Species’ movement influence responses to habitat fragmentation

Aim

Human conversion of land leads to habitat loss and fragmentation. The effects of habitat loss are well-established, but the effects of fragmentation beyond those of habitat loss, “fragmentation per se” (FPS), are intensely debated. One area of debate is how different species might respond to FPS. We will answer whether FPS have more negative effects on species that spend more time in the matrix and less on species with higher potential patch encounter rates.

Location

Virtual landscapes.

Methods

We simulated the effects of FPS on multiple species with different movement characteristics. All species moved with a random walk (RW), a correlated RW (CRW), or a habitat-dependent walk (HDW). Species also had increasing habitat bias which caused individuals to have a higher probability of moving into a more suitable habitat. The walk type modified the rate at which species encountered habitat patches. Increased bias caused individuals to spend more time in suitable habitats and less time in the matrix between patches. All species experienced higher mortality in less suitable habitats. We analysed FPS effects on species for whom the fragmented focal habitat was the most suitable.

Results

With bias, the species diversity of RW species declined with FPS, while FPS had little effect on the species diversity of species moving by CRW. For HDW species, spending less time in the matrix (moderate movement bias) caused species diversity to increase with FPS, but to decline with high bias.

Main conclusions

These results suggest that even for species that are dependent on fragmented habitat, FPS does not have a unidirectional effect. FPS can have a positive effect on species with high patch encounter rates (HDW with moderate bias) as their functional connectivity increases. These results help to explain why different studies show contradictory effects of FPS on biodiversity.