Non-random lizard extinctions in land-bridge Amazonian forest islands after 28 years of isolation

Abstract

Major hydropower infrastructure has become a leading driver of biodiversity loss in the lowland tropics. Terrestrial species typically become stranded in post-isolation land-bridge islands within hydroelectric reservoirs. Understanding the resulting extinction dynamics of insular communities is critical to inform, if not to avert, the ongoing blitzkrieg of dam development. Here we assess the effects of forest patch and landscape metrics on diurnal lizard species richness and composition within the Balbina Hydroelectric Dam and surrounding areas in the Central Brazilian Amazon. This 28-yr-old dam created a reservoir of ~ 4438 km2, comprising 3546 islands. We sampled 25 of these islands (0.83–1466 ha) and five mainland continuous forest sites, one of which placed along stream banks. We further related morpho-ecological traits and the geographic distribution of lizard species to the spatial metrics of islands where they occurred. Using 100 L-pitfall traps operated over 5447 trap-days, we recorded 1123 lizards from 17 taxa, two of which exclusively found along stream banks within continuous forest. Island area was the best predictor of species richness and composition. Small islands (≤ 2 ha) harboured fewer than a third of all species typically observed in larger islands and continuous forest (≥ 8 species), and only islands ≥ 100 ha retained nearly complete lizard faunas. Lizard assemblages inhabiting small, isolated islands consisted almost exclusively of an oversimplified set of widely distributed, large-bodied, habitat generalist, heliophile species associated with open areas and forest edges, and that feed on a wide spectrum of prey sizes. These wholesale changes in lizard community structure were characterized by severe losses in functional traits, and may profoundly affect ecosystem functioning

Bird assemblages on Amazonian river islands: Patterns of species diversity and composition

“…Nested pattern between species‐rich and species‐poor sites was linked to island area, but not to the degree of isolation, suggesting that this system is extinction‐driven rather than colonization‐driven (Bruun & Moen, ). Indeed, differential extinctions explained vertebrate distributions on artificial islands created by fragmentation of continuous forests by hydroelectric dams (Aurélio‐Silva, Anciães, Henriques, Benchimol & Peres, ; Bueno, Dantas, Henriques & Peres, ; Lima et al., ; Palmeirim, Vieira & Peres, ; Si et al., ).…”

Effects of Forest Fragmentation on the Vertical Stratification of Neotropical Bats

“…Yet, due to multiple and often interacting stressors, the region is facing rapid environmental change and since 1970 has lost over 790,000 km 2 (nearly 20%) of its original forest cover [8]. Although habitat loss and fragmentation continue to act as primary threats to the megadiverse Amazonian vertebrate communities [9][10][11], little is known about how their composition and structure across forest strata is affected by habitat modification.With roughly 1400 species globally [12], bats are the second largest mammalian order and account for 25% of the total mammal diversity in the Brazilian Amazon [13,14]. Powered flight allows bats to explore resources across the multilayered space of tropical rainforests and an increasing number of studies have documented changes in species abundance from ground to subcanopy and canopy levels in both the Neo-and Paleotropics (e.g., [15][16][17][18]).…”

“…Yet, due to multiple and often interacting stressors, the region is facing rapid environmental change and since 1970 has lost over 790,000 km 2 (nearly 20%) of its original forest cover [8]. Although habitat loss and fragmentation continue to act as primary threats to the megadiverse Amazonian vertebrate communities [9][10][11], little is known about how their composition and structure across forest strata is affected by habitat modification.…”

Patch‐scale biodiversity retention in fragmented landscapes: Reconciling the habitat amount hypothesis with the island biogeography theory

“…Hence, the degree to which either a patch‐ or landscape‐centric worldview is most pertinent in fragmentation ecology studies should be determined by the species vagility within the local landscape, which is largely a combination of matrix permeability (a landscape attribute) and dispersal ability (a species trait) (Figure ). Accordingly, increasing support for IBT should be expected for a species assemblage with low dispersal ability in patches surrounded by an impermeable matrix (Figure c; this study; Palmeirim et al., ). Conversely, increasing support for HAH would be expected for a species assemblage in which high dispersal ability is prevalent and habitat patches are surrounded by a permeable matrix (Figure b; Melo et al., ).…”

“…As a result, surveyed islands shared relatively low levels of intra‐patch habitat heterogeneity regarding closed‐canopy forest structure. Third, the Balbina islands are isolated by a hostile water matrix which likely hampers the dynamic of colonisation and extinction (Palmeirim, Vieira, & Peres, ), particularly for species that are unable to either cross wide gaps or use dead tree snags as stepping stones. Indeed, the disappearance of understorey insectivorous birds from forest fragments has been largely attributed to dispersal limitation (Şekercioḡlu et al., ), which along with a severely hostile water matrix explain patterns of bird species occupancy on forest islands (Moore, Robinson, Lovette, & Robinson, ).…”