Individual Niche Specialization Research Articles

The spatiotemporal context of individual specialization in resource use and environmental associations.

1. Individual niche specialization is widespread in natural populations and has key implications for higher levels of biological organization. This phenomenon, however, has been primarily quantified in resource niche axes, overlooking individual variation in environmental associations (i.e. abiotic conditions organisms experience). 2. Here, we explore what we can learn from a multidimensional perspective of individual niche specialization that integrates resource use and environmental associations into a common framework. 3. By combining predictions from theory and simple simulations, we illustrate how (i) multidimensional intraspecific niche variation and (ii) the spatiotemporal context of interactions between conspecifics scale up to shape emergent patterns of the population niche. 4. Contemplating individual specialization as a multidimensional, unifying concept across biotic and abiotic niche axes is a fundamental step towards bringing this concept closer to the n-dimensional niche envisioned by Hutchinson.

Individual diet specialization in the spider Tidarren haemorrhoidale (Bertkau, 1880) (Theridiidae)

AbstractIndividual specialization (IS) in resource use is common within populations of several animal species because some individuals can be more efficient than others in obtaining specific food items. Spiders are usually classified as euryphagous predators, but the broad diet of populations may result from many individuals specializing in capturing different types of prey. Empirical evidence supporting this pattern, however, is still scarce. In this study, we hypothesized that (1) the diet of individuals of Tidarren haemorrhoidale is more restricted than the population's diet and (2) individual diet restrictions are not determined by the spatial distribution of prey types. We collected the prey remains of 74 webs of females in a conservation area of the Atlantic Forest. Our results indicated that T. haemorrhoidale could be considered a euryphagous predator because its diet comprised Opiliones, Diplopoda, and eight orders of insects. However, spiders exhibited moderate and high degrees of IS for prey size and taxa, respectively. There was no modularity for both prey attributes in the food web, but there was a medium nestedness. Most individuals captured ants, but additional prey taxa were of different orders. There was no correlation between the dissimilarity of prey taxa and the distances between the webs, suggesting that IS did not occur based on the spatial distribution of their potential prey. The diversity of prey defensive strategies may induce spiders to perform specific behavioral routines after prey interception. If this occurs, cognitive constraints may limit their ability to use different capture routines efficiently. Our study supports the predictions of individual niche specialization theory for a euryphagous spider species and highlights the potential of spiders as a study model to investigate the underlying mechanisms.

Diet experiences early in life mold individual foraging niches and personalities of omnivorous predatory mites

The theory of individual niche specialization posits that members of local groups should diversify in their realized individual diet niches to alleviate inter-individual food competition and ensuing conflicts (Bolnick et al. 2003). Here we tested the hypothesis that early life experiences co-shape individual specialization in diet niches and animal personality expression in the omnivorous plant-inhabiting predatory mite Amblyseius swirskii.

The landscape of fear has individual layers: an experimental test of among‐individual differences in perceived predation risk during foraging

Perceived predation risk varies in space and time creating a landscape of fear. This key feature of an animal's environment is classically studied as a species‐specific property. However, individuals differ in how they solve the tradeoff between safety and reward and may, hence, differ consistently and predictively in perceived predation risk across landscapes. To test this hypothesis, we quantified among‐individual differences in boldness and activity and exposed behaviourally phenotyped male bank voles Myodes glareolus individually to two different experimental landscapes of risks in large outdoor enclosures and provided resources as discrete food patches. We manipulated perceived predation risk via vegetation height between 2 and > 30 cm and quantified patch use indirectly via RFID‐logging and giving‐up densities. We statistically disentangled among‐individual differences in microhabitat use from spatially varying perceived risk, i.e. landscape of fear. We found that individuals varied in mean vegetation height of their foraging microhabitats and that this microhabitat selection matched the intrinsic individual differences in perceived risk. As predicted by the patch use model, all individual's perceived higher risks when foraging in lower vegetation. However, individuals differed in their reaction norm slopes of perceived risk to vegetation height, and these differences in slopes were consistent across two different landscapes of risks and resources. We interpret these results as evidence for individual landscapes of fear, which could be predicted by among‐individual differences in activity and boldness. Since perceived predation risk affects when and where to forage, among‐individual differences in fear responses could act as a mode of intraspecific niche complementarity (i.e. individual niche specialization), help explain behavioural type by environment correlations, and will likely have cascading indirect effects on lower trophic levels.

