Islands, mainland, and terrestrial fragments: How isolation shapes plant diversity

Abstract

The fragmentation of natural habitats is a major threat for biodiversity. However, the impact and spatial scale of natural isolation mechanisms leading to species loss, compared to anthropogenic fragmentation, are not clear, mainly due to differences between fragments and islands, such as matrix permeability. We studied a 500 km2 Mediterranean region in France, including urban habitat fragments, continuous habitat, and continental‐shelf islands. On the basis of 295 floristic relevés, we built species–area relationships to compare isolation in fragments after urbanization, with continuous habitat and continental‐shelf islands. We assumed either no dispersal, infinite dispersal, or estimated intermediate levels of habitat reachability through graph theory. Isolation mechanisms occurred in fragments but with a lower strength than in near‐shore islands, and most importantly affected perennial plants. Annual plants were less affected, probably due to their smaller size and shorter life cycle. Isolation occurred at landscape level in fragments and at patch level in islands. The amount of reachable habitat (accounting for spatial configuration) explained local species richness in both systems, but the amount of habitat (no consideration of spatial configuration) was already a good predictor. These results suggest an important role of habitat amount around fragments in mitigating the isolation effects observed in near‐shore islands, and the importance of carefully considering different functional groups.

Extinction–immigration dynamics lag behind environmental filtering in shaping the composition of tropical dry forests within a changing landscape

“…Furthermore, immigration still depended on habitat amount in forest interior communities, indicating that this relationship did not only concern edge vicinity. Therefore, in line with recent works on plant communities (Martín‐Queller et al , MacDonald et al ), our study supports more the HAH (i.e. habitat amount determines immigration, Fahrig ) than the ETIB.…”

Habitat amount, not patch size and isolation, drives species richness of macro‐moth communities in countryside landscapes

“…Predictions of the habitat amount hypothesis were upheld for rare reptiles and one frog species in an agricultural landscape in New South Wales, Australia (Pulsford, Lindenmayer, & Driscoll, ). Habitat amount, without considering spatial configuration, was already a good predictor for local species richness of plants in a Mediterranean region of France including urban habitat (Martín‐Queller, Albert, Dumas, & Saatkamp, ). In an eighth study, avian species richness in southern Ontario, Canada, responded primarily to habitat amount and negligibly to fragmentation (De Camargo, Boucher‐Lalonde, & Currie, ).…”

Habitat diversity associated to island size and environmental filtering control the species richness of rock‐savanna plants in neotropical inselbergs

“…Understanding the multiple determinants regulating species diversity has long been a major theme in ecology, in particular within the fields of island biogeography and community ecology (MacArthur andWilson 1967, Leibold et al 2004). Plant species richness of vegetation patches has been shown to increase with patch area (Connor and McCoy 1979, Honnay et al 1999, Van Noordwijk et al 2015, patch heterogeneity (Huston 1999, Dufour et al 2006, habitat amount (Lindgren and Cousins 2017), disturbance (Pickett 1980, Lavorel et al 1994, mildness of the environment (Gray 1989, Fonty et al 2009, Cheng et al 2013, resource availability (Neri et al 2017), size of regional species pools (Zobel 1997), and to decrease with patch isolation (Gadgil 1971, Hanski 1991, Martín-Queller et al 2017. Those drivers of species richness could potentially have interactive effects and tradeoffs can exist among them (Allouche et al 2012).…”

“…H 3b : Larger altitude at the top of inselberg increases the diversity of epiphytes by promoting long fog periods, and of large-scale dispersal (anemochorous) species by enhancing downslope winds, but it reduces the diversity of small-scale dispersal (autochorous) species due to steeper inselberg slopes (Obregon et al 2011). H 4 : Higher openness of the surrounding forest matrix increases the diversity of inselberg plant species by increasing permeability to immigration from the surroundings (Martín-Queller et al 2017).…”