Species–area relationships and extinctions caused by habitat loss and fragmentation

Abstract

The species-area relationship (SAR) has been used to predict the numbers of species going extinct due to habitat loss, but other researchers have maintained that SARs overestimate extinctions and instead one should use the endemics-area relationship (EAR) to predict extinctions. Here, we employ spatially explicit simulations of large numbers of species in spatially heterogeneous landscapes to investigate SARs and extinctions in a dynamic context. The EAR gives the number of species going extinct immediately after habitat loss, but typically many other species have unviable populations in the remaining habitat and go extinct soon afterwards. We conclude that the EAR underestimates extinctions due to habitat loss, the continental SAR (with slope~0.1 or somewhat less) gives a good approximation of short-term extinctions, while the island SAR calculated for discrete fragments of habitat (with slope~0.25) predicts the long-term extinctions. However, when the remaining area of land-covering habitat such as forest is roughly less than 20% of the total landscape and the habitat is highly fragmented, all current SARs underestimate extinction rate. We show how the 'fragmentation effect' can be incorporated into a predictive SAR model. When the remaining habitat is highly fragmented, an effective way to combat the fragmentation effect is to aggregate habitat fragments into clusters rather than to place them randomly across the landscape.

Species–fragmented area relationship

“…1 shows the results of spatially explicit simulations of a large number of ecologically dissimilar species inhabiting a heterogeneous landscape (ref. 26 and SI Text). In the example in Fig.…”

“…We used a lattice-based stochastic patch occupancy model (26) to simulate spatially explicit dynamics of large numbers of species with dissimilar ecological traits. The model assumes that different lattice cells may represent different habitat type, and that habitat type across the lattice may be spatially correlated (26). In the present simulations, we assumed a high degree of spatial correlation in habitat type (parameter ω = 2 in ref.…”

“…This creates a problem: Habitat loss is virtually always accompanied by fragmentation (22)(23)(24), and hence the remaining habitat is not contiguous, unlike assumed by SAR, at the landscape level. In other words, SAR does not account for any adverse effects of fragmentation on the occurrence of species (25,26). Fragmentation matters whenever individual habitat fragments are small enough to reduce the viability of the respective local populations (27,28).…”

Using avian functional traits to assess the impact of land-cover change on ecosystem processes linked to resilience in tropical forests

“…The resulting loss and degradation of primary forests typically reduces species richness, and increases biological homogenization, across a wide range of taxonomic groups [7][8][9][10][11]. However, it is becoming increasingly clear that the raw number and even heterogeneity of species surviving in communities may be poor indices of functional aspects of biodiversity [12,13], including the trophic interactions needed to maintain recruitment and gene flow in rainforest trees [14,15].…”

Segmentação multiresolução variográfica ótima.

“…A destruição e a fragmentação de habitats como consequência da expansão urbana e agrícola, são apontados como os principais fatores responsáveis pela perda global de biodiversidade (TILMAN, 2001;RYBICKI;HANSKI, 2013;RAMIADANTSOA et al, 2015). Com a crescente demanda agropecuária muitas áreas próximas a regiões protegidas tem se tornado um mosaico de plantações e pastagens, promovendo uma inevitável perda e fragmentação das regiões de floresta (LIRA et al, 2012).…”