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

Abstract

Disentangling the multiple factors controlling species diversity is a major challenge in ecology. Island biogeography and environmental filtering are two influential theories emphasizing respectively island size and isolation, and the abiotic environment, as key drivers of species richness. However, few attempts have been made to quantify their relative importance and investigate their mechanistic basis. Here, we applied structural equation modelling, a powerful method allowing test of complex hypotheses involving multiple and indirect effects, on an island‐like system of 22 French Guianan neotropical inselbergs covered with rock‐savanna. We separated the effects of size (rock‐savanna area), isolation (density of surrounding inselbergs), environmental filtering (rainfall, altitude) and dispersal filtering (forest‐matrix openness) on the species richness of all plants and of various ecological groups (terrestrial versus epiphytic, small‐scale versus large‐scale dispersal species). We showed that the species richness of all plants and terrestrial species was mainly explained by the size of rock‐savanna vegetation patches, with increasing richness associated with higher rock‐savanna area, while inselberg isolation and forest‐matrix openness had no measurable effect. This size effect was mediated by an increase in terrestrial‐habitat diversity, even after accounting for increased sampling effort. The richness of epiphytic species was mainly explained by environmental filtering, with a positive effect of rainfall and altitude, but also by a positive size effect mediated by enhanced woody‐plant species richness. Inselberg size and environmental filtering both explained the richness of small‐scale and large‐scale dispersal species, but these ecological groups responded in opposite directions to altitude and rainfall, that is positively for large‐scale and negatively for small‐scale dispersal species. Our study revealed both habitat diversity associated with island size and environmental filtering as major drivers of neotropical inselberg plant diversity and showed the importance of plant species growth form and dispersal ability to explain the relative importance of each driver.

Multi‐scale biogeographic controls over plant communities on granite outcrops in the Southwest Australian Floristic Region

“…This supports conclusions made by Henneron et al . (2019) and Yates et al . (2019), whereby outcrop area may be less important for biodiversity persistence across such ancient landscapes.…”

“…In the theory of environmental filtering, local abiotic conditions can impede species survival and persistence, and also indirectly filter the species pool by affecting biotic interactions and dispersal (Henneron et al . 2019). This supports conclusions made by Henneron et al .…”

Artificial refuges to combat habitat loss for an endangered marsupial predator: How do they measure up?

“…Many animals often select natural refuges close to important resources that provide protection, temperature regulation, or food (Bretscher, Dittel, Lambert, & Adler, 2018; Croak et al, 2012). Northern quolls in the Pilbara often inhabit complex rocky habitat, likely because it provides protection from predation (Cook, 2010; Hernandez‐Santin et al, 2016) and fire (Burrows, Ward, & Robinson, 2009), and often contains temporary ponds and sheltered crevices (Henneron, Sarthou, De Massary, & Ponge, 2019; Radford, Gibson, Corey, Carnes, & Fairman, 2015). Artificial dens in our study area were usually placed in open, flat landscapes, with a history of disturbance—characteristics that have been shown to negatively affect refuge use in other species (Lalas, Jones, & Jones, 1999; McGregor et al, 2014).…”

Habitat amount and ambient temperature dictate patterns of anuran diversity along a subtropical elevational gradient

“…Areas corresponding to more extensive natural vegetation are more likely to harbour a higher diversity of suitable (micro)habitats and thereby confer a higher chance of accommodating habitat specialist species (Henneron et al., 2019; Leibold et al., 2004). Many frog species are considered habitat specialists and their local occupancy depends exclusively on some environmental conditions.…”