Fragmentation, grazing and the species–area relationship

Abstract

Habitat loss is one of the greatest threats to species persistence. Gauging the scale of this problem requires quantitative methods that can predict the number of extinctions resulting from habitat loss. For the past three decades, the species–area relationship, an empirical relationship between the number of species present in an area and the size of that area, has been this tool. However, it fails to incorporate threats to species aside from habitat loss and the heterogeneous distribution of these threats across habitats. Recent studies have improved species–area predictions by incorporating not only direct effects of area on richness, but also indirect effects of area (through area‐mediated predator abundance), on prey species richness. We extend this work to test the hypotheses that the indirect effects of the multiple threats of grazing and trampling in addition to fragmentation will amplify the effect of area on species richness and that this effect will be greatest in zones closest to the fragment edge. Further, we test for species and population level effects of fragmentation and grazing, including the non‐random pattern of species loss and the decline in population sizes. We test our hypotheses with a field study of land snail richness in fragments with and without the additional threats of grazing and trampling. Our study supports the hypotheses that fragments with multiple threats in addition to habitat loss harbour fewer species than fragments without these threats, and that this effect is non‐uniform across fragments, populations and species.

Avian malaria in introduced, native and endemic New Zealand bird species in a mixed ecosystem

“…Many New Zealand bird populations are critically endangered (Hitchmough et al 2007) and efficient wildlife management strategies have been employed (Craig et al 2000) to safeguard their long-term viability and sustain them as essential functional components of the terrestrial ecosystems. Ongoing predation and habitat changes since European settlement in New Zealand have contributed to population declines in many bird species (O'Donnell 1996;Bogich et al 2012) even in those still not considered at risk. For example, New Zealand robins (Petroica longipes) (henceforth NZ robins) are currently considered to be 'not threatened' (Robertson et al 2013), despite the IUCN reporting a decreasing population trend for this species (IUCN 2014).…”

A question of adaptability: Climate and habitat change lower trait diversity in butterfly communities in south-western Germany

“…However, additional nutritional import in the form of faeces might favour nitrophilic plant species. As a result of trampling there are likely to be smaller populations in grazed habitats, and this in combination with habitat fragmentation could have resulted in an increase in the loss of species (Bogich et al, 2011). We found neither positive nor additional negative effects of grazing on butterfly communities in our study.…”

The Effect of Forest Fragmentation on Tree Species Abundance and Diversity in the Eastern Arc Mountains of Tanzania

“…It also interacts synergistically with anthropogenic threats (Laurance, 2007) interrupting species occurrence, composition and density (Stoms and Estes, 1993). Literature shows that habitat fragmentation also condenses habitat area coverage enhancing the species extinction debt (Bogich et al, 2012). By reducing the total habitat area requirements of species (Murcia, 1995;Fahrig, 2003;Echeverría et al, 2007), the rate of species extinction and endemism is enhanced http://www.aloki.hu • .…”