Patterns of bird functional diversity on land‐bridge island fragments

Abstract

Summary1. The loss of species diversity due to habitat fragmentation has been extensively studied. In contrast, the impacts of habitat fragmentation on functional diversity remains relatively poorly understood. We conducted bird functional diversity studies on a set of 41 recently isolated land-bridge islands in the Thousand Island Lake, China. 2. We analysed differences in bird species richness and a recently developed suite of complementary functional diversity indices (FRic, volume of functional space occupied; FEve, evenness of abundance distribution in the functional trait space; FDiv, divergence in the distribution of abundance in the trait volume) across different gradients (island area and isolation). 3. We found no correlations between FRic and FEve or FEve and FDiv, but negative correlations between FRic and FDiv. As predicted, island area accounted for most of the variation in bird species richness, whereas isolation explained most of the variation in species evenness (decreasing species evenness with increasing isolation). Functional diversity appears to be more strongly influenced by habitat filtering as opposed to limiting similarity. More specifically, across all islands, both FRic and FEve were significantly lower than expected for randomly assembled communities, but FDiv showed no clear patterns. FRic increased with island area, FEve decreased with island area and FDiv showed no clear patterns. 4. Our finding that FEve decreases with island area at TIL may indicate low functional stability on such islands, and as such large islands and habitat patches may deserve extra attention and/or protection. These results help to demonstrate the importance of considering the effects of fragmentation on functional diversity in habitat management and reserve design plans.

Habitat fragmentation and biodiversity conservation: key findings and future challenges

“…A suite of studies, focusing on both plant and animal communities, have shown that island area plays the dominant role in controlling community recovery on TIL's islands. On the species and gene levels, plant, bird, snake, and small mammal communities have clear relationships with island area, but not island isolation (Wang et al 2010(Wang et al , 2011(Wang et al , 2012bHu et al 2011;Zhang et al 2012;Ding et al 2013;Si et al 2014Si et al , 2015aSu et al 2014;Yuan et al 2015). There are some notable exceptions to the trend of area effects dominating isolation effects (e.g., Wang et al 2012a;Yu et al 2012;Peng et al 2014).…”

Bird Functional Traits Respond to Forest Structure in Riparian Areas Undergoing Active Restoration

“…Birds have high mobility at moderate spatial scales [62], so that the small spatial scale of our study enabled to isolate the effect of forest structure from the effects of spatial barriers to bird dispersal to sites under restoration. Forest structure can have strong effects on their avian assemblage composition [17,35].…”

Bird assemblage vulnerability depends on the diversity and biogeographic histories of islands

“…Functional evenness, functional divergence, and functional richness (45) were calculated using the R package FD (46), based on the functional trait values for all birds on each island (the position of each species on axis 1 and axis 2 of the PCA summary of bill morphology, tarsus length, and body size). These traits were chosen because they are commonly used indicators of resource use and energy constraints (body size) (47,48), and foraging behavior in birds (bill morphology and tarsus length) (41,42). SR for each island was calculated using the land birds on each island.…”