Resource preferences and the emergence of individual niche specialization within populations

AbstractGrowing evidence that individuals of many generalist animals behave as resource specialists have attracted substantial research interest for its ecological and evolutionary implications. Variation in resource preferences is considered to be critical for developing a general theory of individual specialization. However, it remains to be shown whether diverging preferences can arise among individuals sharing a similar environment, and whether these preferences are sufficiently stable over time to be ecologically relevant. We addressed these issues by means of common garden experiments in feral pigeons (Columba livia), a species known to exhibit among-individual resource specialization in the wild. Food-choice experiments on wild-caught pigeons and their captive-bred cross-fostered descendants showed that short-term variation in food preferences can easily arise within a population, and that this variation may represent a substantial fraction of the population foraging niche. However, the experiments also showed that, rather than being limited by genetic or vertical cultural inheritance, food preferences exhibited high plasticity and tended to converge in the long-term. Although our results challenge the notion that variation in food preferences is a major driver of resource specialization, early differences in preferences could pave the way to specializations when combined with neophobic responses and/or positive feedbacks that reinforce niche conservation.

Regulation of fatty acid composition related to ontogenetic changes and niche differentiation of a common aquatic consumer

Fatty acids (FAs) are key nutrients for fitness which take part in multiple physiological processes over the ontogeny of organisms. Yet, we lack evidence on how FA nutrition mediates life-history trade-offs and ontogenetic niche shifts in natural populations. In a field study, we analyzed ontogenetic changes in the FAs of Eurasian perch (Perca fluviatilis L.), a widespread fish that goes through ontogenetic niche shifts and can have high individual niche specialization. Diet explained most of the variation in the FA composition of perch dorsal muscle over early ontogeny (28%), while the total length explained 23%, suggesting that perch significantly regulated FA composition over early ontogeny. Condition explained 1% of the remaining variation. 18:3n-3 (ALA) and 18:4n-3 (SDA) indicated planktivory; 18:1n-7, benthivory; and 22:6n-3 (DHA), piscivory in perch diet. Conversely, perch regulated long-chained polyunsaturated fatty acids (PUFAs), such as 20:5n-3 (EPA), 20:4n-6 (ARA) and 22:6n-3 (DHA) over ontogeny, emphasizing the role of such FAs in early growth and sexual maturation. Adult perch increasingly retained 16:1n-7 and 18:1n-9 suggesting higher energy storage in older perch. Furthermore, differences in DHA availability in diet correlated with intra-cohort differences in perch growth, potentially hindering the overall use of benthic resources and promoting earlier shifts to piscivory in littoral habitats. Overall, this study indicates that in addition to diet, internal regulation may be more important for FA composition than previously thought. Differences between FA needs and FA availability may lead to life-history trade-offs that affect the ecology of consumers, including their niche.

My niche: individual spatial niche specialization affects within- and between-species interactions.

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.

Individuals in space: personality-dependent space use, movement and microhabitat use facilitate individual spatial niche specialization

Personality-dependent space use and movement might be crucially influencing ecological interactions, giving way to individual niche specialization. This new approach challenges classical niche theory with potentially great ecological consequences, but so far has only scarce empirical support. Here, we investigated if and how consistent inter-individual differences in behavior predict space use and movement patterns in free-ranging bank voles (Myodes glareolus) and thereby contribute to individual niche specialization. Individuals were captured and marked from three different subpopulations in North-East Germany. Inter-individual differences in boldness and exploration were quantified via repeated standardized tests directly in the field after capture. Subsequently, space use and movement patterns of a representative sample of the behavioral variation (n = 21 individuals) were monitored via automated VHF telemetry for a period of four days, yielding on average 384 locations per individual. Bolder individuals occupied larger home ranges and core areas (estimated via kernel density analyses), moved longer distances, spatially overlapped with fewer conspecifics and preferred different microhabitats based on vegetation cover compared to shyer individuals. We found evidence for personality-dependent space use, movement, and occupation of individual spatial niches in bank voles. Thus, besides dietary niche specialization also spatial dimensions of ecological niches vary among individuals within populations, which may have important consequences for ecological interactions within- and between species.

Drivers of individual niche variation in coexisting species.

