Mechanisms Of Resource Partitioning Research Articles

Smaller islands, bigger appetites: evolutionary strategies of insular endemic skinks.

Competitive dietary and morphological divergence among co-occurring species are fundamental aspects of ecological communities, particularly on islands. Cabo Verde (~570 km west of continental Africa) hosts several endemic reptiles descended from common ancestors, with sympatric species exhibiting wide morphological variation and competing for limited resources. To explore the mechanisms of resource partitioning between coexisting species, DNA metabarcoding was used to compare the diets of large and small skinks, Chioninia vaillantii and Chioninia delalandii, in sympatric and allopatric contexts on Fogo Island and in a more competitive context on the small and resource-poor Cima Islet. The morphological variation of all populations was also examined to test the character displacement hypothesis and to compare the effect of different competitive scenarios. Results showed significant differences in diet and linear measurements between species and populations. The two sympatric populations of C. delalandii on Fogo and Cima showed similar changes in head morphology compared to the allopatric population, supporting character displacement. The effect of higher competitive pressure on Cima was evidenced by the increased morphological and dietary variation observed. This study demonstrates how sister species develop dietary adaptations/morphologies to maintain stable coexistence, especially in highly competitive scenarios, providing useful insights for effective conservation strategies.

Living with voracious roommates: Factors that explain isotopic niche variation in a mixed colony of insectivorous bats.

Theory predicts that in resource-limited environments, coexisting species may overlap their niche dimensions but must differ in at least one to avoid competitive exclusion. Specifically, it has been suggested that the coexistence of competing species within a guild, could be sustained with mechanisms of resource partitioning, such as segregation along a trophic dimension. Among the most gregarious mammals are bats, which present diversification in their diet based on habitat choice and body size. Despite differences that could explain specialization in prey selection, there are insufficient studies that explore food overlap in mixed bat colonies and the factors that determine the selection of prey, both at intra- and inter-specific levels. To fill this gap, we analyzed the isotope signal (δ13C and δ15N) in feces collected in a mixed colony of Tadarida brasiliensis and Myotis chiloensis. To understand how several factors could influence these isotopic signals, intrinsic explanatory variables were analyzed, including body mass, body length, age, and sex. Also, extrinsic variables were analyzed, including monthly temporality and moonlight intensity. Our findings support age-dependent specialization in M. chiloensis, with a significant role of moonlight intensity and sex on δ15N. In T. brasiliensis, we identified a significant effect of size, sex, and ear length on δ15N. Our analysis indicates that both species of bats experience diverse degrees of overlap through austral summer months, affected by several factors that explain the variability in their fecal isotopic signals.

The generality of cryptic dietary niche differences in diverse large-herbivore assemblages

Ecological niche differences are necessary for stable species coexistence but are often difficult to discern. Models of dietary niche differentiation in large mammalian herbivores invoke the quality, quantity, and spatiotemporal distribution of plant tissues and growth forms but are agnostic toward food plant species identity. Empirical support for these models is variable, suggesting that additional mechanisms of resource partitioning may be important in sustaining large-herbivore diversity in African savannas. We used DNA metabarcoding to conduct a taxonomically explicit analysis of large-herbivore diets across southeastern Africa, analyzing ∼4,000 fecal samples of 30 species from 10 sites in seven countries over 6 y. We detected 893 food plant taxa from 124 families, but just two families-grasses and legumes-accounted for the majority of herbivore diets. Nonetheless, herbivore species almost invariably partitioned food plant taxa; diet composition differed significantly in 97% of pairwise comparisons between sympatric species, and dissimilarity was pronounced even between the strictest grazers (grass eaters), strictest browsers (nongrass eaters), and closest relatives at each site. Niche differentiation was weakest in an ecosystem recovering from catastrophic defaunation, indicating that food plant partitioning is driven by species interactions, and was stronger at low rainfall, as expected if interspecific competition is a predominant driver. Diets differed more between browsers than grazers, which predictably shaped community organization: Grazer-dominated trophic networks had higher nestedness and lower modularity. That dietary differentiation is structured along taxonomic lines complements prior work on how herbivores partition plant parts and patches and suggests that common mechanisms govern herbivore coexistence and community assembly in savannas.

