Resource Partitioning Hypothesis Research Articles

Linking sexual size dimorphism to trophic niche partitioning in a generalist predator

Sexual size dimorphism is a common phenomenon in mammals, and researchers have been trying to demonstrate the evolutionary causes leading to sexual dimorphism. Two main hypotheses emerged: (1) the sexual selection hypothesis and (2) the sexual competition hypothesis (also called resource partitioning hypothesis). Here, we attempted to link sexual dimorphism in fishers ( Pekania pennanti (Erxleben, 1777)) with their fall diet using stable isotope profiling and body and skull measurements. We used the carcasses of 39 fishers which were caught in eastern Québec during fall 2014 by volunteer trappers as well as several potential prey items ranging from small rodents to cervids. We expected minimal niche overlap between sexes, as males should be able to exploit different prey species than females. We also expected to observe an effect of age class (adults vs. juveniles) on trophic niche. As expected, we found great evidence of sexual dimorphism in both body mass and skull measurements: males were heavier and longer than females and had a larger zygomatic and intracanine width and a longer skull. While proportions of prey in diet according to sex and age did not vary greatly, we found some evidence of niche partitioning using Layman's metrics. Indeed, females tended to have a less diversified and more similar diet compared to one another, whereas males showed more diversified and contrasted diets. Despite our limited sample size, our findings provide partial support to the sexual competition hypothesis, as the difference in body and skull size based on sex could have evolved to lessen intraspecific competition in fishers.

Inter-cluster competition and resource partitioning may govern the ecology of Frankia.

Microbes live in a complex communal ecosystem. The structural complexity of microbial community reflects diversity, functionality, as well as habitat type. Delineation of ecologically important microbial populations along with exploration of their roles in environmental adaptation or host-microbe interaction has a crucial role in modern microbiology. In this scenario, reverse ecology (the use of genomics to study ecology) plays a pivotal role. Since the co-existence of two different genera in one small niche should maintain a strict direct interaction, it will be interesting to utilize the concept of reverse ecology in this scenario. Here, we exploited an 'R' package, the RevEcoR, to resolve the issue of co-existing microbes which are proven to be a crucial tool for identifying the nature of their relationship (competition or complementation) persisting among them. Our target organism here is Frankia, a nitrogen-fixing actinobacterium popular for its genetic and host-specific nature. According to their plant host, Frankia has already been sub-divided into four clusters C-I, C-II, C-III, and C-IV. Our results revealed a strong competing nature of CI Frankia. Among the clusters of Frankia studied, the competition index between C-I and C-III was the largest. The other interesting result was the co-occurrence of C-II and C-IV groups. It was revealed that these two groups follow the theory of resource partitioning in their lifestyle. Metabolic analysis along with their differential transporter machinery validated our hypothesis of resource partitioning among C-II and C-IV groups.

Individual‐resource network between Xylocopa bees and plant resources: generalist species, specialist individuals?

1. The resource partitioning hypothesis states that sympatric, morphologically, and functionally similar species can coexist by temporal separation or low food overlap. Also, the interindividual variations about the use of resources, i.e. individual specialisation, can promote the resilience and stability of their populations when an environmental disturbance affects food availability.2. Two sympatric and polylectic species of carpenter bees to test both the hypotheses of food niche partitioning and the occurrence of individual specialisation were used.3. The study was conducted in two Brazilian Savanna areas and the trophic niches of Xylocopa grisescens and X. frontalis were determined by the diversity of pollen types obtained from larval food samples. Individual‐resource networks were constructed to elucidate the patterns of resource use by the individuals of each species.4. The populations of the two bee species moderately overlapped their trophic niche. Xylocopa grisescens mainly used the pollen of non‐poricidal plants, whereas X. frontalis used pollen from plants with poricidal anthers. Individual‐resource networks of both species are weakly connected, highly specialised, and modular.5. In conclusion, the results suggest that the coexistence between Xylocopa grisescens and X. frontalis probably occurs due to food resource partitioning. Furthermore, the results about individual‐resource networks of both species seem to reveal the occurrence of interindividual variations regarding food resource foraging.

