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My niche
(2020)
Intraspecific trait variation is an important determinant of fundamental ecological interactions. Many of these interactions are mediated by behaviour. Therefore, interindividual differences in behaviour should contribute to individual niche specialization. Comparable with variation in morphological traits, behavioural differentiation between individuals should limit similarity among competitors and thus act as a mechanism maintaining within-species variation in ecological niches and facilitating species coexistence. Here, we aimed to test whether interindividual differences in boldness covary with spatial interactions within and between two ecologically similar, co-occurring rodent species (Myodes glareolus, Apodemus agrarius). In five subpopulations in northeast Germany, we quantified individual differences in boldness via repeated standardized tests and spatial interaction patterns via capture-mark- recapture (n = 126) and automated VHF telemetry (n = 36). We found that boldness varied with space use in both species. Individuals of the same population occupied different spatial niches, which resulted in non-random patterns of within- and between-species spatial interactions. Behavioural types mainly differed in the relative importance of intra- versus interspecific competition. Within-species variation along this competition gradient could contribute to maintaining individual niche specialization. Moreover, behavioural differentiation between individuals limits similarity among competitors, which might facilitate the coexistence of functionally equivalent species and, thus, affect community dynamics and local biodiversity.
Aboveground herbivory induces physiological responses, like the release of belowground chemical defense and storage of secondary metabolites, as well as physical responses in plants, like increased root biomass production. However, studies on effects of aboveground herbivory on root morphology are scarce and until now no study tested herbivory effects under natural conditions for a large set of plant species. Therefore, in a field experiment on plant-soil interactions, I investigated the effect of aboveground insect herbivory on root morphological traits of 20 grassland plant species. For 9 of the 20 species, all individuals showed shoot damage in the presence of insect herbivores, but no damage in insect herbivore exclusions. In these 9 species root biomass increased and root morphological traits changed under herbivory towards thinner roots with increased specific root surface. In contrast, the remaining species did not differ in the number of individuals damaged, root biomass nor morphological traits with herbivores present vs. absent. The fact that aboveground herbivory resulted in thinner roots with increased specific root surface area for all species in which the herbivore exclusion manipulation altered shoot damage might indicate that plants increase nutrient uptake in response to herbivory. However, more importantly, results provide empirical evidence that aboveground herbivory impacts root morphological traits of plants. As these traits are important for the occupation of soil space, uptake processes, decomposition and interactions with soil biota, results suggest that herbivory-induced changes in root morphology might be of importance for plant-soil feedbacks and plant-plant competition.
The competitive exclusion principle is one of the oldest ideas in ecology and states that without additional self-limitation two predators cannot coexist on a single prey. The search for mechanisms allowing coexistence despite this has identified niche differentiation between predators as crucial: without this, coexistence requires the predators to have exactly the same R* values, which is considered impossible. However, this reasoning misses a critical point: predators' R* values are not static properties, but affected by defensive traits of their prey, which in turn can adapt in response to changes in predator densities. Here I show that this feedback between defense and predator dynamics enables stable predator coexistence without ecological niche differentiation. Instead, the mechanism driving coexistence is that prey adaptation causes defense to converge to the value where both predators have equal R* values ("fitness equalization"). This result is highly general, independent of specific model details, and applies to both rapid defense evolution and inducible defenses. It demonstrates the importance of considering long-standing ecological questions from an eco-evolutionary viewpoint, and showcases how the effects of adaptation can cascade through communities, driving diversity on higher trophic levels. These insights offer an important new perspective on coexistence theory.