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

Aim: To test whether the species richness of understorey insectivorous birds on forest islands induced by a major hydroelectric dam is best explained by either the island biogeography theory (IBT) or the habitat amount hypothesis (HAH). Given the low dispersal ability of the focal species group and the hostile water matrix, we predict that the species richness will be predominantly driven by an island effect as posited by the IBT, rather than a sample area effect as posited by the HAH. Location: Forest islands within the Balbina Hydroelectric Reservoir, central Brazilian Amazonia. Taxon: Birds. Methods: We mist-netted birds at 33 forest islands (0.63–1,699 ha), totalling 874 individuals of 59 species. The size of the local landscape used to calculate the habitat amount was determined by a multi-scale analysis in which buffers around mist-net lines ranged from 50 to 2,000 m. We applied four tests to examine whether the species richness on forest islands is predominantly driven by either an island effect (island size) or a sample area effect (habitat amount). Results: From the four tests applied, one was consistent with an island effect, two were regarded as inappropriate to test the HAH, and one could not be adequately addressed due to island size being highly correlated with habitat amount in the local landscape (200-m buffer). Main conclusions: Some of the proposed ways of testing the HAH may lead to misleading conclusions. The relative importance of island size in determining the species richness of understorey insectivorous birds on forest islands is higher than that of surrounding habitat amount, thereby providing stronger support for IBT. We propose a conceptual framework, based on the degree of matrix permeability and species dispersal ability, to determine to what extent a patch- or landscape-centric worldview in landscape ecology provides the most appropriate framework to assess the effects of habitat fragmentation on biodiversity

Vertebrate community disassembly in human-induced Amazonian forest islands

The extent to which land-use change impairs tropical biodiversity is controversial. This is because while some species may thrive in human-modified landscapes, others are locally extirpated – the so-called “few winners and many losers” paradigm. Furthermore, reliable environmental impact assessments imply that the correct drivers of biodiversity change are recognised, and suitable reference conditions are available. Herein, I examine vertebrate responses to habitat fragmentation induced by two mega hydroelectric reservoirs in Brazilian Amazonia. In the Tucuruí Hydroelectric Reservoir, bird point count surveys were carried out on 36 forest islands in 2006 and 2007. In the Balbina Hydroelectric Reservoir, I carried out bird mist-net surveys on 33 forest islands and five continuous forest sites in 2015 and 2016; I also used autonomous recording units to survey anuran species on 74 forest islands and four continuous forest sites in 2015. At Tucuruí, bird species traits associated with vulnerability to forest fragmentation included rarity and forest dependency. At Balbina, species richness of understorey insectivorous birds was more affected by island size than the amount of habitat surrounding mist-net lines, indicating that a patch-centric approach is most appropriate to measure species responses to habitat loss if species exhibit low dispersal ability and the surrounding habitat matrix is hostile. Regarding environmental impact assessments, the higher the intactness of the reference condition, the greatest the estimated impact of habitat fragmentation on bird species richness. In other words, studies of biodiversity responses to land-use change will likely yield over-optimistic results if they are masked by the low conservation status of either degraded or insufficiently large habitat patches regarded as the reference condition. Finally, island size per se played a decisive role in explaining anuran species richness on Amazonian forest islands, yet the inferential power of island species-area relationships is only reliable if derived from an appropriate study design

Sampling design may obscure species–area relationships in landscape-scale field studies

We investigated 1) the role of area per se in explaining anuran species richness on reservoir forest islands, after controlling for several confounding factors. We also assessed 2) how sampling design affects the inferential power of island species–area relationships (ISARs) aiming to 3) provide guidelines to yield reliable estimates of area-induced species losses in patchy systems. We surveyed anurans with autonomous recording units at 151 plots located on 74 islands and four continuous forest sites at the Balbina Hydroelectric Reservoir landscape, central Brazilian Amazonia. We applied semi-log ISAR models to assess the effect of sampling design on the fit and slope of species–area curves. To do so, we subsampled our surveyed islands following both a 1) stratified and 2) non-stratified random selection of 5, 10, 15, 20 and 25 islands covering 1) the full range in island size (0.45–1699 ha) and 2) only islands smaller than 100 ha, respectively. We also compiled 25 datasets from the literature to assess the generality of our findings. Island size explained ca half of the variation in species richness. The fit and slope of species–area curves were affected mainly by the range in island size considered, and to a very small extent by the number of islands surveyed. In our literature review, all datasets covering a range of patch sizes larger than 300 ha yielded a positive ISAR, whereas the number of patches alone did not affect the detection of ISARs. We conclude that 1) area per se plays a major role in explaining anuran species richness on forest islands within an Amazonian anthropogenic archipelago; 2) the inferential power of island species–area relationships is severely degraded by sub-optimal sampling designs; 3) at least 10 habitat patches spanning three orders of magnitude in size should be surveyed to yield reliable species–area estimates in patchy systems

