When populations face different environmental conditions, both local adaptation and phenotypic plasticity may cause interpopulation divergence of behavioral or phenotypic properties on which mate choice is based. If sustained, this may result in genetic differentiation even in the presence of extant gene flow. Condition dependence of mate choice is one of the main mechanisms explaining these environmental effects. We tested whether experimental food stress affects mate choice in male and female Pirata piraticus spiders from one heavily polluted and one unpolluted reference population. Compared with control females, food-stressed females from the reference population showed a decreased probability of copulation and preferred smaller mates. Females from the polluted population, in contrast, did not show a significant response to food stress and showed size-assortative mating, most strongly under food stress. We explain these results in 2 complementary ways. First, spiders from populations that are not adapted to cope with stress may be less willing to mate when eggs are not fully matured. Second, food-deprived females may show a larger responsiveness toward smaller males because the latter resemble prey more and hungry females tend to attack moving objects more often. Results from this study support the prediction that variation in body condition, driven by local ecological factors, may affect mating behavior and may ultimately lead to population divergence in important life-history traits such as body size.
Located in
Library
/
RBINS Staff Publications
P1. Positive effects of species diversity on ecosystem functioning have often been demonstrated in 'macrobial' communities. This relation and the responsible mechanisms are far less clear for microbial communities. Most experimental studies on microorganisms have used randomly assembled communities that do not resemble natural communities. It is therefore difficult to predict the consequences of realistic, non-random diversity loss. 2. In this study, we used naturally co-occurring diatom species from intertidal mudflats to assemble communities with realistically decreasing diversity and analysed the effect of non-random species loss on biomass production. 3. Our results demonstrate a highly positive biodiversity effect on production, with mixtures outperforming the most productive component species in more than half of the combinations. These strong positive diversity effects could largely be attributed to positive complementarity effects (including both niche complementarity and facilitation), despite the occurrence of negative selection effects which partly counteracted the positive complementarity effects at higher diversities. 4. Facilitative interactions were, at least in part, responsible for the higher biomass production. For one of the species, Cylindrotheca closterium, we show its ability to significantly increase its biomass production in response to substances leaked into the culture medium by other diatom species. In these conditions, the species drastically reduced its pigment concentration, which is typical for mixotrophic growth. 5. Synthesis. We show that both species richness and identity have strong effects on the biomass production of benthic diatom biofilms and that transgressive overyielding is common in these communities. In addition, we show mechanistic evidence for facilitation which is partly responsible for enhanced production. Understanding the mechanisms by which diversity enhances the performance of ecosystems is crucial for predicting the consequences of species loss for ecosystem functioning.
Located in
Library
/
RBINS Staff Publications
Habitat fragmentation may influence the genetic structure of populations, especially of species with low mobility. So far, these effects have been mainly studied by surveying neutral markers, and much less by looking at ecologically relevant characters. Therefore, we aimed to explore eventual patterns of covariation between population structuring in neutral markers and variation in shell morphometrics in the forest-associated snail Discus rotundatus in relation to habitat fragment characteristics. To this end, we screened shell morphometric variability and sequence variation in a fragment of the mitochondrial 16S rDNA gene in D. rotundatus from the fragmented landscape of the Lower Rhine Embayment, Germany. The 16S rDNA of D. rotundatus was highly variable, with a total of 118 haplotypes (384 individuals) forming four clades and one unresolved group. There was a geographic pattern in the distribution of the clades with the river Rhine apparently separating two groups. Yet, at the geographic scale considered, there was no obvious effect of fragmentation on shell morphometrics and 16S rDNA variation because G(ST) often was as high within, as between forests. Instead, the age of the habitat and (re-)afforestation events appeared to affect shell shape and 16S rDNA in terms of the number of clades per site. The ecologically relevant characters thus supported the presumably neutral mitochondrial DNA markers by indicating that populations of not strictly stenecious species may be (relatively) stable in fragments. However, afforestation after large clearcuts and habitat gain after the amendment of deforestation are accompanied by several, seemingly persistent peculiarities, such as altered genetic composition and shell characters (e.g. aperture size). (C) 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 839-850.
Located in
Library
/
RBINS Staff Publications