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Insect Species Richness (insect + species_richness)
Selected AbstractsScale dependence of effective specialization: its analysis and implications for estimates of global insect species richnessDIVERSITY AND DISTRIBUTIONS, Issue 1 2007Jon C. Gering ABSTRACT Estimates of global insect species richness are sometimes based on effective specialization, a calculation used to estimate the number of insect species that is restricted to a particular tree species. Yet it is not clear how effective specialization is influenced by spatial scale or characteristics of the insect community itself (e.g. species richness). We investigated scale dependence and community predictors of effective specialization using 15,907 beetles (583 species) collected by insecticide fogging from the crowns of 96 trees (including 32 Quercus trees) located in Ohio and Indiana. Trees were distributed across 24 forest stands (,1 ha) nested within six sites (,10,100 km2) and two ecoregions (> 1000 km2). Using paired-sample randomization tests, we found that effective specialization (fk) exhibited negative scale-dependence in early (May,June 2000) and late (August,September 2000) sampling periods. Our average effective specialization (F) values , those that are comparable to Erwin's (1982) estimates , ranged from 19% to 97%, and increased as spatial scale decreased. We also found that beetle species richness and the number of shared beetle species across host trees were significant and consistent negative predictors of F. This shows that increases in spatial scale, species richness, and the number of trees (and/or tree species) all coincide with decreases in effective specialization. Collectively, our results indicate that estimates of global insect species richness based on effective specialization at a single spatial scale are overestimating the magnitude of global insect species richness. We propose that scale dependence should be promoted to a central concept in the research program on global estimates of species richness. [source] Four ways towards tropical herbivore megadiversityECOLOGY LETTERS, Issue 4 2008Thomas M. Lewinsohn Abstract Most multicellular species alive are tropical arthropods associated with plants. Hence, the host-specificity of these species, and their diversity at different scales, are keys to understanding the assembly structure of global biodiversity. We present a comprehensive scheme in which tropical herbivore megadiversity can be partitioned into the following components: (A) more host plant species per se, (B) more arthropod species per plant species, (C) higher host specificity of herbivores, or (D) higher species turnover (beta diversity) in the tropics than in the temperate zone. We scrutinize recent studies addressing each component and identify methodological differences among them. We find substantial support for the importance of component A, more tropical host species. A meta-analysis of published results reveals intermediate to high correlations between plant and herbivore diversity, accounting for up to 60% of the variation in insect species richness. Support for other factors is mixed, with studies too scarce and approaches too uneven to allow for quantitative summaries. More research on individual components is unlikely to resolve their relative contribution to overall herbivore diversity. Instead, we call for the adoption of more coherent methods that avoid pitfalls for larger-scale comparisons, for studies assessing different components together rather than singly, and for studies that investigate herbivore beta-diversity (component D) in a more comprehensive perspective. [source] Herbivores, but not other insects, are scarce on alien plantsAUSTRAL ECOLOGY, Issue 5 2008ERBAN PROCHE Abstract Understanding how the landscape-scale replacement of indigenous plants with alien plants influences ecosystem structure and functioning is critical in a world characterized by increasing biotic homogenization. An important step in this process is to assess the impact on invertebrate communities. Here we analyse insect species richness and abundance in sweep collections from indigenous and alien (Australasian) woody plant species in South Africa's Western Cape. We use phylogenetically relevant comparisons and compare one indigenous with three Australasian alien trees within each of Fabaceae: Mimosoideae, Myrtaceae, and Proteaceae: Grevilleoideae. Although some of the alien species analysed had remarkably high abundances of herbivores, even when intentionally introduced biological control agents are discounted, overall, herbivorous insect assemblages from alien plants were slightly less abundant and less diverse compared with those from indigenous plants , in accordance with predictions from the enemy release hypothesis. However, there were no clear differences in other insect feeding guilds. We conclude that insect assemblages from alien plants are generally quite diverse, and significant differences between these and assemblages from indigenous plants are only evident for herbivorous insects. [source] Diversity of insect-induced galls along a temperature, rainfall gradient in the tropical savannah region of the Northern Territory, AustraliaAUSTRAL ECOLOGY, Issue 4 2000K. R. Blanche Abstract Evidence regarding the effect of temperature and