Is resource partitioning between two sympatric species of Gracilinanus (Didelphimorphia: Didelphidae) related to trophic and spatial niches?

Abstract Small mammal species may occur in sympatry, and it is relevant to investigate the mechanisms that lead to coexistence of the closely related species. Despite this, studies evaluating the coexistence of closely related Neotropical marsupials are insipient. The aim of this study was to analyse the mechanisms of resource partitioning between the sympatric species of mouse opossums Gracilinanus agilis and G. microtarsus (Didelphidae), evaluating their trophic and spatial niche. We hypothesized that G. agilis and G. microtarsus differ in at least one niche dimension (space use or food preferences) as a mechanism of coexistence. In the study we analysed trophic niche by evaluating the frequency of occurrence of food items present in Gracilinanus faeces. Also, we analysed spatial niche by comparing the vegetal stratum where the individuals were captured and its relationship with the environmental complexity. Both species presented a high trophic niche overlap, with differences in the frequencies of occurrence of the consumed items. Although the most frequent items in the faeces were Hymenoptera, Isoptera and Coleoptera, their proportion differed significantly between the two species. The variety of food items also differed, with flowers being more frequent in G. agilis diet, whereas fruits were more recorded for G. microtarsus. The spatial niche was very similar, with both species being more captured in the forest understory. However, habitat complexity influenced the abundance of both species, especially litter depth and its biomass of leaves. The results indicated that the coexistence of the two species is associated with the trophic and spatial niche, and that this niche segregation could be allowing closely related species of Gracilinanus to coexist.

Food for everyone: Differential feeding habits of cryptic bat species inferred from DNA metabarcoding.

Ecological theory postulates that niches of co‐occurring species must differ along some ecological dimensions in order to allow their stable coexistence. Yet, many biological systems challenge this competitive exclusion principle. Insectivorous bats from the Northern Hemisphere typically form local assemblages of multiple species sharing highly similar functional traits and pertaining to identical feeding guilds. Although their trophic niche can be accessed with unprecedented details using genetic identification of prey, the underlying mechanisms of resource partitioning remain vastly unexplored. Here, we studied the differential diet of three closely‐related bat species of the genus Plecotus in sympatry and throughout their entire breeding season using DNA metabarcoding. Even at such a small geographic scale, we identified strong seasonal and spatial variation of their diet composition at both intra‐ and interspecific levels. Indeed, while the different bats fed on a distinct array of prey during spring, they showed higher trophic niche overlap during summer and fall, when all three species switched their hunting behaviour to feed on few temporarily abundant moths. By recovering 19 ecological traits for over 600 prey species, we further inferred that each bat species used different feeding grounds and hunting techniques, suggesting that niche partitioning was primarily habitat‐driven. The two most‐closely related bat species exhibited very distinct foraging habitat preferences, while the third, more distantly‐related species was more generalist. These results highlight the need of temporally comprehensive samples to fully understand species coexistence, and that valuable information can be derived from the taxonomic identity of prey obtained by metabarcoding approaches.

Interspecific aggression in sympatry between congeneric tropical birds

AbstractInterspecific aggression may shape species distributions through competitive exclusion, resulting in spatial segregation, or facilitate sympatry as an adaptive mechanism for resource partitioning. Competitive exclusion results from asymmetric aggression of one species towards another, but if the aggressive relationship between species is symmetric, they may persist in sympatry. Interspecific aggression is widely cited as a mechanism for maintaining the distributional limits of tropical birds, but how it shapes the spatial dynamics of competing species that are sympatric over larger geographic areas is less clear. To address this issue, we conducted reciprocal playback experiments on two congeneric Antbirds — Thamnophilus atrinucha and T. doliatus — that occur in sympatry across a habitat matrix in Colombia to characterize their relationship as symmetrically or asymmetrically aggressive and analyzed point count data to assess the degree to which they occur sympatrically. We found weak evidence for competitive exclusion, with the larger T. doliatus responding asymmetrically to T. atrinucha, and the two species having a low co-detection rate during point counts. However, despite their 22% difference in body size, T. atrinucha still responded to T. doliatus playback in over half of our trials, and the two species co-occurred on nearly 25% of point counts, indicating that interspecific aggression does not drive complete spatial segregation. Our findings highlight how the degree to which one species can competitively exclude another may vary, especially across a dynamic landscape.

