Almost all organisms on Earth exhibit ontogenetic niche shifts, which causes great phenotypic variation among individuals and is thus considered to critically mediate community structure and ...dynamics. In contrast, community ecology has traditionally assumed that species are composed of identical individuals with invariant traits and ignored the potentially important ecological roles of ontogenetic niche shifts. To bridge the gap, here I briefly review ecologically relevant examples which show that basic insights of species-based community theories can be revised by including the ontogenetic perspective. Specifically, I focus on the most representative animals in the study of ontogenetic niche shifts, i.e., fish, insects, and amphibians. Notably, their ontogenetic niche shifts create novel views of community structure: (1) ontogenetic diet shifts of predatory fish couple pelagic and benthic food webs in aquatic systems, (2) ontogenetic shifts in interaction types of pollinating insects couple herbivory and pollination networks in terrestrial systems, and (3) ontogenetic habitat shifts of amphibians and aquatic insects couple aquatic and terrestrial metacommunities at interface areas. Dynamic models of such stage-structured communities suggest that their ontogenetic niche shifts may affect the community resilience and disturbance responses. Exploring more complex systems (e.g., where many species undergo ontogenetic niche shifts several times or continuously) is a future direction, for which describing body size relationships between interacting organisms would be a promising approach. I conclude that both theoretical and empirical advances are needed to facilitate the ontogenetic perspective for better understanding mechanisms underlying biodiversity and ecosystem functioning which are increasingly threatened by anthropogenic disturbance.
Community ecology is traditionally species-based and assumes that species comprise identical individuals. However, intraspecific variation is ubiquitous in nature because of ontogenetic growth and ...critical in food-we dynamics. To understand individual interaction-mediated food webs, researchers have recently focused on body size as the most fundamental biological aspect and assessed a parameter called the predator–prey mass ratio (PPMR). Herein, I review the conceptual development of the PPMR and suggest four major concerns regarding its measurement: (1) PPMR should be measured at the individual level because species-averaged values distort actual feeding relationships, (2) individual-level PPMR data on gape-unconstrained predators (e.g., terrestrial carnivores) are limited because previous studies have targeted gape-limited fish predators, (3) predators’ prey size selectivity (preferred PPRM) is conceptually different from dietary prey size (realized PPMR) and should be distinguished by incorporating environmental prey abundance information, and (4) determinants of preferred PPMR, rather than those of realized PPMR, should be identified to describe size-dependent predation. Future studies are encouraged to explore not only predation but also other interaction types (e.g., competition, mutualism, and herbivory) at the individual level. However, this is not likely to occur while ecological communities are still considered to be interspecific interaction networks. To resolve this situation and more comprehensively understand biodiversity and ecosystem functioning, I suggest that community ecology requires a paradigm shift in the unit of interaction from species to individuals, similar to evolutionary biology, which revolutionized the unit of selection, because interactions occur between individuals.
Male and female pollinators often exhibit sex-specific preferences for visiting different flowers. Recent studies have shown that these preferences play an important role in shaping the network ...structure of pollination mutualism, but little is known about how they can mediate plant-plant interactions and coexistence of competing plants. The ecological consequences of sex-specific pollination can be complex. Suppose that a plant is favoured by female pollinators. They produce male pollinators, who may prefer visiting other competing plants and intensify the negative effects of inter-plant competition. Here, we analysed a simple two plant-one pollinator model with the sex structure of the pollinator. We observed that (i) sex-specific pollination can have complex consequences for inter-plant competition and coexistence (e.g. the occurrence of non-trivial alternative stable states in which one plant excludes or coexists with the other depending on the initial conditions), (ii) male and female pollinators have distinct ecological consequences because female pollinators have a demographic impact owing to reproduction, and (iii) plants are likely to coexist when male and female pollinators prefer different plants. These results suggest that sex-specific pollination is crucial for competition and coexistence of co-flowering plants. Future, pollination research should more explicitly consider the sex-specific behaviour of pollinating animals.
Climate change has significant impacts on phenology of various organisms in a species-specific manner. Facing this problem, the match/mismatch hypothesis that phenological (a) synchrony with resource ...availability strongly influences recruitment success of a consumer population has recently received much attention. In this article, we discuss extending the conventional pairwise concept and demonstrate a community module-based approach as an initial step for exploring community consequences of species-specific phenological shifts caused by climate change. Our multispecies match/mismatch perspective leads to the prediction that phenological (a) synchrony among interacting species critically affects not only population recruitment of species but also key dynamical features of ecological communities such as trophic cascades, competitive hierarchies, and species coexistence. Explicit identification and consideration of species relationships is therefore desirable for a better understanding of seasonal community dynamics and thus community consequences of climate change-induced phenological shifts.
It has been suggested that when juveniles and adults use different resources or habitats, alternative stable states (ASS) may exist in systems coupled by an ontogenetic niche shift. However, mainly ...the simplest system, i.e., the one-consumer-two-resource system, has been studied previously, and little is known about the development of ASS existing in more complex systems. Here, I theoretically investigated the development of ASS caused by an ontogenetic niche shift in the presence of multiple resource use. I considered three independent scenarios; (i) additional resources, (ii) multiple habitats, and (iii) interstage resource sharing. The model analyses illustrate that relative balance between the total resource availability in the juvenile and adult habitats is crucial for the development of ASS. This balance is determined by factors such as local habitat productivity, subsidy inputs, colonization area, and foraging mobility. Furthermore, it is also shown that interstage resource sharing generally suppresses ASS. These results suggest that the anthropogenic impacts of habitat modifications (e.g., fragmentation and destruction) or interaction modifications (e.g., changes in ontogeny and foraging behavior) propagate through space and may cause or prevent regime shifts in the regional community structure.
Reproductive interference is any interspecific sexual interaction that reduces the reproductive success of females through promiscuous reproductive activities of heterospecific individuals. This ...phenomenon is ubiquitous in nature in both plants and animals, and is frequently observed in biological invasions. However, its effects on interspecific competition remain incompletely understood despite growing concern. To study the interactive effects of resource competition and reproductive interference on species coexistence and exclusion, we analyzed a unified competition model including both processes in symmetric and asymmetric scenarios. The results of our model showed that resource competition and reproductive interference act synergistically to promote competitive exclusion. We also found that when the two processes are asymmetric, the species that is superior in reproductive interference can coexist with or even exclude the species that is superior in resource competition. Therefore, coexistence is possible via an unbalanced trade-off between resource use and reproduction. Our results suggest that integration of reproductive interference and resource competition will contribute to a better understanding of interspecific competition and to more effective biodiversity conservation against management of biological invasions.
In the ecological stoichiometry theory of population dynamics, ontogenetic changes in nutrient demand have been ignored. Here, I studied a stage-structured Daphnia-algae herbivore-autotroph model, in ...which the juveniles of the herbivore had a higher nutrient (phosphorous) demand for maturation than the adults for reproduction. The model predicted that while an increase in the juvenile nutrient demand (i.e., ontogenetic stoichiometric bottleneck) affects stage-specific performances in complex ways through nutrient dynamics and resource quality, in general it has stabilizing effects on the population dynamics.
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