Biology subjects

Eggleton, P.

Publications and source records attributed to Eggleton, P..

3 recordsLinked to original sources

bioRxiv2021

Termites have developed wider thermal limits to cope with environmental conditions in savannas

The most diverse and abundant family of termites, the Termitidae, evolved in warm, wet African tropical forests. Since then, they have colonised grassy biomes such as savannas. These environments have more extreme temperatures than tropical forests, and greater temporal fluctuations (both annually and diurnally) that are challenging for soft-bodied ectotherms. We propose that that a likely mechanism that facilitated the expansion from forest to savanna was the widening of physiological limits of savanna termite species in order to cope with more extreme environmental conditions. We sampled termites directly from mound structures across an environmental gradient in Ghana, and recorded the thermal tolerance of individual termites, both critical thermal maximum (CTmax) and critical thermal minimum (CTmin). We estimated colony thermal tolerance by taking an average of each tested individual, and modelled these data against several environmental factors (canopy cover above the mound, rainfall and temperature). We found that savanna termite species had significantly higher CTmax values, and significantly lower CTmin values, than forest species. In addition, areas with high canopy cover were significantly associated with low CTmax values, and areas with higher average daily rainfall were significantly associated with higher CTmin values. Our results suggest that the widening of thermal tolerances has occurred in savanna termite species, probably in response to the more extreme temperatures found in those environments.

physiology↗

bioRxiv2020

Sharing the burden? Earthworms and woodlice show seasonal complementarity in peak abundances in soil in an oak-beech temperate woodland.

Complementarity between functional analogues can confer resistance and resilience on ecosystems in the face of environmental change. High biodiversity can lead to increased ecosystem functionality through complementary effects. Earthworms, woodlice and millipedes can have high densities in leaf litter and soils, but little is known about their seasonal patterns. The two groups play important roles in the breakdown and incorporation of organic matter into soils. Differences in peak abundance could affect the rates of litter break down and incorporation in different seasons. We sampled earthworms, woodlice and millipedes from leaf litter soil every month for ten years in a New Forest woodland. We used non-parametric regression to explore monthly and yearly variation in the abundance of decomposer organisms and soil temperature and moisture. Earthworms have a distinct seasonal peak in density different from woodlice and millipedes. Earthworm peak density is in the winter and spring and is correlated with greatest soil moisture. Woodlice (and millipede) have their peak density is in the summer and is correlated with the highest soil temperatures. This means that earthworms, woodlice and millipedes have complementary peaks in abundance. These two groups have similar functional roles in litter decomposition and these data imply ecological complementarity in this important ecological process. This effect is likely to be widespread in lowland woodland in the UK and Europe, with only extreme temperatures and low pH limiting the distribution. Increased summer drought as a result of climate change may lead to changes in the relative abundance of these three groups and in particular local extinctions of earthworms which will in turn affect litter decomposition.

ecology↗

bioRxiv2020

Darwin was right, in any given field, the spatial variability of earthworm communities in pastures isnt driven by measurable soil properties.

Abundance and distribution of earthworms in agricultural fields is frequently proposed as a measure of soil quality assuming that observed patterns of abundance are in response to improved or degraded environmental conditions. However, it is not clear that earthworm abundances can be directly related to their edaphic environment, as noted in Darwins final publication, perhaps limiting or restricting their value as indicators of ecological quality in any given field. We present results from a spatially explicit intensive survey of pastures within United Kingdom farms, looking for the main drivers of earthworm density at a range of scales. When describing spatial variability of earthworm abundance within any given field, the best predictor was earthworm abundance itself within 20 - 30 m of the sampling point; there were no consistent environmental correlates with earthworm numbers, suggesting that biological factors (e.g. colonisation rate, competition, predation, parasitism) drive or at least significantly modify earthworm distributions at this spatial level. However, at the national scale, earthworm abundance is well predicted by soil nitrate levels, density, temperature and moisture content, albeit not in a simple linear fashion. This suggests that although land can be managed at the farm scale to promote earthworm abundance and the resulting soil processes that deliver ecosystem services, within a field, earthworm distributions will remain patchy. The divergence in the interpretative value of earthworm abundance as an ecological indicator is a function of spatial scale, corresponding to species specific biological factors as well as a response to environmental pressures. Species abundance can effectively be used as ecological indicators, even if, at first, distributions seem random. However, care must be exercised, in the sampling design for the indicator species, if its abundance is to be used as a proxy for environmental quality at a particular scale (e.g. a management scale such as field scale).

ecology↗