Clutter negotiating ability in an ensemble of forest interior bats is driven by body mass.

Differences in wing morphology are predicted to reflect differences in bat foraging strategies. Experimental tests of this prediction typically assess the relationship between wing morphology and a measures of flight performance on an obstacle course. However, studies have lacked measures of obstacle avoidance ability true scores, which may confound interpretation of ability across the range of presented tasks. Here, we used Rasch analysis of performance in a collision-avoidance experiment to estimate the ability of bat species to fly through vegetative clutter. We refer to this latent trait as 'clutter negotiating ability' and determined the relationships between clutter negotiating ability and wing morphology in 15 forest insectivorous bat species that forage in the densely cluttered rainforests of Malaysia. The clutter negotiating ability scores were quantified based on individual responses of each species to 11 different obstacle arrangements (four banks of vertical strings 10-60 cm apart). The tasks employed for the collision-avoidance experiment were reliable and valid, although Rasch analysis suggested that the experiment was too easy to discriminate completely among the 15 species. We found significant negative correlations between clutter negotiating ability and body mass, wingspan, wing loading and wing area but a positive significant correlation with wingtip area ratio. However, in stepwise multiple regression analyses, only body mass and wing loading were significant predictors of clutter negotiating ability. Species fell into clusters of different clutter negotiating ability, suggesting a potential mechanism for resource partitioning within the forest interior insectivorous ensemble.

Old at Heart, Young at the Periphery: An Age-Dependence Approach to Resource Partitioning

This study examines how the age of categories and organizations within an industry affects the likelihood of de novo entry. Whereas previous literature on age dependence focused on the effects of aging for individual organizations, we analyze how aging processes drive the evolution of markets. We offer an age-related explanation for the mechanism of resource partitioning, i.e., the relative increase in the number of new entrants in a market’s periphery as a result of increasing concentration among central incumbents. We theorize that, as the incumbents within a category grow older, their capacity to undertake structural changes diminishes: coupled with evolving audience preferences, this generates a gap between what the incumbents are capable to offer and what the audience demands, hence creating opportunities for new entrants to step into the market. We also conjecture that such entry opportunities are more likely in younger categories, where the audience’s preferences change more rapidly. We test our arguments through a longitudinal study of market segments in the recording industry.

Nitrogen uptake pattern of herbaceous plants: coping strategies in altered neighbor species

The mechanisms for maintaining the species diversity of plant communities under conditions of resource limitation is an important subject in ecology. How interspecific relationships influence the pattern of nutrient absorption by coexisting species in N-limited ecosystems is still disputed. We investigated the effect of neighbor species on the uptake of inorganic and organic N by three common plant species using 15N tracer techniques in a semi-arid alpine steppe on the northern Tibet. The results showed that the plant species varied in their capacity to absorb NO3 −-N, NH4 +-N, and glycine-N with or without neighbor species. Carex moorcroftii and Leontopodium nanum showed much more plasticity in resource utilization than Stipa purpurea when neighbor species were present. When C. moorcroftii and S. purpurea coexisted, they all increased their 15N uptake for the NO3 −-N (C. moorcroftii 2.2-fold increase and S. purpurea 2.2-fold increase) and glycine-N treatments (C. moorcroftii 2.9-fold increase and S. purpurea 3.4-fold increase), which indicated that neighborhood had a positive effect for N absorption between the two species. However, L. nanum was a less effective competitor for N utilization than the neighbor species across almost all treatments. The dominant species appeared to have an inhibitory effect on N absorption by the accompanying species in this alpine steppe environment. Thus, interspecific neighbor pairs may result in both a mutually beneficial cooperative relationship and a competitive relationship among neighbors in resource use patterns in extreme environments. Resource use plasticity in altered neighbor species may be due to phenotypic plasticity based on the conditions of the realized niche, offering a valuable insight into niche complementarity and providing a general and important mechanism for resource partitioning in an alpine area.

