The rate of species extinction in declining or fragmented ecological communities

Loss of habitat can take many forms, ranging from the fragmentation of once-continuous habitat to the slow erosion of populations across continents. Usually, the harm leading to biodiversity loss is not immediately obvious: there is an extinction debt. Most modelling research of extinction debt has focussed on relatively rapid losses of habitat with species loss happening in response afterwards. In this paper, using a niche-orientated community model we compare and contrast two different mechanisms and find contrasting patterns of extinction debt. From small fragments, we typically see the rapid initial loss of many species, followed by a slower loss of species on larger timescales. When we consider slow incremental declines of population sizes, we find initially a slow rate of extinction which subsequently increases exponentially. In such cases, the delayed extinctions may go undetected initially both because the extinctions may be small relative to background randomness and because rate itself is not constant and takes time to reach its maximum.

Automated summary

Loss of habitat can have various forms, such as habitat fragmentation and gradual decline of populations. Extinction debt, where species loss occurs after habitat loss, is not immediately apparent. This study investigates two mechanisms using a niche-oriented community model and reveals different patterns of extinction debt. Rapid initial loss of species followed by slower loss over time is observed in small fragments, while slow decline in population sizes initially leads to a low extinction rate that increases exponentially afterwards.