Extinction debt on reservoir land-bridge islands

Abstract

13 14Large dams cause extensive inundation of habitats, with remaining terrestrial habitat confined to 15 highly fragmented archipelagos of land-bridge islands comprised of former hilltops. Isolation of 16 biological communities on reservoir islands induces local extinctions and degradation of remnant 17 communities. "Good practice" dam development guidelines propose using reservoir islands for 18 species conservation, mitigating some of the detrimental impacts associated with flooding terrestrial 19 habitats. The degree of species retention on islands in the long-term, and hence, whether they are 20 effective for conservation is currently unknown. Here, we quantitatively review species' responses to 21 isolation on reservoir islands. We specifically investigate island species richness in comparison with 22 neighbouring continuous habitat, and relationships between island species richness and island area, 23 isolation time, and distance to mainland and to other islands. Species' responses to isolation on 24 reservoir islands have been investigated in only 15 of the >58 000 large-dam reservoirs (dam height 25 >15 m) operating globally. Research predominantly originates from wet tropical forest habitats and 26 focuses on mammals, with species richness being the most widely-reported ecological metric. 27Terrestrial taxa are, overall, negatively impacted by isolation on reservoir islands. Reservoir island 28 species richness declines with isolation time, and although the rate of loss is slower on larger islands, 29 all islands exhibit depauperate species richness <100 years after isolation, compared to continuous 30 mainland habitats. Such a pattern of sustained and delayed species loss following large-scale habitat 31 disturbance is indicative of an extinction debt existing for reservoir island species: this pattern is 32 evident across all taxonomic groups and dams studied. Thus, reservoir islands cannot reliably be used 33 for species conservation as part of impact mitigation measures, and should instead be included in area 34 calculations for land impacted by dam creation. Environmental licensing assessments as a 35 precondition for future dam development should explicitly consider the long-term fate of island 36 communities when assessing biodiversity loss vs energy output. 37 38

The geometry of habitat fragmentation: Effects of species distribution patterns on extinction risk due to habitat conversion

“…In landscapes with rapid landscape change and high matrix mortality, temporal data could be used to disentangle geometric and demographic effects. While short-term responses of species and communities at the landscape scale will primarily reflect geometric effects, long-term effects will be caused by demographic changes (Helm, Hanski, & Pärtel, 2006;Jones, Bunnefeld, Jump, Peres, & Dent, 2016;Kuussaari et al, 2009).…”

Connectivity with primary forest determines the value of secondary tropical forests for bird conservation

“…In summary, SF avian communities are at least partially dependent on contiguous PF source populations. If connected PF populations have low species richness, then SF will likely never develop the bird communities associated with extensive PF forest stands (Ferraz et al., ; Jones et al., ; Stouffer et al., ). However, if SF sites are adjacent to extensive PF, forest specialists may recolonize relatively rapidly.…”

“…In addition, bird species occurring in isolated SF embedded within a non‐forest matrix may be more sensitive to random population fluctuations and local extinction. Connectivity to PF is an important factor in SF recovery, and the species composition of bird communities in isolated SF may never fully converge with that of PF (Jones, Bunnefeld, Jump, Peres, & Dent, ; Wolfe et al., ).…”

Effect of Site Attributes and Matrix Composition on Neotropical Primate Species Richness and Functional Traits: A Comparison Among Regions

“…Another possible reason could be pet-keeping and hunting, as carnivorous and insectivorous primates are represented mainly by Cebids, which are frequently used for those purposes (e.g., Cebus capucinus, Saguinus nigricollis, and Saguinus leucopus as pets; and Cebus kaapori and Sapajus xanthosternos as hunting targets) [101][102][103][104][105]. Although empirical evidence exists to support the idea of negative effects of reservoirs (the main type of water body in our study areas) on primates and other vertebrates [106,107], the negative relationship between area of water bodies in the matrix and diets based in animal prey may also be explained by a negative effect of water bodies on prey species. Invertebrates are the main prey fed upon by Neotropical primates [74], and they are also sensitive to dams and alterations in water flow [108,109].…”