Coexistence of three sympatric cormorants (Phalacrocorax spp.); partitioning of time as an ecological resource.

Resource partitioning is well known along food and habitat for reducing competition among sympatric species, yet a study on temporal partitioning as a viable basis for reducing resource competition is not empirically investigated. Here, I attempt to identify the mechanism of temporal partitioning by intra- and interspecific diving analyses of three sympatric cormorant species at different freshwater wetlands around the Delhi region. Diving results indicated that cormorants opted for a shallow diving; consequently, they did not face any physiological stress. Moreover, diving durations were linked with seasons, foraging time and foraging habitats. Intraspecific comparison suggested that cormorants spent a longer time underwater in early hours of the day. Therefore, time spent for dive was higher in the forenoon than late afternoon, and the interspecific analysis also yielded a similar result. When Phalacrocorax niger and Phalacrocorax fuscicollis shared the same foraging habitat, they tended to differ in their foraging time (forenoon/afternoon). However, when P. niger and Phalacrocorax carbo shared the same foraging time, they tended to use different foraging habitats (lentic/lotic) leading to a mechanism of resource partitioning. Thus, sympatric cormorants effectively use time as a resource to exploit the food resources and successful coexistence.

Resource Partitioning and Niche Overlap in Three Sympatric Species of Dragonflies (Anisoptera Libellulidae) in Anuradhapura District, Sri Lanka

Resource partitioning in ecological communities bears profound connection with the coexistence of closely related species. As a mechanism, it assists species with similar characteristics to thrive in the environments where they can utilise resources in different levels in spatial and temporal scale via niche partitioning. As ecologically important insects, dragonflies are well-studied in many aspects globally but poorly assessed locally. The current study was conducted under the main objective of identifying the mechanism of resource partitioning in three sympatric most common skimmer species; Brachythemis contaminata , Crocothemis servilia servilia and Rhyothemis variegata variegata in two tank ecosystems in Anuradhapura district, Sri Lanka. The study was conducted from May-August 2014 simultaneously in Nabadagaswewa tank (NW) and Mihintale tank (MT). Data collection was carried out 08:00 to 10:00 hrs in the morning and 13:00 to 15:00 hrs in the evening. Land-water interface at the tank was used for the study in both sites. Scan sampling was used to obtain data on resource utilisation by the three skimmer species. Randomly selected individuals were observed for 30 seconds in each observation point. Vegetation variables (bank vegetation density and height, aquatic vegetation density and height) were measured using two belt transects (25×1 m2) in both habitats. The three species were more active in the morning hours (08:00 to 10:00 hrs) and shows different levels of perch and fly heights in the morning and evening hours. R.v. variegata was recorded using heights of <100 cm in both habitats. B. contaminata and C.s. servilia showed high spatial niche overlap (Oij=0.716) in NW and in MT highest spatial niche overlap was observed between C.s. servilia and R.v. variegata (Oij=0.473). The broadest niche breadth was exhibited by C.s. servilia (B=0.46) in NW while B. contaminata showed the highest (B=0.23) in MT. R.v. variegata showed the lowest niche breadth in both habitats (NW: B = 0.39, MT: B=0.09). Relationship between the species abundance and vegetation heights and densities shows that vegetation height and bank vegetation densities were negatively correlated with the abundance of the three skimmer species. This study depicts ways of resource partitioning among the three sympatric skimmer species minimising interspecific competition and favoring their co-existence. Further, it highlights the extent of spatial niche overlap is influenced by the habitat characteristics especially the vegetation structure and resource availability. Keywords: Resource partitioning, Niche overlap, Libellulidae

Coexistence of oceanic predators on wintering areas explained by population‐scale foraging segregation in space or time

