Functional Ecology

Numerous invasive and non‐invasive methods have been developed to characterize predator–prey interactions but two principal areas dominate ‘molecular’ research. These are reviewed under the headings of monoclonal antibodies and DNA‐based techniques.

Early ‘molecular’ studies of predator–prey food webs were dominated by the development of monoclonal antibodies. These methods continue to be used for mass‐screening of field‐collected arthropods for insect‐specific proteins.

The application of species‐specific primer design, polymerase chain reaction (PCR), restriction fragment length polymorphism analysis (RFLP), DNA cloning and sequencing, comparative sequence analysis (e.g. BLAST; basic local alignment search tool), high‐resolution gel electrophoresis, Temperature/denaturing gradient gel electrophoresis (TGGE/DGGE) and automated fragment analysis with fluorescent probes is reviewed. The development of molecular techniques for use in predator–prey studies is primarily limited by their cost and the development of new procedures and equipment that complement them.

We collected litters and associated soil samples from a secondary succession gradient ranging from herbaceous vegetation on recently abandoned ex‐arable fields to forest representing the end stage of succession. In a greenhouse, sterilized and unsterilized leaf litters were decomposed for 12 months in soils from early‐ to late‐successional stages according to a full‐factorial design. At the end, we examined fungal community composition on the decomposing litter.

Fungal communities on decomposed late‐successional litter in late‐successional soil differed from those in early‐ and mid‐successional stage litter and soil combinations. Soil source had the strongest impact on litter fungal composition when using sterilized litter, while the impact of litter type was strongest when using unsterilized litter. Overall, we observed HFA, as litter decomposition was accelerated in home soils. Increasing HFA did not relate to the dissimilarity in overall fungal composition, but there was increasing dissimilarity in the relative abundance of the most dominant fungal taxon between decomposing litter in home and away soils.

We conclude that early‐, mid‐ and late‐succession litter types did not exert strong selection effects on colonization by micro‐organisms from the soil species pool. Instead, fungal community composition on decomposing litter differed substantially between litter types for unsterilized litter, suggesting that the leaf microbiome, either directly or indirectly, is an important determinant of fungal community composition on decomposing leaves. HFA related most strongly to the abundance of the most dominant fungal taxa on the decomposing litter, suggesting that HFA may be attributed to some specific dominant fungi rather than to responses of the whole fungal community.

Plants and associated soil microbes have co‐evolved for millennia, generating adaptations to each other and to their local environment. This local co‐adaptation is likely generated by a suite of multidirectional exchanges of goods and services among plants, fungi and bacteria, and the constant changes in above‐ground–below‐ground interactions.

Resource limitation may be a driver of local adaptation among organisms involved in nutritional symbioses. The OA model states that when an essential resource is limited, natural selection will favour taxa that forage optimally by adjusting their biomass and energy allocation such that productivity is equally limited by all resources. Co‐adaptation will therefore respond to the local limiting resource conditions through taxa‐specific resource transfer interactions.

The OA model can help predict the outcomes of PSFs across a range of resource gradients and environmental changes such as increasing drought or atmospheric nitrogen deposition. Positive feedback is predicted in systems where resource exchange among plants and associated soil microbes can ameliorate resource limitation, or in systems where microbes provide another important service such as pathogen defence. Feedback strength is expected to diminish as resources become less limiting. Negative feedback is predicted when resources are in luxury supply and populations of opportunistic plant pathogens increase relative to commensal or mutualist microbes.

Future, field‐based studies that integrate naturally co‐occurring systems of plants, microbes and their local soil are needed to further test the hypothesis that resource availability is an effective predictor of the direction and magnitude of PSFs. A more mechanistic understanding of PSFs will help land managers and farmers to manipulate plant–microbial soil interactions to respond to environmental change and to effectively harness beneficial symbioses for plant nutrition and pathogen control.

A multivariate analysis of the four performance features revealed a clear difference between the physiological capacities of winners vs losers, with bite force being the most important predictor of the outcome of fights.

The finding that bite performance is linked to dominance fits in with the high sexual dimorphism in head size in this species, as head size is a predictor of bite force performance.

Winners of contests also tended to have larger total areas of blue patches on their sides, suggesting that these badges convey information on the social status of the males. However, since no correlation was found between bite force and badge size, the patches seem to contain information on a component of fighting capacity other than bite force.

We show that these different morphs do not differ significantly in morphological shape or bite force, a key aspect of fighting capacity. However, by contrast, the size of the belly patch is a significant predictor of maximum bite force, which is a predictor of dominance in other lizards.

We suggest that belly patch size and throat patch coloration are largely exclusive in that dominant individuals can exhibit small belly patches and low bite forces, whereas subordinate individuals can have large belly patches and high bite forces. Thus, embedded within the same male lizard display are divergent sexual structures that signal different traits, implying that the possession of multiple sexual signals within animals may be favoured by selection.

Here, differences in tolerance of elevated and subzero extreme temperatures were compared for field‐acclimatized and laboratory‐acclimated larvae and adults possessing three common PGI genotypes (PGI 1–1, 1–4 and 4–4). Three indices of thermal tolerance were measured – CT_max, LT₅₀and Hsp70 expression level.

Thermal tolerance depended on life stage, prior exposure to sublethal stress and PGI genotype. Larvae were generally less tolerant of thermal extremes than adults. For both adults and larvae, prior exposure to sublethal temperatures increased survival after exposure to subsequent stress. Survival after exposure to thermal extremes was consistently related to PGI genotype (1–1 > 1–4 > 4–4), as were expression levels of Hsp70 (1–1 > 1–4 > 4–4).

These results suggest that PGI genotypes differ in tolerance of thermal extremes routinely experienced by beetles in nature. A trade‐off between thermal tolerance and energy allocation may explain the persistence of the PGI polymorphism.