The Three Gorges Dam in China is the largest dam ever built. Its impacts on the biodiversity and ecological processes in the region are causing concern to ecologists worldwide. The dam and associated environmental alterations may result in a number of regional changes in terrestrial and aquatic biodiversity, as well as in ecosystem structure and functioning. The dam may also provide a rare opportunity for a grand-scale experiment in habitat fragmentation, allowing ecologists to develop and test a series of hypotheses concerning the dynamics of biodiversity and biotic communities and their responses to disturbances. Such research can help improve conservation practices, stimulate international collaborations, and promote public education on the environment.

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The Three Gorges Dam: an ecological perspective

: Under extreme (>80%) levels of habitat loss and fragmentation, exponentially increasing risks of extinction have been predicted; however, the proportion of species that will decline is uncertain. Factors influencing species declines include patch characteristics, such as size and condition, and species' ecological traits, such as dispersal ability. In central New South Wales, Australia, 90% of the mallee woodland has been cleared for agriculture. At each of three 100-km2 locations, we sampled beetles in 10 sites and asked: (1) How is the impact of habitat loss and fragmentation mediated by remnant condition and size? (2) What proportion of the beetle fauna is declining? (3) Are ecological traits based on body size, trophic group, flight, and position relative to the ground correlated with beetle responses to habitat loss and fragmentation? Seven of 34 beetle species (21%) occurred in fragmented and isolated populations in the agricultural landscape, implying that they may be at risk of local extinction. Most declining species depended on large remnants, but two species were confined to disturbed linear remnants, emphasizing the importance of diverse management regimes for invertebrate conservation. In contrast, approximately one-quarter of the beetle fauna survived in paddocks and so was not at risk of decline. Greatest species richness was observed in narrow linear remnants, not square reserves, because of the influx of species from the matrix and the presence of strip-specialist species. Flying ability and position explained most of the variation in species responses to fragmentation. Flightless species or species living underground were most vulnerable to decline in agricultural landscapes. Combinations of traits were also implicated in beetle responses, however, suggesting that causal mechanisms involve more than just the effects of flight or position. To identify species vulnerable to decline in fragmented landscapes, then, many traits need to be considered simultaneously.




Resumen: Bajo niveles extremos (>80%) de perdida y fragmentacion de habitat, se han previsto riesgos de extincion que incrementan exponencialmente; sin embargo, la proporcion de especies que declinaran es incierta. Los factores que influyen en la declinacion de especies incluyen caracteristicas del parche, como tamano y condicion, y los atributos ecologicos de las especies, como habilidad dispersora. En el centro de New South Wales, Australia, 90% del bosque se ha desmontado para agricultura. En cada una de tres localidades de 10 km2, muestreamos escarabajos en 10 sitios y preguntamos (1) ??Como intervienen el tamano y condicion del remanente en el impacto de la perdida de habitat y fragmentacion? (2) ?Que proporcion de la fauna de escarabajos esta declinando? (3) ?Estan correlacionados los atributos ecologicos basados en tamano corporal, grupo trofico, suelo y posicion en relacion con el suelo con las respuestas de escarabajos a la perdida y fragmentacion de habitat? Siete de 34 especies (21%) ocurrieron en poblaciones fragmentadas y aisladas en el paisaje agricola, implicando que pueden estar en riesgo de extincion local. La mayoria de las especies declinantes dependian de remanentes extensos, pero dos especies estaban confinadas a remanentes perturbados lineales, lo que enfatiza la importancia de diversos regimenes de manejo para la conservacion de invertebrados. En contraste, aproximadamente la cuarta parte de la fauna de escarabajos sobrevivio en dehesas y no estuvieron en riesgo de declinar. Se observo la mayor riqueza de especies en remanentes lineales angostos y no en reservas cuadradas debido al influjo de especies de la matriz y a la presencia de especies especialistas de franjas. La habilidad de volar y la posicion explicaron la mayor parte de la variacion en las respuestas de especies a la fragmentacion. Especies no voladoras o especies subterraneas fueron mas vulnerables a la declinacion en paisajes agricolas. Sin embargo, combinaciones de atributos tambien estuvieron implicadas en respuestas de escarabajos, lo que sugiere que los mecanismos causales implican mas que solo los efectos de vuelo o posicion. Por lo tanto, para identificar especies vulnerables a la declinacion en paisajes fragmentados se deben considerar muchos atributos simultaneamente.

Beetle responses to habitat fragmentation depend on ecological traits, habitat condition, and remnant size

Assessing the influence of Environmental Impact Assessments on science and policy: an analysis of the Three Gorges Project.

Mega hydropower projects in tropical forests pose a major emergent threat to terrestrial and freshwater biodiversity worldwide. Despite the unprecedented number of existing, under-construction and planned hydroelectric dams in lowland tropical forests, long-term effects on biodiversity have yet to be evaluated. We examine how medium and large-bodied assemblages of terrestrial and arboreal vertebrates (including 35 mammal, bird and tortoise species) responded to the drastic 26-year post-isolation history of archipelagic alteration in landscape structure and habitat quality in a major hydroelectric reservoir of Central Amazonia. The Balbina Hydroelectric Dam inundated 3,129 km2 of primary forests, simultaneously isolating 3,546 land-bridge islands. We conducted intensive biodiversity surveys at 37 of those islands and three adjacent continuous forests using a combination of four survey techniques, and detected strong forest habitat area effects in explaining patterns of vertebrate extinction. Beyond clear area effects, edge-mediated surface fire disturbance was the most important additional driver of species loss, particularly in islands smaller than 10 ha. Based on species-area models, we predict that only 0.7% of all islands now harbor a species-rich vertebrate assemblage consisting of ≥80% of all species. We highlight the colossal erosion in vertebrate diversity driven by a man-made dam and show that the biodiversity impacts of mega dams in lowland tropical forest regions have been severely overlooked. The geopolitical strategy to deploy many more large hydropower infrastructure projects in regions like lowland Amazonia should be urgently reassessed, and we strongly advise that long-term biodiversity impacts should be explicitly included in pre-approval environmental impact assessments.

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Widespread Forest Vertebrate Extinctions Induced by a Mega Hydroelectric Dam in Lowland Amazonia

Land clearing depletes and fragments habitat, resulting in the loss of biodiversity. Corridors of native vegetation can ameliorate the impacts of land clearing by reducing isolation of remnant vegetation. However the effectiveness of linear remnants as corridors or connecting habitat is influenced by remnant size and condition. In central New South Wales, Australia, 84–95% of native vegetation has been cleared, with remnants occurring as isolated reserves and interconnecting strips beside roads and paddocks. Do the linear remnants provide connectivity throughout the landscape for reptile populations? In three 100-km2 agricultural locations, I classified all remnants into one of 10 “landscape elements” based on shape, management, and vegetation. I used generalized linear models and permutation tests to examine differences in reptile abundance among landscape elements. Only two blind snakes were captured in paddocks, suggesting that the matrix between remnants is virtually devoid of reptiles. Remnant shape ...

J.F. Villiers

Papers

Ecological changes in recent land-bridge islands in French Guiana, with emphasis on vertebrate communities