Non-linear relationship between body size of terrestrial carnivores and their trophic niche breadth and overlap

Studying food partitioning of mammalian predators is important for understanding trophic structures and interactions between coexisting carnivore species. This is particularly pertinent in the light of expanding ranges of populations of generalist species whose habitat and diet overlap with more specialized species. Here, we tested the resource partitioning hypothesis in terrestrial carnivores, predicting that trophic niche breadth and overlap relate positively to body mass. We used dietary data from 18 terrestrial carnivore taxa in four families (Canidae, Mustelidae, Felidae and Ursidae; body mass 0.1–173.6kg) in three regions in Central and Eastern Europe, i.e. deciduous forest and forest-steppe region (DFR), temperate deciduous and mixed forest region (MFR) and transitory mixed forest regions (TFR). We ranked carnivores along an axis of trophic niche (breadth and overlap), and analysed the relationship between trophic niche and body mass (or pair-wise difference in body mass). A hierarchical cluster analysis of diet composition divided carnivores into four ecological groups: wild ungulate predators; small-mammal predators; amphibians and small mammal predators and omnivores. The relationship between body mass of predators and both trophic niche breadth and trophic niche overlap were hump-shaped. The trophic niche breadth to body mass ratio was significantly lower in DFR than in TFR and trophic niche overlap was significantly higher in DFR than in MFR and TFR. The predominant food resource is small mammals whose abundance is related to local agricultural and forestry management practices. Modifications of management techniques can affect population dynamics and community composition of carnivore species, especially in the case of small-mammal predators.

Testing for complementarity in phosphorus resource use by mixtures of crop species

The phosphorus (P) resource partitioning hypothesis assumes that dissimilarity in P acquisition traits among plant species leads to enhanced P uptake by crop combinations compared with their sole crops. We developed and implemented a test for this hypothesis. Two pot experiments were conducted with quartz sands. In Experiment 1, the ability of the crop species to acquire P from sparingly soluble sources (Ca phosphate (CaP), phytate (PhyP) and P-coated Fe (hydr)oxide (FeP)) was tested. In accordance with the species performances in Experiment 1, combinations of millet/chickpea and cabbage/faba bean (which have dissimilar P acquisition traits) and wheat/maize (which have similar traits) were selected for Experiment 2. The biomass production and P uptake were compared between the sole crops and species combinations as well as between the single and mixed P sources. A dissimilarity in P acquisition traits enhanced P uptake by millet/chickpea on CaP/PhyP (as expected) but not by cabbage/faba bean on FeP/PhyP. Despite their similar P acquisition traits, we found enhanced P uptake by wheat/maize on CaP/PhyP. Because of complicating factors such as unstable P acquisition traits and competitive inequality between species, the conditions under which the P resource partitioning hypothesis can be tested are limited. This challenge complicates designing for complementarity in soil P pools by intercrops.

A new small captorhinid reptile from the lower Permian of Oklahoma and resource partitioning among small captorhinids in the Richards Spur fauna

AbstractTwo partial reptile skulls and six dentigerous fragments from the lower Permian Richards Spur locality of Oklahoma represent a new genus and species of small captorhinid reptile. Labidosauriscus richardi gen. et sp. nov. is distinguished from other captorhinids in the reduction of the height of the ridges forming the characteristic net‐like, ridge‐and‐pit cranial sculpturing of captorhinids, and the superimposition of a system of finer pits and furrows over the primary ridge‐and‐pit cranial ornamentation. Labidosauriscus richardi shares with C. laticeps a post‐caniniform tooth morphology characterized by convex mesial and distal carinae that form a distinctly asymmetrical apex in labial aspect. The description of L. richardi brings to six the number of captorhinid species known from the productive Richards Spur fissure‐fill locality. Each of these species exhibits a distinctive post‐caniniform tooth morphology (or multiplication of these teeth), which is consonant with the hypothesis of resource partitioning among the small faunivorous and omnivorous captorhinids at Richards Spur. As an ‘exhumed early Permian hill’, Richards Spur provides a unique window into early reptile diversification in a distinctive upland environment that is rarely preserved in the tetrapod fossil record.

