims are: 1. To present four methods to decouple habitat loss from the FPS effects; 2. To show empirical results from our works regarding the effect of FPS on various taxonomic groups; 3. To suggest a new hypothesis regarding the relationship between FPS and biodiversity.
Using up to four methods to decouple habitat loss from the FPS effects -- Saturation Index, SLOSS Index, SAR Exploration and Fisher’s Alpha Index of diversity -- in a highly heterogeneous and fragmented landscape, we show that FPS does not affect (beetles), or increases (spiders), species diversity. Additionally, our theoretical (simulation model) and experimental (coral reef fish) studies show that increased isolation may elevate species diversity. These studies demonstrate that various processes, such as competitive release and low predation pressure, mediated by isolation intensity, may enhance between-patch variation and consequently contribute to higher diversity. I argue that contemporary spatial-oriented ecological theories and hypotheses support the idea that FPS has positive effects on species diversity at low and moderate levels of fragmentation. In turn, I propose that FPS and biodiversity form a unimodal pattern where biodiversity increases till a certain level of fragmentation and thereafter decreases due to increased extinction probability of small and very isolated populations.