rainfall on gall-inducing insects is contradictory: some studies indicate that species richness of gall-inducing insects increases as environments become hotter and drier, while others suggest that these factors have no effect. The role of plant species richness in determining species richness of gall-inducing insects is also controversial. These apparent inconsistencies may prove to be due to the influence of soil fertility and the uneven distribution of gall-inducing insect species among plant taxa. The current study tested hypotheses about determinants of gall-inducing insect species richness in a way different to previous studies. The number of gall-inducing insect species, and the proportion of species with completely enclosed galls (more likely to give protection against heat stress and desiccation), were measured in replicate plots at five locations along a 500-km N-S transect in the seasonal tropics of the Northern Territory, Australia. There is a strong temperature,rainfall gradient along this transect during the wet season. Plant species lists had already been compiled for each collection plot. All plots were at low elevation in eucalypt savannah growing on infertile soils. There was no evidence to suggest that hot, dry environments in Australia have more gall-inducing insect species than cooler, wetter environments, or that degree of enclosure of galls is related to protecting insects from heat stress and desiccation. The variable number of gall-inducing insect species on galled plant species meant that plant species richness did not influence gall species richness. Confirmation is still required that low soil fertility does not mask temperature,rainfall effects and that galls in the study region are occupied predominantly in the wet season, when the temperature,rainfall gradient is most marked. [source] Effects of Hygrothermal Stress, Plant Richness, and Architecture on Mining Insect DiversityBIOTROPICA, Issue 2 2004G. Wilson Fernandes ABSTRACT We investigated the distribution patterns of leaf mining insects along an elevational gradient in cerrado vegetation of southeastern Brazil. We tested four hypotheses related to the distribution of mining insects: (1) the "altitudinal gradient hypothesis," which predicts that mining insect species richness will decrease with altitude or elevation; (2) the "habitat-mediated richness hypothesis," which predicts that mining insect species richness will be higher in mesic habitats than in xeric habitats; (3) the "plant species richness hypothesis," which predicts that mining insect species richness will be positively correlated with plant species richness; and (4) the "plant architecture hypothesis," which predicts a positive correlation between mining insect species richness and plant structural complexity. A total of 33,000 herbs, 3520 shrubs, and 1760 trees were sampled at 44 sites across an elevational gradient of 700 m. Mining insect species richness and plant species richness showed a negative correlation with elevation in xeric habitats, while in mesic habitats mining insect species and plant species richness did not show any statistically significant relationship with elevation. The differential distribution of mining insect species between xeric and mesic habitats supported the habitat-mediated richness hypothesis, which states that miners would be more speciose in mesic, more favorable habitats. Mining species richness also increased with increasing plant structural complexity. The results suggest that the mining habit may not represent a strong adaptive strategy in protecting mining insects against desiccation. RESUMEN Nós investigamos os padrões de distribuição de insetos minadores ao longo de um gradiente altiudinal no cerrado, no sudeste do Brasil. Testamos quatro hipóteses relacionadas a distribuição de insetos minadores: (1) a "hipótese do gradiente altitudinal" que prediz que a riqueza de espécies de minadores aumenta com o decréscimo da altitude; (2) a "hipótese da riqueza mediada pelo habitat" que prediz que a riqueza de espécies de minadores deve ser maior em habitats mesicos que em habitats xéricos; (3) a "hipótese da riqueza de espécies de plantas" que prediz que a riqueza de espécies de minas deve ser positivamente correlacionada com a riqueza de espécies de plantas; e (4) a "hipótese da arquitetura da planta" que prediz uma correlação positiva entre riqueza de espécies de minas e complexidade estrutural das plantas. Foram amostradas 33,000 ervas, 3520 arbustos, e 1760 árvores, em 44 sitios ao longo de um gradiente de 700 m: A riqueza de espécies de minadores e de plantas apresentou uma correlação negativa com a altitude em habitats xéricos. Entretanto, em habitats mésicos as espécies de minadores e a riqueza de espécies de plantas não apresentaram nenhuma relação estatisticamente significativa com a altitude. A distribuição diferencial de espécies de minadores entre habitats xéricos e mésicos corroborou a hipótese da riqueza mediada pelo habitat, segundo a qual a riqueza de minas deve ser maior em habitats mésicos, que são mais favoráveis. A riqueza de espécies de minadores aumentou corn o aumento da complexidade estrutural da planta. Estes resultados sugerem que o hábito minador não deve representar uma forte estratégia adaptativa para fornecer aos minadores proteção contra dessecação. [source] | ||||||||||