Do ectotherms partition thermal resources? We still do not know.

Partitioning of the niche space is a mechanism used to explain the coexistence of similar species. Ectotherms have variable body temperatures and their body temperatures influence performance and, ultimately, fitness. Therefore, many ectotherms use behavioral thermoregulation to avoid reduced capacities associated with body temperatures far from the optimal temperature for performance. Several authors have proposed that thermal niche partitioning in response to interspecific competition is a mechanism that allows the coexistence of similar species of ectotherms. We reviewed studies on thermal resource partitioning to evaluate the evidence for this hypothesis. In almost all studies, there was insufficient evidence to conclude unequivocally that thermal resource partitioning allowed species coexistence. Future studies should include sites where species are sympatric and sites where they are allopatric to rule out alternative mechanisms that cause differences in thermal traits between coexisting species. There is evidence of conservatism in the evolution of most thermal traits across a wide range of taxa, but thermal performance curves and preferred temperatures do respond to strong selection under laboratory conditions. Thus, there is potential for selection to act on thermal traits in response to interspecific competition. Nevertheless, more stringent tests of the thermal resource partitioning hypothesis are required before we can assess whether it is widespread in communities of ectotherms in nature.

Transpiration dynamics support resource partitioning in African savanna trees and grasses

It is still far from clear whether and to what extent trees and grasses partition soil moisture in tropical savannas. A major reason for this is that we don't know how snapshot data on rooting differences translate into ecologically relevant patterns of water use at seasonal scales. We used stable isotopes in soil and stem water to quantify functional rooting profiles in grasses and two tree species in a South African savanna. Concurrently, we measured tree sap‐flow velocity, grass canopy temperature (a transpiration correlate), and soil moisture content at multiple depths over the course of a growing season. We used lasso regression to identify the dominant soil moisture layers driving daily variation in tree and grass water‐use metrics while controlling for weather variables. We found clear rooting depth differences between grasses (shallow) and trees (deep) from the isotopic data, and these patterns were strongly supported by the water‐use data, which showed that grasses and trees predominantly responded to soil moisture availability at 5 and 40 cm depth, respectively. Our results provide a rare example of mechanistic support for the resource partitioning hypothesis in savannas, with important implications for our understanding of tree–grass dynamics under altered precipitation regimes.

Morphological variation of introduced species: The case of American mink (Neovison vison) in Spain

We studied the morphology of American mink Neovison vison in five out of the six introduced populations in Spain. The spatial and temporal variation of body weight (BW), body length (BL), tail length, hind-foot length and ear length were analysed. Temporal trends in BW and BL in relation to years since mink introduction were also analyzed. In addition, we tested the effect of sex, age (juvenile, subadult and adult) and age–sex interaction, on each parameter. Morphological parameters differed between populations, illustrating the high variability of body size of American mink in different environments, and the phenotypic plasticity of the species. Annual variations were synchronized between populations, suggesting a large-scale effect on all of them. BW and BL showed a decreasing trend in both males and females in relation to years since introduction. This decrease may be related to mink's diet. Differences in sex and age were found, pointing to sexual dimorphism in adults, subadults and juveniles. The dimorphism in non-adult individuals suggests that subadult males may have a competitive advantage from subadult females in feeding and/or hunting on bigger prey from an early age (resource partitioning hypothesis).

