Spatial scale of observation affects α, β and γ diversity of cavity‐nesting bees and wasps across a tropical land‐use gradient

Abstract

Aim Anthropogenic changes in land use may have major consequences for global biodiversity. However, species diversity is determined by a suite of factors that may affect species differently at different spatial scales. We tested the combined effects of land use and spatial scale on a, b and c diversity in the tropics using experimental communities of cavity-nesting bees and wasps (Hymenoptera: Aculeata). We aimed to determine whether: (1) land-use intensity negatively affects species richness of cavity-nesting Hymenoptera, (2) b diversity, both within and between plots, is higher in more natural systems, (3) species richness of flowering herbs correlates positively with species richness of Hymenoptera within and across habitats, (4) richness of cavity-nesting Hymenoptera in highly modified habitats declines with increasing distance from natural or semi-natural habitats, (5) the effects of land use, herb diversity and forest distance on Hymenoptera a and b diversity vary at different spatial scales, and (6) bees and wasps respond to land use in a similar way.Location Manabi, south-west Ecuador.Methods We examined diversity (species richness) within 48 plots of five habitat types that comprised a gradient of decreasing agricultural intensity from rice and pasture to coffee agroforests, unmanaged abandoned agroforests and forest fragments, using standardized nesting resources for reproducing communities of cavity-nesting bees and wasps. Results(1) Land use significantly affected a diversity of trap-nesting bees and wasps at the subplot (per trap) scale, but not subplot b diversity or plot-scale species richness (c diversity). (2) Beta diversity was surprisingly higher between plots within a land-use type than between land-use types. (3) Species richness of bees and wasps increased with diversity of flowering herbs at the subplot (trap) scale only. (4) Forest distance correlated positively with bee species richness at the plot scale only. (5) Land use, herb diversity and forest distance each showed significant correlations with bee and wasp diversity at only one spatial scale. (6) Despite differences in life history, bees and wasps responded to land-use intensity in a similar way. Main conclusionsThe effects of land use on species richness were highly dependent on spatial scale. Subplot-scale analyses showed that rice and pasture contained the highest species diversity, whereas plot-scale analyses showed no significant difference in the diversity of different land-use types. We emphasize caution in the estimation of biodiversity at only one spatial scale, and highlight the surprisingly large contribution of managed land to the regional biodiversity of these species.

Diversity of cavity-nesting bees (Hymenoptera: Apoidea) within apple orchards and wild habitats in the Annapolis Valley, Nova Scotia, Canada

“…4); the unrealized fecundity in the agricultural (and past agricultural) sites may reflect shortages of food plants in these habitats (Williams and Kremen 2007), as weed management occurred routinely, at least within the commercial orchards. Therefore, it seems likely that trap nest surveys alone (e.g., Klein et al 2002;Steffan-Dewenter 2002;Tylianakis et al 2006) provide only a partial picture of potential species richness and abundance of cavity-nesting bees when the results are compared across diverse landscapes.…”

The invasive Yellow Crazy Ant and the decline of forest ant diversity in Indonesian cacao agroforests

“…However, the identity of the species changed considerably as almost half of the forest ant species were not found in agroforests and vice versa. High species turnover between tropical habitats is common, and can result from habitat heterogeneity at the landscape scale (e.g., Tylianakis et al 2006;Bos et al 2007b). In our comparison, most habitat differences at the landscape scale resulted from differences between natural forests and cacao-dominated agroforests, and the most common species that did not occur in both habitat types was the Yellow Crazy Ant Anoplolepis gracilipes (18% of all ants collected from cacao trees).…”

“…Agroforests can indeed support high levels of species richness, even resembling that of undisturbed tropical forests (Room 1971;Majer et al 1994;Perfecto et al 1997;Schulze et al 2004;Tylianakis et al 2006). However, the species richness supported depends on the complexity of the agroforest habitat (Armbrecht et al 2004;SteffanDewenter et al 2007), and recent intensification of existing tropical agroforests has caused rapid declines in associated biodiversity (Perfecto et al 1997;Schulze et al 2004;Bos et al 2007a).…”

How Should Beta-Diversity Inform Biodiversity Conservation?

“…Conversely, when land use intensification leads to high abundances and local richness of a particular group (e.g. hoverflies in Europe [44], bees and wasps in Ecuador [52]), beta-diversity is likely to decline. Although there are some clear generalities, many changes appear idiosyncratic.…”