Scale effects on the body size frequency distributions of African birds: patterns and potential mechanisms

Aim To describe and analyse the body size frequency distributions (BSFDs) of avian assemblages at several spatial scales in the Afrotropics. We also tested if the variation in median body size across assemblages at different spatial scales was related to environmental variables and whether purely stochastic processes could explain BSFDs. Location The Afrotropical biogeographic realm. Methods Avian body masses for 1960 species where analysed at continental, biome, ecoregion and local spatial scales with standardmetrics.Variation inmedian assemblage body size was modelled as a function of environmental and spatial explanatory variables to assess non-random assemblage structure. We tested if BSFDs of smaller spatial scale distributions are random subsets of the larger spatial scale assemblages in which they are embedded, and used three different null model randomizations to investigate the influence of stochastic processes on BSFDs. Results The African avifauna’s continental BSFD is unimodal and right-skewed. BSFDs generally become less skewed and less modal with decreasing spatial scale. The best-fit model explained 71% of median body size values at the ecoregion scale as a function of latitude, latitude2, longitude, species richness and species range size. BSFDs at smaller scales show non-random assembly from larger scale BSFDs distributions. Main conclusion African avifaunal BSFDs are quantitatively dissimilar to African mammal BSFDs, which are bimodal at all spatial scales.Much of the change in median body size with spatial scale can be captured by a range-weighted null model, suggesting that differential turnover between smaller- and larger-bodied species might explain the shift in the central tendency of the BSFD. At the local scale, energy may well contribute to structuring BSFDs, but this pattern is less pronounced at larger spatial scales

Conservation with Caveats

non

Land-use change promotes avian diversity at the expense of species with unique traits

Land-use change may alter both species diversity and species functional diversity patterns. To test the idea that species diversity and functional diversity changes respond in differing ways to land-use changes, we characterize the form of the change in bird assemblages and species functional traits along an intensifying gradient of land use in the savanna biome in a historically homogeneous vegetation type in Phalaborwa, South Africa. A section of this vegetation type has been untransformed, and the remainder is now mainly characterized by urban and subsistence agricultural areas. Using morphometric, foraging and breeding functional traits of birds, we estimate functional diversity changes. Bird species richness and abundance are generally higher in urban and subsistence agricultural land uses, as well as in the habitat matrix connecting these regions, than in the untransformed area, a pattern mainly driven through species replacement. Functionally unique species, particularly ground nesters of large body size, were, however, less abundant in more utilized land uses. For a previously homogenous vegetation type, declines in the seasonality of energy availability under land-use change have led to an increase in local avian diversity, promoting the turnover of species, but reduced the abundance of functionally unique species. Although there is no simple relationship between land-use and diversity change, land-use change may suit some species, but such change may also involve functional homogenization

Overgrazing and bush encroachment by Tarchonanthus camphoratus in a semi-arid savanna

Centre of Excellence for Invasion Biolog

Ensemble models predict Important Bird Areas in southern Africa will become less effective for conserving endemic birds under climate change

Aim: To examine climate change impacts on endemic birds, which are of global significance for conservation, on a continent with few such assessments. We specifically assess projected range changes in relation to the Important Bird Areas (IBAs) network and assess the possible consequences for conservation. Location: South Africa, Lesotho and Swaziland. Methods: The newly emerging ensemble modelling approach is used with 50 species, four climate change models for the period 2070-2100 and eight bioclimatic niche models in the statistical package BIOMOD. Model evaluation is done using the Receiver Operating Characteristic and the recently introduced True Skill Statistic. Future projections are made considering two extreme assumptions: species have full dispersal ability and species have no dispersal ability. A consensus forecast is identified using Principal Components Analysis. This forecast is interpreted in terms of the IBA network. An irreplaceability analysis is used to highlight priority IBAs for conservation attention in terms of climate change. Results: The majority of species (62%) are predicted to lose climatically suitable space. Five species lose at least 85% of their climatically suitable space. Many IBAs lose species (41%; 47 IBAs) and show high rates of species turnover of more than 50% (77%; 95 IBAs). Highly irreplaceable regions for endemic species become highly localised under climate change, meaning that the endemic species analysed here experience similar range contractions to maintain climate niches. Main conclusions: The South African IBAs network is likely to become less effective for conserving endemic birds under climate change. The irreplaceability analysis identified key refugia for endemic species under climate change, but many of these areas are not currently IBAs. In addition, many of these high priority areas that are IBAs fall outside of the current formal protected areas network.DST-NRF Centre of Excellence for Invasion Biology, the University of Pretoria, EU FP6 MACIS species targeted project (Minimisation of and Adaptation to Climate change: Impacts on biodiversity, contract No.: 044399) and EU FP6 ECOCHANGE integrated project (Challenges in assessing and forecasting biodiversity and ecosystem changes in Europe)

Microclimates mitigate against hot temperatures in dryland ecosystems: termite mounds as an example

Termite mounds have recently been shown to protect against drought by providing refuges for plants and foci for revegetation, but whether mounds modulate temperature remains untested. Organisms tend to experience climate at finer scales than those captured by models predicting how distributions alter with global change, so microclimates represent important “climate refuges.” Using data we collected from African savanna sites, generalized linear mixed-effects models and linear quantile regression analysis confirm for the first time that the woody species associated with large termite mounds establish microclimates that are significantly cooler than surrounding savannas, a cooling effect that is even greater at warmer extremes. As air temperatures approached 40°C, a cooling effect of up to 4°C occurred, representing a doubling from that observed at 34°C. African savannas encompass 10 million km2, and much of this harbors evenly dispersed termitaria. The temperature-modulating effect of mounds facilitates agricultural and conservation decision-making as global change begins to impact the integrity of both human well-being and ecological processes

Assessing local scale impacts of Opuntia stricta (Cactaceae) invasion on beetle and spider diversity in Kruger National Park, South Africa

There is a paucity of studies examining direct impacts of introduced alien species on biodiversity, a key need for motivating for alien species control in conservation areas. The introduced prickly pear (Opuntia stricta) has invaded some 35 000 ha of Kruger National Park. We investigated the effect of O. stricta on beetle and spider species assemblages in the Skukuza region of Kruger National Park. We used unbaited pitfall traps over a 12-month period in four treatments of varying O. stricta density. Species richness, species density and abundance of beetles and spiders were compared. A total of 72 beetle and 128 spider species were collected. Species richness and species density for beetles and spiders did not differ significantly across the four treatments. Assemblages for spiders did not differ across treatments but beetle assemblages were significantly different from uninvaded control sites. This study suggests that the current density of O. stricta does not significantly affect spider species richness, density or assemblages but that beetle assemblages are significantly affected.DST-NRF Centre for Invasion Biology and the University of Pretoria. Ditsong National Museum of Natural Histor