Ontogenetic diet shifts and food partitioning between two small sympatric skates (Chondrichthyes, Rajidae) in the Southwestern Atlantic

Knowing how sympatric species partition their resources is very important for understanding the mechanisms that influence marine community structure. We test the hypothesis of resource partitioning between two sympatric, closely related, morphologically similar, small skates, Psammobatis bergi and P. extenta. The diets of the two species were different. P. bergi fed predominantly on crabs, amphipods, isopods and polychaetes. P. extenta consumed mainly amphipods and shrimps. Changes in the diet with body size, maturity stage and season varied among species. The consumption of amphipods decreased with increasing size of both species. The consumption of crabs increased with increasing size of P. bergi, but decreased with increasing size of P. extenta. The consumption of cumaceans increased with size of P. extenta and decreased with size of P. bergi. Adults preyed on isopods more heavily than juveniles for both species. P. extenta preyed on shrimps more heavily in the warm season and, on the contrary P. bergi preyed on shrimps more often in the cold season. The dietary breadth was higher in P. bergi than in P. extenta and was higher in females than in males. Our results showed that these sympatric and closely-related species have clearly different trophic traits.

Two new diminutive species of Cnemaspis Strauch 1887 (Squamata: Gekkonidae) from Peninsular Malaysia

Two new diminutive species of Cnemaspis are described from Peninsular Malaysia. Cnemaspis monachorum sp. nov. is a karst-dwelling species endemic to Pulau Langkawi, Kedah and is the smallest species of Southeast Asian Cnemaspis to date. Cnemaspis pseudomcguirei sp. nov. is a montane species known only from Bukit Larut, Perak in the Bintang Mountain Range and is very similar in appearance to the considerably larger, sympatric species C. mcguirei. Evidence supporting a working hypothesis of resource partitioning between sympatric species pairs of Cnemaspis on the basis of size and microhabitat preference is presented.

COMPETITION AMONGEUCALYPTUSTREES DEPENDS ON GENETIC VARIATION AND RESOURCE SUPPLY

Genetic variation and environmental heterogeneity fundamentally shape the interactions between plants of the same species. According to the resource partitioning hypothesis, competition between neighbors intensifies as their similarity increases. Such competition may change in response to increasing supplies of limiting resources. We tested the resource partitioning hypothesis in stands of genetically identical (clone-origin) and genetically diverse (seed-origin) Eucalyptus trees with different water and nutrient supplies, using individual-based tree growth models. We found that genetic variation greatly reduced competitive interactions between neighboring trees, supporting the resource partitioning hypothesis. The importance of genetic variation for Eucalyptus growth patterns depended strongly on local stand structure and focal tree size. This suggests that spatial and temporal variation in the strength of species interactions leads to reversals in the growth rank of seed-origin and clone-origin trees. This study is one of the first to experimentally test the resource partitioning hypothesis for intergenotypic vs. intragenotypic interactions in trees. We provide evidence that variation at the level of genes, and not just species, is functionally important for driving individual and community-level processes in forested ecosystems.

Spatial Patterns of Sexual Dimorphism in Minks (Mustela vison)

Spatial patterns of sexual dimorphism in minks (Mustela vison) from 35 localities in North America were examined using 25 cranial characters to test predictions of the resource partitioning hypothesis of sexual dimorphism. Specific hypotheses evaluated were that trophic structures would be among the most dimorphic and would not be strongly correlated to body size characters. Twenty of 25 characters were significantly larger in males. Predictions of the resource partitioning hypothesis were not supported as canine diameter, a widely used indicator of resource partitioning, was not sexually dimorphic and there was a relatively large correlation between body size traits and trophic traits. Significant spatial variation in degree of dimorphism was found. The patterns of sexual dimorphism from principal components analysis indicated that largest degrees of sexual dimorphism were found in minks from Pennsylvania and Florida and least degrees of dimorphism were in minks from Alaska and Quebec. Sexual dimorphism may have an important temporal component which should be investigated in further studies.

