Habitat fragmentation and extinction thresholds on fractal landscapes

Habitat fragmentation is a potentially critical factor in determining popul ation persistence. In this paper, we explore the effect of fragmentation wh en the fragmentation follows a fractal pattern. The habitat is divided into patches, each of which is suitable or unsuitable. Suitable patches are eit her occupied or unoccupied, and change state depending on rates of coloniza tion and local extinction. We compare the behaviour of two models: a spatia lly implicit patch-occupancy (PO) model and a spatially explicit cellular a utomaton (CA) model. The PO model has two fixed points: extinction, and a s table equilibrium with a fixed proportion of occupied patches. Global extin ction results when habitat destruction reduces the proportion of suitable p atches below a critical threshold. The PO model successfully recreates the extinction patterns found in other models. We translated the PO model into a stochastic cellular automaton. Fractal arrangements of suitable and unsui table patches were used to simulate habitat fragmentation. We found that: ( i) a population on a fractal landscape can tolerate more habitat destructio n than predicted by the patch-occupancy model, and (ii) the extinction thre shold decreases as the fractal dimension of the landscape decreases. These effects cannot be seen in spatially implicit models. Landscape structure pl ays a vital role in mediating the effects of habitat fragmentation on persi stence.