Ecological niche theory predicts segregation mechanisms that mitigate potential competition between closely related organisms. However, little is known outside the breeding season, when central-place foraging animals may move on larger scales. This study tested for segregation mechanisms within the same 2007 inter-breeding period on three neighboring populations of avian predators from the southern Indian Ocean: Eastern Rockhopper Penguins Eudyptes filholi from Crozet and Kerguelen and Northern Rockhopper Penguins E. moseleyi from Amsterdam. Using state-of-the-art geolocation tracking and stable isotope analysis techniques, we quantified and compared the ecological niches in time, space, and diet. The three populations showed large-scale movements over deep oceanic waters near the Subantarctic Front, with generally little individual variation. The two neighboring populations of Eastern Rockhopper Penguins showed strikingly distinct distribution in space, while foraging in similar habitats and at the same trophic level (crustacean-eaters). In contrast, Northern Rockhoppers showed marked spatial overlap with birds of the sibling Eastern species, but their temporal delay of two months enabled them to effectively avoid significant overlap. Our results highlight parsimonious mechanisms of resource partitioning operating at the population level that may explain how animals from neighboring localities can coexist during the nonbreeding period.

The ontogenetic scaling of bite force and head size in loggerhead sea turtles (Caretta caretta): implications for durophagy in neritic, benthic habitats

Ontogenetic studies of vertebrate feeding performance can help address questions relevant to foraging ecology. Feeding morphology and performance can either limit access to food resources or open up new trophic niches in both aquatic and terrestrial systems. Loggerhead sea turtles are long-lived vertebrates with complex life histories that are marked by an ontogenetic shift from an oceanic habitat to a coastal neritic habitat, and a transition from soft oceanic prey to hard, benthic prey. Although considered durophagous and strong biters, bite performance has not been measured in loggerheads, nor has the ontogeny of bite performance been characterized. In the present study, we collected measurements of bite force in loggerhead turtles from hatchlings to adults. When subadults reach the body size at which the ontogenetic shift occurs, their crushing capability is great enough for them to consume numerous species of hard benthic prey of small sizes. As loggerheads mature and bite performance increases, larger and harder benthic prey become accessible. Loggerhead bite performance eventually surpasses the crushing capability of other durophagous carnivores, thereby potentially reducing competition for hard benthic prey. The increasing bite performance and accompanying changes in morphology of the head and jaws are likely an effective mechanism for resource partitioning and decreasing trophic competition. Simultaneous measurements of body and head size and the use of non-linear reduced major axis regression show that bite force increases with significant positive allometry relative to body size (straight carapace length, straight carapace width and mass) and head size (head width, height and length). Simple correlation showed that all recorded morphometrics were good predictors of measured bite performance, but an AICc-based weighted regression showed that body size (straight carapace width followed by straight carapace length and mass, respectively) were more likely predictors of bite force than head size morphometrics (head width and head length).

High‐throughput sequencing offers insight into mechanisms of resource partitioning in cryptic bat species

Sympatric cryptic species, characterized by low morphological differentiation, pose a challenge to understanding the role of interspecific competition in structuring ecological communities. We used traditional (morphological) and novel molecular methods of diet analysis to study the diet of two cryptic bat species that are sympatric in southern England (Plecotus austriacus and P. auritus) (Fig. 1). Using Roche FLX 454 (Roche, Basel, CH) high-throughput sequencing (HTS) and uniquely tagged generic arthropod primers, we identified 142 prey Molecular Operational Taxonomic Units (MOTUs) in the diet of the cryptic bats, 60% of which were assigned to a likely species or genus. The findings from the molecular study supported the results of microscopic analyses in showing that the diets of both species were dominated by lepidopterans. However, HTS provided a sufficiently high resolution of prey identification to determine fine-scale differences in resource use. Although both bat species appeared to have a generalist diet, eared-moths from the family Noctuidae were the main prey consumed. Interspecific niche overlap was greater than expected by chance (Ojk = 0.72, P < 0.001) due to overlap in the consumption of the more common prey species. Yet, habitat associations of nongeneralist prey species found in the diets corresponded to those of their respective bat predator (grasslands for P. austriacus, and woodland for P. auritus). Overlap in common dietary resource use combined with differential specialist prey habitat associations suggests that habitat partitioning is the primary mechanism of coexistence. The performance of HTS is discussed in relation to previous methods of molecular and morphological diet analysis. By enabling species-level identification of dietary components, the application of DNA sequencing to diet analysis allows a more comprehensive comparison of the diet of sympatric cryptic species, and therefore can be an important tool for determining fine-scale mechanisms of coexistence.