Resource partitioning among British and Irish mustelids

summary Seven species of mustelid carnivore live in the British Isles: weasel, stoat, mink, polecat, pine marten, badger and otter. Recent studies have hypothesized that coexistence of these species is facilitated by partitioning of resources according to prey size, particularly that of mammalian prey. This hypothesis has been supported by evidence of character displacement derived from even size ratios in skull length and canine diameter. To test whether this hypothesis is supported by empirical data, 98 studies of the diet of mustelids living in Great Britain and Ireland were analysed. Two main predictions were tested; that larger males ate larger prey than females and that larger species ate larger prey than smaller species. Male mustelids ate larger prey than females but there was no relationship between predator size and prey size, either for all species or when largely vermivorous badgers and piscivorous otters were excluded. There was no difference in dietary niche breadth between the sexes. Dietary niche breadth increased with body size in the assemblage excluding otters and badgers. The dietary niches of mustelids were partitioned along several axes, none of which was clearly related to prey size. The dietary niches of the five species living in Ireland (stoat, mink, pine marten, otter and badger) were more similar to one another in Ireland than in Great Britain and there was no difference in niche breadth between Irish and British mustelids. There was no evidence of competitive release in the diets of Irish mustelids. Resource partitioning according to prey size is apparent between the sexes within species, and this is probably correlated to sexual selection for size dimorphism. Empirical data do not, however, support a hypothesis of resource partitioning according to prey size between species. Interspecific aggression provides an alternative hypothesis explaining character displacement among mustelids.

The Founding of Specialist Firms in a Global Fragmenting Industry

The study examines what drives the founding of specialist firms. Two theoretical explanations are tested for the founding of specialists: density dependence and resource partitioning. The study finds that specialists' foundings are dependent on the population's density at the global level, but not at the United States level. The evidence from a fragmented industry does not support the resource partitioning hypothesis, either at the global level or the United States national level. The study shows how multi-level analyses can suggest if an industry is multi-domestic or globally integrated.

Neighbor Relatedness and Competitive Performance in Impatiens capensis (Balsaminaceae): A Test of the Resource Partitioning Hypothesis

The Elbow Room hypothesis for the maintenance of sex depends upon the assumption that intraspecific resource partitioning occurs and increases in magnitude with decreasing genetic similarity of competitors. This assumption leads to the prediction that plants should have greater fitness in competition with nonrelatives than in competition with siblings. Moreover, if a population displays fine scale genetic structure and genetic similarity declines with distance, then resource partitioning should increase with increasing geographical distance between the source locations of the competing genotypes. We tested these predictions in a greenhouse experiment by subjecting inbred Impatiens capensis seedlings to four types of competitors: 1) inbred full sibs; 2) inbred nonrelatives from the same source location; 3) inbred nonrelatives from a source location 30 m away; and 4) inbred nonrelatives from another population approximately 1 km distant. Plant dry weight at harvest increased significantly with seed weight and earlier emergence date, decreased significantly with seed weight and earlier emergence date of the competitor, and varied significantly among maternal seed families. However, there was no significant effect of competitor relatedness or distance between parental locations. The experiment therefore failed to support the resource partitioning hypothesis.

NEIGHBOR RELATEDNESS AND COMPETITIVE PERFORMANCE IN IMPATIENS CAPENSIS (BALSAMINACEAE): A TEST OF THE RESOURCE PARTITIONING HYPOTHESIS

The Elbow Room hypothesis for the maintenance of sex depends upon the assumption that intraspecific resource partitioning occurs and increases in magnitude with decreasing genetic similarity of competitors. This assumption leads to the prediction that plants should have greater fitness in competition with nonrelatives than in competition with siblings. Moreover, if a population displays fine scale genetic structure and genetic similarity declines with distance, then resource partitioning should increase with increasing geographical distance between the source locations of the competing genotypes. We tested these predictions in a greenhouse experiment by subjecting inbred Impatiens capensis seedlings to four types of competitors: 1) inbred full sibs; 2) inbred nonrelatives from the same source location; 3) inbred nonrelatives from a source location 30 m away; and 4) inbred nonrelatives from another population approximately 1 km distant. Plant dry weight at harvest increased significantly with seed weight and earlier emergence date, decreased significantly with seed weight and earlier emergence date of the competitor, and varied significantly among maternal seed families. However, there was no significant effect of competitor relatedness or distance between parental locations. The experiment therefore failed to support the resource partitioning hypothesis.