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

Abstract

Biodiversity is widely acknowledged to influence the magnitude and stability of a large array of ecosystem properties, with biodiverse systems thought to be more functionally robust. As such, diverse systems may be safer harbors for vulnerable species, resulting in a positive association between biodiversity and the collective vulnerability of species in an assemblage, or “assemblage vulnerability.” We find that, for 35 islands across Northern Melanesia, bird assemblage vulnerability and biodiversity are positively associated. This relationship is highly contingent on Pleistocene connectivity, suggesting that biogeographic history—a factor often overlooked in biodiversity and ecosystem-functioning studies—may influence contemporary ecological processes. In the face of biodiversity loss attributable to anthropogenic drivers, reduced ecosystem functioning may erode the safe harbors of vulnerable assemblages. Paradoxically, these results suggest that biodiverse systems, as more robust systems, may experience greater biodiversity loss over ecological time because they harbor more vulnerable species accumulated over evolutionary time.

Predicting ecosystem vulnerability to biodiversity loss from community composition

“…While this low potential for functional compensation is often attributed to a lack of community redundancy, and is consistent with studies that suggest a positive relationship between ecosystem vulnerability and the presence of unique species (Mouillot et al 2013, Ricotta et al 2016, our results suggest that unique species should mainly affect ecosystem vulnerability when that species is also among the most vulnerable. Although studies quantifying vulnerability properties beyond the species scale are rare, some evidence suggests a positive relationship between biodiversity and total community vulnerability , which could be mediated by increasing trait variance (Mouillot et al 2013, Weeks et al 2016). Thus, collecting information on trait distributions and covariance, and evaluating communities using an ecosystem stress test could improve estimates of ecosystem vulnerability.…”

“…5) How well do community-scale vulnerability properties (sensu Weeks et al 2016) predict ecosystem vulnerability? 2) How does trophic structure influence compensation outcomes, and consequently, ecosystem vulnerability?…”

Patterns and drivers of fish extirpations in rivers of the American Southwest and Southeast

“…Our findings are critical, as we need to understand impending extinctions among river basins worldwide that have many threatened native species (Arthington, Dulvy, Gladstone, & Winfield, ; Jelks et al., ; Vörösmarty et al., ). Further understanding of how extirpation risk among native fish species may vary among regions with different levels of biodiversity (e.g., Weeks et al., ) is needed to enhance global species conservation.…”

“…However, presence of dams disproportionately affected extirpation risk of species isolated in upland streams of the ACF and of flowdependent species in the ACT (Table 1) wide that have many threatened native species (Arthington, Dulvy, Gladstone, & Winfield, 2016;Jelks et al, 2008;V€ or€ osmarty et al, 2010). Further understanding of how extirpation risk among native fish species may vary among regions with different levels of biodiversity (e.g., Weeks et al, 2016) is needed to enhance global species conservation.…”

“…Mounting evidence suggests that environmental change is the cause of biologic communities being disassembled (i.e., altered) according to spatially and temporally heterogeneous rates of species losses (Zavaleta et al, 2009). Changes in species composition, rather than systematic reductions in species richness, appear more common (Dornelas et al, 2014), and regions with high biodiversity may support the persistence of threatened species (Weeks, Gregory, & Naeem, 2016). Traits-based approaches have proven powerful for understanding species-specific reductions in native and increases in non-native species ranges (Olden, Poff, & Bestgen, 2006), and responses to changing riverine conditions, including alterations in flow regimes (Mims & Olden, 2013) and land use practices (Moore & Olden, 2017).…”