Abstract
My research aimed to examine a variety of macroecological and biogeographical patterns using a large number of purely habitat island datasets (i.e. isolated patches of natural habitat set within in a matrix of human land uses) sourced from both the literature and my own sampling, with the objective of testing various macroecological and biogeographical patterns. These patterns can be grouped under four broad headings: 1) species–area relationships (SAR), 2) nestedness, 3) species abundance distributions (SADs) and 4) species incidence functions (function of area). Overall, I found that there were few hard macroecological generalities that hold in all cases across habitat island systems. This is because most habitat island systems are highly disturbed environments, with a variety of confounding variables and ‘undesirable’ species (e.g. species associated with human land uses) acting to modulate the patterns of interest. Nonetheless, some clear patterns did emerge. For example, the power model was by the far the best general SAR model for habitat islands. The slope of the island species–area relationship (ISAR) was related to the matrix type surrounding archipelagos, such that habitat island ISARs were shallower than true island ISARs. Significant compositional and functional nestedness was rare in habitat island datasets, although island area was seemingly responsible for what nestedness was observed. Species abundance distribution models were found to provide useful information for conservation in fragmented landscapes, but the presence of undesirable species substantially affected the shape of the SAD. In conclusion, I found that the application of theory derived from the study of true islands, to habitat island systems, is inappropriate as it fails to incorporate factors that are unique to habitat islands.
Highlights
This is not to say that traditional island theory is unsuitable in the context of habitat islands; the interplay between immigration and extinction is a primary determinant of richness dynamics in habitat islands, for instance
Increasingly many rainforest landscapes have been fragmented by the creation of dams and reservoirs, resulting in the flooding of the surrounding landscape, and the creation of patches of forest surrounded by a matrix of water. Strictly speaking these fragments are true islands in that they are surrounded by water (Whittaker and Fernández-Palacios 2007), but in many ways the islands are more akin to habitat islands, such as in terms of the dominant assembly processes and sizes of the islands
These questions included: what is the best model/functional form of island Species–area relationship (SAR) in habitat islands (Matthews et al 2015b)? Is there a threshold habitat island area below which the form of the ISAR changes (Matthews et al 2014b)? Do habitat generalist species act to modulate the shape of the ISAR (Matthews et al 2014c)? How do island species–area relationships (ISARs; i.e. the number of species occurring within each of a set of islands plotted against the area of each isolate) differ from species accumulation curves (SACs; i.e. plots of increasing cumulative species number with sampling effort; Whittaker and Matthews 2014)?
Summary
It has become increasingly realised that habitat islands differ from true islands in many ways (Watling and Donnelly 2006, Laurance 2008), for example in terms of the surrounding matrix, edge effects, habitat connectivity and the main processes driving community assembly (see Laurance 2008). Increasingly many rainforest landscapes have been fragmented by the creation of dams and reservoirs, resulting in the flooding of the surrounding landscape, and the creation of patches of forest surrounded by a matrix of water Strictly speaking these fragments are true islands in that they are surrounded by water (Whittaker and Fernández-Palacios 2007), but in many ways the islands are more akin to habitat islands, such as in terms of the dominant assembly processes and sizes of the islands. I aim to determine whether (a) there are any general rules/ patterns regarding species’ distributions in habitat islands, and (b) it is possible to derive any information which can benefit biodiversity management and conservation in patchy landscapes
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