Protecting forests at the expense of native grasslands: Land-use policy encourages open-habitat loss in the Brazilian cerrado biome

The agricultural conversion of natural habitats is one of the main drivers of biodiversity loss worldwide. In the ∼2 million km2 Brazilian cerrado biome, a global biodiversity hotspot, vast areas have been converted into croplands and cattle pastures. Because the cerrado biome is overwhelmingly contained within private lands, Brazil's environmental legislation should serve as a decisive instrument in protecting these natural ecosystems. We assessed the role of Legal Reserves (LRs), legally defined as the minimum proportion of private landholdings set aside to protect natural vegetation, in the conservation of the cerrado biome. We assume that the property-scale allocation of LRs is primarily based on economic decision-making, creating a bias against cerrado protection. We therefore assessed the area ratio between forest vegetation (FV) and grassland vegetation (GV) areas across LRs within 48,762 landholdings, 9 formal protected areas (PAs) and 34 Indigenous Lands (ILs) within the cerrado (sensu lato) of the 903,357-km2 state of Mato Grosso, Brazil. We show that there are 7.26 ha of forest lands for each hectare of native grasslands within private RLs of the cerrado biome within Mato Grosso, a ratio almost three-fold larger than that found in formal PAs and ILs. ILs protect in absolute values (hectares) six-fold more native grassland vegetation than PAs. We discuss the policy relevance of this severe land-use bias in maintaining the heterogeneity of cerrado habitats for biodiversity conservation within private properties, which account for 90% of the entire cerrado biome

Using relict species-area relationships to estimate the conservation value of reservoir islands to improve environmental impact assessments of dams

Large dams are emerging drivers of landscape-scale habitat fragmentation, causing extensive flooding and transforming hilltops into islands. Environmental Impact Assessments (EIAs; the process to assess and account for impacts of development) do not explicitly consider reservoir islands in calculations of habitat impacted by dam construction. Reservoir islands maintain relict biological communities from the previously continuous habitat. Relict communities are subject to an extinction debt whereby species are lost over time. We demonstrate how estimating the ‘conservation value’ of islands (CV; the proportion of relict continuous habitat [forest] species on islands) using relict species–area relationships (RSARs), can be used in an area-of-impact correction tool to account for insular habitats in EIAs. We used data from eight taxonomic groups within the Balbina Hydroelectric Reservoir (BHR) archipelago in Brazilian Amazonia. We found ca. 72,000 ha of insular habitat had reduced CV, equating to 60% of aggregate island area, and that an additional 24% of the ca. 300,000 ha BHR water surface area should be included in area assessments for impacted terrestrial habitat. Where reservoir island creation is unavoidable, using RSARs to assess the CV of islands enables more accurate and dynamic assessment of the ecological impacts of dam construction

Distribuição de aves de sub-bosque ao longo de gradientes ambientais na Amazônia central