Although neglected by classic niche theory, individual variation is now recognized as a prevalent phenomenon in nature with evolutionary and ecological relevance. Recent theory suggests that differences in individual variation across competitors can affect species coexistence and community patterns. However, the degree of individual variation is flexible across wild populations and we still know little about the ecological drivers of this variation across populations of single species and, especially, across coexisting species. Here, we aimed to (a) elucidate the major drivers of individual niche variation in natural communities and (b) to determine how consistent this variation is across coexisting species and communities. We analysed natural patterns of individual-level niche variation in four species of coexisting generalist frogs across a wide range of tropical communities. Specifically, we used gut contents and stable isotopes (δ13 C and δ15 N) from frog species and their prey to quantify individual niche specialization. Then, we combined data on local community structure, availability of prey, phylogenetic relationships and predator-prey size models to test how this variation is related to four ecological factors which are predicted to be key drivers of individual specialization: intraspecific competition, interspecific competition, ecological opportunity (i.e., diversity of resources) and predation. We found that the degree of individual trophic specialization varied by up to ninefold across populations within the same species. This sizable variation in trophic specialization across populations was at least partially explained by gradients of density of competitors (both conspecifics and heterospecifics) and intraguild predation. However, the specific relationships between individual specialization and these ecological gradients were strongly species-specific. As consequences, the identity of the species with more individual variation changed among sites and there was typically no spatial correlation in the degree of individual specialization across coexisting species. Our results show that individual niche specialization within and across species can be strongly context-dependent and that hierarchies of individual variation among coexisting species are not necessarily consistent across communities. Recent theory suggests that this pattern could lead to concurrent changes in competitive interactions across sites and thereby could play a key role in species coexistence at the landscape level. Our results suggest that individual variation across and within coexisting species has the potential to affect not only species coexistence at local communities, but also regional diversity patterns.

The dimensionality of individual niche variation.

The inherently multidimensional nature of the niche has not yet been integrated into the investigation of individual niche specialization within populations. We propose a framework for modeling the between- and within-individual components of the population niche as a set of variance-covariance matrices, which can be visualized with ellipses or ellipsoids. These niche components can be inferred using multiple response mixed models, and can incorporate diverse types of data, including diet composition, stable isotopes, spatial location, and other continuous measures of niche dimensions. We outline how considering both individual and population niches in multiple dimensions may enhance our understanding of key concepts in ecology and evolution. Considering multiple dimensions as well as the within-individual component of variation can lead to more meaningful measures of niche overlap between species. The impact of a population on its food web or ecosystem can depend on the degree of individual variation (via Jensen's inequality), and we suggest how the dimensionality of individual specialization could amplify this effect. Finally, we draw from concepts in quantitative genetics and the study of animal personalities to propose new hypotheses about the ecological and evolutionary basis of niche shifts in multiple dimensions. We illustrate key ideas using empirical data from sea otters, wetland frogs, and threespine stickleback, and discuss outstanding questions about the consequences of multidimensional niche variation. Setting variation among individuals in an explicitly multivariate framework has the potential to transform our understanding of a range of ecological and evolutionary processes.

Community structure affects trophic ontogeny in a predatory fish.

While most studies have focused on the timing and nature of ontogenetic niche shifts, information is scarce about the effects of community structure on trophic ontogeny of top predators. We investigated how community structure affects ontogenetic niche shifts (i.e., relationships between body length, trophic position, and individual dietary specialization) of a predatory fish, brown trout (Salmo trutta). We used stable isotope and stomach content analyses to test how functional characteristics of lake fish community compositions (competition and prey availability) modulate niche shifts in terms of (i) piscivorous behavior, (ii) trophic position, and (iii) individual dietary specialization. Northern Scandinavian freshwater fish communities were used as a study system, including nine subarctic lakes with contrasting fish community configurations: (i) trout‐only systems, (ii) two‐species systems (brown trout and Arctic charr [Salvelinus alpinus] coexisting), and (iii) three‐species systems (brown trout, Arctic charr, and three‐spined sticklebacks [Gasterosteus aculeatus] coexisting). We expected that the presence of profitable small prey (stickleback) and mixed competitor–prey fish species (charr) supports early piscivory and high individual dietary specialization among trout in multispecies communities, whereas minor ontogenetic shifts were expected in trout‐only systems. From logistic regression models, the presence of a suitable prey fish species (stickleback) emerged as the principal variable determining the size at ontogenetic niche shifts. Generalized additive mixed models indicated that fish community structure shaped ontogenetic niche shifts in trout, with the strongest positive relationships between body length, trophic position, and individual dietary specialization being observed in three‐species communities. Our findings revealed that the presence of a small‐sized prey fish species (stickleback) rather than a mixed competitor–prey fish species (charr) was an important factor affecting the ontogenetic niche‐shift processes of trout. The study demonstrates that community structure may modulate the ontogenetic diet trajectories of and individual niche specialization within a top predator.

Factors affecting individual foraging specialization and temporal diet stability across the range of a large "generalist" apex predator.