Importance of resource selection and social behavior to partitioning of hostile space by sympatric canids

Investigations into mechanisms of resource partitioning are particularly suited to systems where nascent interactive behaviors are observable. Wolf (Canis lupus) recolonization of the Greater Yellowstone Ecosystem provided such a system, and we were able to identify behaviors influencing the partitioning of resources by coyotes (Canis latrans) and wolves. We observed coyote-wolf interactions immediately after wolf recolonization, when reemergent behaviors mediating the outcome of competitive interactions were detectable and mechanisms of spatial avoidance were identifiable. Although coyotes used the same space as wolves, they likely minimized risk of encounter by making adaptive changes in resource selection based on perception of wolf activity and potential scavenging opportunities. When exploiting carrion subsidies (i.e., wolf-killed ungulates), coyotes relied on social behaviors (i.e., numerical advantage in concert with heightened aggression) to mitigate escalating risk from wolves and increase resource-holding potential. By adapting behaviors to fluctuating risk, coyotes might reduce the amplitude of competitive asymmetries. We concluded coyotes do not perceive wolves as a threat requiring generalized spatial avoidance. Rather, the threat of aggressive interactions with wolves is spatially discrete and primarily contained to areas adjacent to carrion resources.

A kaleidoscope of mammal, bird and fish: habitat use patterns of top predators and their prey in Florida Bay

Habitat selection by top predators that are largely free from predation pressures is a function of prey availability and interspecific competition. Such competition can be minimized through niche dimensions: mechanism of resource partitioning based on prey choice and foraging tactic. This study compared habitat use patterns of 5 top predators (bottlenose dolphins, double- crested cormorants, osprey, brown pelicans and terns) within Florida Bay with respect to each other, their prey and habitat variability. Foraging dolphins, osprey and pelicans exhibited similar habitat use patterns in shallow, turbid, productive waters with high proportions of mud and mudbank bottom types. These same habitat characteristics also described the distribution of their major prey items: mullet and catfish. Competition between these 3 predators is likely diluted by foraging tactic varia- tion. Conversely, the habitat use patterns of cormorants showed strongest association with deeper water, with low chlorophyll a and turbidity levels, less mud and mudbank habitat, and greater pro- portions of hardbottom and seagrass bottoms. Those prey items of cormorants with less competition from other predators examined displayed the same habitat associations. Cormorants in Florida Bay may concentrate their foraging efforts on less competitive prey, occurring more frequently in habitats where these prey items dominate. Despite Florida Bay's limited bathymetric relief, habitat use pat- terns of top predators are significantly influenced by depth, and subsequently bottom type. Sighting rates of all predators, except non-foraging dolphins, peaked in shallow mudbank habitats. This pat- tern of strong habitat overlap among predators implies currently adequate resource availability and/or niche dimensions among interspecific competitors.

Coyotes and recolonizing wolves: social rank mediates risk-conditional behaviour at ungulate carcasses

Wolf, Canis lupus, recolonization of the Greater Yellowstone Ecosystem provides a rare opportunity to identify behaviours facilitating coexistence between sympatric canids. We investigated interactions between coyotes, Canis latrans, and recolonizing wolves at ungulate carcasses in Montana's Madison Range. We used a field-experimental study design consisting of a two-level carcass treatment (wolf presence, wolf absence) to assess factors influencing coyote risk assessment, carrion consumption and aggressive encounters with wolves. Socially dominant coyotes (alphas and betas) responded to wolf presence by increasing the proportion of time spent vigilant while scavenging. Vigilance behaviour was more pronounced when scavenging closer to structurally complex vegetation where lateral occlusion inhibited the ability of coyotes to scan for, and possibly escape from, returning wolves. Despite greater time spent vigilant, alpha coyotes consumed the greatest amount of carrion biomass by feeding on carcasses in earlier stages of consumption when organs and large muscle tissues were still present. This finding suggests that alpha coyotes might trade off greater risk for higher-quality food items. Coyotes would aggressively confront wolves: numerical advantage by coyotes and the stage of carcass consumption were influential in determining whether coyotes were able to displace wolves from carcasses. Coyotes relied on a gradient of risk-sensitive behaviours, ranging from elevated vigilance to aggressive confrontation, to manage risk associated with wolf presence. Identification of these behaviours, and their sensitivity to numeric and social factors, is an important step in elucidating mechanisms of resource partitioning in social canids.