Riparian zones are recognized by their importance to maintaining the regional biodiversity. Several studies compared the bird distribution between riparian and non-riparian zones to evaluate the conservation value of riparian zones. However, no study aimed to establish how wide is the riparian zone recognized by birds in relation to distance from the stream. We investigated the distribution of understory birds along the environmental gradients of distance from the stream, clay content and slope of the terrain in a terra firme central Amazonian forest. We sampled understory birds using mist nets in 45 plots, sampling each plot three times. We used Non-metric Multidimensional Scaling (NMDS) to reduce the data dimensionality of species quantitative (abundance) and qualitative (presence-absence) composition in one multivariate axis. In 9720 mist-net hours, we captured 1506 birds belonging to 98 species in 28 families. Estimation of the width of riparian zone as indicated by understory birds in Reserva Ducke depended on the community attribute considered: species quantitative composition (100 m), species qualitative composition (140 m). The species distribution was related to clay content, but it was not related to slope of the terrain. In Reserva Ducke, distance from the stream is correlated with clay content, but it is not correlated with slope of the terrain. Clay content affects the plant species composition, which in turn could affect the bird species composition. However, the distribution pattern of birds in places near to and away from the stream is consistent among the studies carried out in diverse geomorphologies in both temperate and tropical regions, indicating an effect of distance from the stream itself. The protection of strip s adjacent to streams is one of the most used conservation strategies. In Brazil, the protected strip around the stream extends to 30 m. We demonstrated that the width of the protected strip should be increased considerably for the Brazilian environmental legislation to be effective in fulfilling its role of protecting the biodiversity associated with the riparian zones.Zonas ripárias são reconhecidas pela sua importância na manutenção da biodiversidade regional. Diversos estudos compararam a distribuição de aves em zonas ripárias e não-ripárias a fim de avaliar o valor para conservação das zonas ripárias. Contudo, nenhum estudo se dedicou a estabelecer até que distância em relação ao riacho as aves reconhecem como ripária. Nós investigamos a distribuição de aves de sub-bosque ao longo dos gradientes ambientais de distância do riacho, conteúdo de argila e inclinação do terreno em uma floresta de terra firme na Amazônia central. Para amostrar a comunidade de aves de sub-bosque, utilizamos redes de neblina em 45 parcelas, sendo cada parcela amostrada três vezes. Utilizamos Non-metric Multidimensional Scaling (NMDS) para reduzir a dimensionalidade dos dados de composição quantitativa (abundância) e qualitativa (presença-ausência) de espécies em um eixo de ordenação multivariada. Em 9720 horas-rede, nós capturamos 1506 aves pertencentes a 98 espécies em 28 famílias. A estimativa da largura da zona ripária indicada pelas aves de subbosque na Reserva Ducke dependeu do atributo da comunidade considerado: composição quantitativa (100 m), composição qualitativa (140 m). A distribuição de espécies esteve relacionada com o conteúdo de argila, mas não esteve relacionada com a inclinação do terreno. Na Reserva Ducke, distância do riacho apresenta correlação com o conteúdo de argila, mas não apresenta correlação com inclinação do terreno. Conteúdo de argila afeta a composição de espécies vegetais, que, por sua vez, pode afetar a composição de aves. Contudo, o padrão de distribuição de aves em locais próximos e afastados do riacho é consistente entre estudos realizados em diversas geomorfologias, tanto em regiões temperadas quanto em regiões tropicais, o que indica um efeito da distância do riacho per se. A proteção de faixas adjacentes a riachos constitui umas das estratégias de conservação mais utilizadas. No Brasil, a faixa protegida ao redor do riacho se estende até 30 m. Nós demonstramos que a faixa protegida deve ser aumentada consideravelmente para que a legislação ambiental brasileira seja eficiente em cumprir o seu papel de proteger a biodiversidade associada a zonas ripárias

The width of riparian habitats for understory birds in an Amazonian forest

Riparian habitats are important for the maintenance of regional biodiversity. Many studies have compared bird distributions between riparian and non-riparian habitats but have not established how wide riparian habitats used by birds are, as measured by distance from the nearest stream. We investigated the distribution of understory birds along gradients of distance from streams, soil clay content, and slope in a central Amazonian forest, by mistnetting birds three times in 45 plots. We used nonmetric multidimensional scaling (NMDS) to reduce the dimensionality of species quantitative (abundance) and qualitative (presence- absence) composition to one multivariate axis. Estimates of the width of riparian habitats as indicated by understory birds depended on the community attribute considered, measuring 90 m for species quantitative composition and 140 m for species qualitative composition. Species distributions were correlated with clay content but were independent of slope, while distance from streams was positively correlated with clay content but independent of slope. Clay content affects plant species composition, which in turn, may influence bird species composition. However, distribution patterns of birds in relation to distance from streams are consistent among studies carried out in many different temperate and tropical regions, indicating an effect of distance from streams itself. Protection of riparian habitats is one of the most widely used conservation strategies, and Brazilian environmental legislation mandates the protection of a 30 m wide strip of riparian vegetation on either side of small streams. We show that the protected strip should be much wider and recommend strategies to place other forms of land protection contiguous with riparian areas so that Brazilian environmental legislation better fulfills its role of protecting biodiversity associated with riparian habitats. © 2012 by the Ecological Society of America