Individual niche specialization (INS) is increasingly recognized as an important component of ecological and evolutionary dynamics. However, most studies that have investigated INS have focused on the effects of niche width and inter- and intraspecific competition on INS in small-bodied species for short time periods, with less attention paid to INS in large-bodied reptilian predators and the effects of available prey types on INS. We investigated the prevalence, causes, and consequences of INS in foraging behaviors across different populations of American alligators (Alligator mississippiensis), the dominant aquatic apex predator across the southeast US, using stomach contents and stable isotopes. Gut contents revealed that, over the short term, although alligator populations occupied wide ranges of the INS spectrum, general patterns were apparent. Alligator populations inhabiting lakes exhibited lower INS than coastal populations, likely driven by variation in habitat type and available prey types. Stable isotopes revealed that over longer time spans alligators exhibited remarkably consistent use of variable mixtures of carbon pools (e.g., marine and freshwater food webs). We conclude that INS in large-bodied reptilian predator populations is likely affected by variation in available prey types and habitat heterogeneity, and that INS should be incorporated into management strategies to efficiently meet intended goals. Also, ecological models, which typically do not consider behavioral variability, should include INS to increase model realism and applicability.

Does prey mobility affect niche width and individual specialization in hunting wasps? A network‐based analysis

Niche width and inter‐individual diet variation in predator populations are known to be affected by intrinsic factors such as body size, age, cognitive constraints, and by intra‐ and interspecific competition. By contrast, how variation in prey biological traits may affect niche width and partitioning is still a poorly explored topic. One of these candidate traits is prey mobility, which can affect the predators’ niche because acting on the rate of encounter and, assuming mobility as a proxy for escape capability, on the success of predator attacks. Here we analysed 20 wasp populations and their prey as individual‐based food‐webs to test if prey mobility may explain niche width (here defined by the Shannon entropy‐based index ) and patterns of inter‐individual diet variation (here defined by the interaction‐exclusiveness index H2′ and the interaction evenness index E2). Niche width was very variable among populations and overall network specialization (H2′) was always higher than the expected by null models. In case of high‐speed flying prey (e.g. flies, bees), wasps showed wider niches () and lower specialization (H2′) than in case of non‐flying or slow‐flying prey (e.g. spiders, beetles). Evenness (E2), on the other side, did not vary with prey mobility. Altogether, these results suggest that highly elusive prey may lead to wider predators’ niche but somehow limit their individual niche specialization.

Stable isotope series from elephant ivory reveal lifetime histories of a true dietary generalist

Longitudinal studies have revealed how variation in resource use within consumer populations can impact their dynamics and functional significance in communities. Here, we investigate multi-decadal diet variations within individuals of a keystone megaherbivore species, the African elephant (Loxodonta africana), using serial stable isotope analysis of tusks from the Kruger National Park, South Africa. These records, representing the longest continuous diet histories documented for any extant species, reveal extensive seasonal and annual variations in isotopic--and hence dietary--niches of individuals, but little variation between them. Lack of niche distinction across individuals contrasts several recent studies, which found relatively high levels of individual niche specialization in various taxa. Our result is consistent with theory that individual mammal herbivores are nutritionally constrained to maintain broad diet niches. Individual diet specialization would also be a costly strategy for large-bodied taxa foraging over wide areas in spatio-temporally heterogeneous environments. High levels of within-individual diet variability occurred within and across seasons, and persisted despite an overall increase in inferred C(4) grass consumption through the twentieth century. We suggest that switching between C(3) browsing and C(4) grazing over extended time scales facilitates elephant survival through environmental change, and could even allow recovery of overused resources.

Trophic Niche Variation and Individual Specialization inHypsiboas pulchellus(Duméril and Bibron, 1841) (Anura, Hylidae) from Uruguay

6 Corresponding author. ABSTRACT. Intrapopulation variation includes age and sexual variation, but also individual niche specialization. Individual specialization has important effects on dynamics at population or community levels. Environmental variation and intraspecific interactions are factors that can promote or enhance this kind of variation. Despite its relevance, knowledge about individual specialization in amphibians is still scarce, especially in species from temperate regions. In this study we analyzed the intrapopulational variation of the trophic niche in Hypsiboas pulchellus from a population in southern Uruguay. Particularly, we analyzed ontogenetic and sexual variation and individual specialization of the diet. We found ontogenetic variation in diet as a result of a shift from flies to beetles with increasing body size of frogs, but there were no differences in diet between males and females. We also found evidence of individual specialization, which varied seasonally together with population trophic niche width; during the warm season (October-March), individual specialization and population TNW both increased.