Biogeographical distribution and natural groupings among five sympatric wild cats in tropical South Asia

Small to large carnivorous mammals in the tropical belt face extinction at an unprecedented rate. The vanishing of sympatric wild cats appears to be due to habitat fragmentation, human encroachment & poaching. The focus of this study is on ecological and distributional parameters that influence the wild cat communities in tropical South Asia. The distributional data for five sympatric cats is analyzed with the aim of understanding the species-habitat association under a conceptually unified binary-matrix framework. The use of cluster analysis techniques in this ecological study have helped to reveal the natural groupings among felid guilds and their ecological resource partitioning mechanism in shared habitats.

Niche overlap and resource partitioning between two sympatric fox species in southern Brazil

AbstractMechanisms that favour the co‐occurrence of morphologically and ecologically similar species in South America are potentially relevant, because two or more species often occur in sympatry. In the present study, we investigated possible mechanisms of resource partitioning between two sympatric species of foxes, the crab‐eating foxCerdocyon thousand the pampas foxPseudalopex gymnocercus, in the National Park of Aparados da Serra in southern Brazil (29°10′S, 50°05′W). We considered three main niche dimensions – habitat, diet and time – and evaluated the overlap between the two species in these dimensions. We conducted the study from June 2000 to October 2001 in an area composed of open grasslands andAraucariaforests. We studied the foxes by using a combination of scat analysis and direct observation. A comparison of their diet indicated that it was very similar for both species in all seasons (Pianka's indexes ranging from 0.920 to 0.957). The most common food item for both species of foxes was rodents, followed by coleopterans, birds and plant remains (seeds and fruits). As expected by the niche‐complementarity hypothesis, we detected differences along other niche axes.Pseudalopex gymnocercusseemed to occur only in open areas, including grasslands and dirt roads, whereasC. thouswas more generalist in habitat use, occurring both inside and at the edge of forests. However, both fox species were common in grassland habitats, where they might compete for resources. The differences were more marked for activity time, with the crab‐eating fox being significantly more nocturnal (circular mean of time of sighting=23:39 h,se=56 min) than the pampas fox (circular mean=19:56 h,se=64 min; Watson'sF=6.06,P=0.02). We suggest that the largerC.thouscould be limiting the activity ofP.gymnocercusby interference competition.

Habitat selection as a mechanism of resource partitioning in two cryptic bat species Pipistrellus pipistrellus and Pipistrellus pygmaeus

Ecomorphological studies of bat communities often reveal the spatial and temporal coexistence of morphologically similar species, leading to suggestions that these communities are structured by non‐deterministic processes. However, the diversification of echolocation call structure in bats allows for considerable morphological similarity while still permitting niche differentiation based on specialisation for prey type and habitat structure. The recent separation of a common Palaearctic bat, the pipistrelle, into Pipistrellus pipistrellus and P. pygmaeus, which are sympatrically distributed throughout their range, raises the question as to whether these two morphologically similar species partition resources in time and space.To test the hypothesis that the coexistence of these cryptic species is facilitated by differential habitat use, 14 P. pipistrellus, and 12 P. pygmaeus were radio‐tracked from adjacent maternity roosts, in northeast Scotland, from May to September 2002/2003. The two species showed distinct habitat partitioning with P. pygmaeus foraging predominantly in riparian woodland and over water, and P. pipistrellus foraging along woodland edges and short isolated tree lines. Inter‐specific overlap in habitat use was low and consequently foraging ranges were segregated spatially.The degree of habitat partitioning revealed in these species, which show considerable overlap in echolocation call parameters and functional morphology, suggests that morphological features, whilst useful in separating chiropteran species into coarse‐grained foraging guilds, may not predict fine‐grained ecological segregation.