Changes in arthropod assemblages along a wide gradient of disturbance in Gabon.

Searching for indicator taxa representative of diverse assemblages, such as arthropods, is an important objective of many conservation studies. We evaluated the impacts of a wide gradient of disturbance in Gabon on a range of arthropod assemblages representing different feeding guilds. We examined 4 x 10(5) arthropod individuals from which 21 focal taxa were separated into 1534 morphospecies. Replication included the understory of 3 sites in each of 4 different stages of forest succession and land use (i.e., habitats) after logging (old and young forests, savanna, and gardens). We used 3 complementary sampling methods to survey sites throughout the year. Overall differences in arthropod abundance and diversity were greatest between forest and open habitats, and cleared forest invaded by savanna had the lowest abundance and diversity. The magnitude of faunal differences was much smaller between old and young forests. When considered at this local scale, anthropogenic modification of habitats did not result in a monotonous decline of diversity because many herbivore pests and their associated predators and parasitoids were abundant and diverse in gardens, where plant productivity was kept artificially high year-round through watering and crop rotation. We used a variety of response variables to measure the strength of correlations across survey locations among focal taxa. These could be ranked as follows in terms of decreasing number of significant correlations: species turnover > abundance > observed species richness > estimated species richness > percentage of site-specific species. The number of significant correlations was generally low and apparently unrelated to taxonomy or guild structure. Our results emphasize the value of reporting species turnover in conservation studies, as opposed to simply measuring species richness, and that the search for indicator taxa is elusive in the tropics. One promising alternative might be to consider "predictor sets" of a small number of taxa representative of different functional groups, as identified in our study

Changes in arthropod assemblages along a wide gradient of disturbance in Gabon.

Searching for indicator taxa representative of diverse assemblages, such as arthropods, is an important objective of many conservation studies. We evaluated the impacts of a wide gradient of disturbance in Gabon on a range of arthropod assemblages representing different feeding guilds. We examined 4 x 10(5) arthropod individuals from which 21 focal taxa were separated into 1534 morphospecies. Replication included the understory of 3 sites in each of 4 different stages of forest succession and land use (i.e., habitats) after logging (old and young forests, savanna, and gardens). We used 3 complementary sampling methods to survey sites throughout the year. Overall differences in arthropod abundance and diversity were greatest between forest and open habitats, and cleared forest invaded by savanna had the lowest abundance and diversity. The magnitude of faunal differences was much smaller between old and young forests. When considered at this local scale, anthropogenic modification of habitats did not result in a monotonous decline of diversity because many herbivore pests and their associated predators and parasitoids were abundant and diverse in gardens, where plant productivity was kept artificially high year-round through watering and crop rotation. We used a variety of response variables to measure the strength of correlations across survey locations among focal taxa. These could be ranked as follows in terms of decreasing number of significant correlations: species turnover > abundance > observed species richness > estimated species richness > percentage of site-specific species. The number of significant correlations was generally low and apparently unrelated to taxonomy or guild structure. Our results emphasize the value of reporting species turnover in conservation studies, as opposed to simply measuring species richness, and that the search for indicator taxa is elusive in the tropics. One promising alternative might be to consider "predictor sets" of a small number of taxa representative of different functional groups, as identified in our study

Faunal turnover of arthropod assemblages along a wide gradient of disturbance in Gabon

We examined the results of a study in Gamba, Gabon, focusing on the impacts of disturbance on arthropods, including more than 400 000 individuals, from which 21 focal taxa were separated into 1534 morphospecies by parataxonomists. Replication included the understorey of three sites in each of four different stages of forest succession and land use (= 'habitats') after logging (old and young forests, savanna and gardens), surveyed over a whole year with three sampling methods. Generally, there was a good correspondence between the number of species sorted by taxonomists and the number of morphospecies sorted by parataxonomists. Despite higher taxonomic groups being present in most habitats, a large proportion of insect species was site-or habitat-specific. Anthropogenic modification of habitats did not result in a monotonic decline of abundance and diversity, as many herbivore pests and their associated predators and parasitoids invaded gardens, where plant productivity was kept artificially high year-round through watering and crop rotation. Because gardens were colonized mostly by invasive crop pests with little relation with the forest fauna, these results emphasize the concept of maintenance of 'quality biodiversity' and the value of considering other variables than species richness alone in conservation studies. Further, several lines of evidence indicated that savanna habitats at Gamba supported a species-poor arthropod fauna distinct from that in nearby habitats. It is therefore questionable whether in Africa insect assemblages of savanna represent a smaller subset of their neighboring forest fauna

Faunal turnover of arthropod assemblages along a wide gradient of disturbance in Gabon

We examined the results of a study in Gamba, Gabon, focusing on the impacts of disturbance on arthropods, including more than 400 000 individuals, from which 21 focal taxa were separated into 1534 morphospecies by parataxonomists. Replication included the understorey of three sites in each of four different stages of forest succession and land use (= ‘habitats’) after logging (old and young forests, savanna and gardens), surveyed over a whole year with three sampling methods. Generally, there was a good correspondence between the number of species sorted by taxonomists and the number of morphospecies sorted by parataxonomists. Despite higher taxonomic groups being present in most habitats, a large proportion of insect species was site- or habitat-specific. Anthropogenic modification of habitats did not result in a monotonic decline of abundance and diversity, as many herbivore pests and their associated predators and parasitoids invaded gardens, where plant productivity was kept artificially high year-round through watering and crop rotation. Because gardens were colonized mostly by invasive crop pests with little relation with the forest fauna, these results emphasize the concept of maintenance of ‘quality biodiversity’ and the value of considering other variables than species richness alone in conservation studies. Further, several lines of evidence indicated that savanna habitats at Gamba supported a species-poor arthropod fauna distinct from that in nearby habitats. It is therefore questionable whether in Africa insect assemblages of savanna represent a smaller subset of their neighboring forest fauna

Diversidade e métodos de amostragem de Hymenoptera na cultura da melancia no semiárido

Resumo: Os objetivos deste trabalho foram conhecer a fauna de Hymenoptera associada à cultura da melancia e avaliar a influência das armadilhas Pitfall, Moericke e McPhail na captura desses insetos, em ambiente semiárido no estado do Rio Grande do Norte. O levantamento foi realizado entre os meses de agosto e setembro de 2011, em área de produção comercial de melancia cv. Crimson Sweet. As coletas dos himenópteros foram realizadas, semanalmente, durante o ciclo da cultura. Para captura dos insetos, foram utilizados três tipos de armadilhas, Pitfall, Moericke e McPhail, na densidade de 20, 20 e 1 armadilha por hectare, respectivamente. As armadilhas foram instaladas sete dias após o plantio das sementes, e mantidas na área até a colheita dos frutos. Foram coletados um total de 3.123 himenópteros pertencentes a 10 superfamílias, distribuídas em 24 famílias. Formicidae foi a mais representativa, com abundância relativa total de 54,43%, seguida por Apidae com 17,96%. Foi observada também a presença de 18 famílias de himenópteros parasitoides (18,89%), com destaque para Platygastridae (6,60%), Encyrtidae (2,79%), Chalcididae (2,56%), Mymaridae (2,56%), Pompilidae (1,15%) e Trichogrammatidae (1,09%). Ressalta-se ainda a ocorrência das famílias de predadores Crabronidae (6,34%), Vespidae (2,24%) e Sphecidae (0,10%). Dentre as armadilhas, Moericke capturou a maior diversidade de Hymenoptera (24 famílias), seguida por Pitfall (11 famílias) e McPhail (sete famílias)