Mechanisms of species coexistence: a field test of theoretical models using intertidal snails

Competitor coexistence is often facilitated by spatial segregation. Traditionally, spatial segregation is predicted to occur when species differ in the habitat in which they are either superior at competing for resources or less susceptible to predation. However, predictions from a behavioural model demonstrate that spatial segregation and coexistence can also occur in the absence of such interspecific trade‐offs in competitive ability and vulnerability to predation. Unlike other models of competitor coexistence this model predicts that when species rank both habitat productivity and ‘riskinesses’ similarly, but differ slightly in their habitat‐specific vulnerabilities to predators, they will tend to segregate across habitats, with the species experiencing the higher ratio of mortality risk across the habitats occurring primarily in the safer habitat. Here, we investigate the hypothesis that intraspecific trade‐offs between resource availability and mortality risk can lead to spatial segregation of competing species by (1) documenting the spatial (i.e. intertidal) distribution of two marine snails, Littorina sitkana and L. subrotundata and (2) performing field experiments to quantify growth and mortality rates of each species at ‘low’ and ‘high’ intertidal heights. Our results indicate that both species agree on the rankings of habitat riskiness and productivity, experiencing higher predation and higher growth in low‐ than in high‐intertidal habitats. However, L. sitkana and L. subrotundata experienced differences in their habitat‐specific mortality risks and growth rates. Despite both species being similarly at risk of predation in high‐intertidal habitats (where mortality was lower), L. subrotundata was subject to significantly higher mortality than L. sitkana at the low‐intertidal height. In contrast, growth rate differences between habitats were greater for L. sitkana than for L. subrotundata. Whereas both species grew at the same rate at the high‐intertidal level (where growth was lower), L. sitkana individuals grew more rapidly than L. subrotundata snails at the low‐intertidal level. As predicted by the behavioural model, the species that experienced the higher ratio of mortality across habitats (i.e. L. subrotundata) occurred exclusively in the safer, high‐intertidal habitat. Taken together, these results provide support for the hypothesis that spatial segregation, and potentially competitor coexistence, can occur in the absence of interspecific trade‐offs in resource acquisition ability or vulnerability to predation.     

Demography and habitat availability in territorial occupancy of two competing species

Although metapopulation dynamics have become the focus of considerable theoretical research, little attention has been paid to its role when examining the coexistence of species. When two or more species live in the same patch network, interspecific interactions may affect their dispersal, colonization and extinction rates, and it may be possible to incorporate competition affecting these parameters in metapopulation models. Here, we extend the territorial occupancy model proposed by Lande to competing species. Our model estimates an equilibrium proportion of habitat occupancy as a function of life‐history parameters, dispersal behavior, habitat suitability and interspecific interactions. Moreover, it could prove to be useful as a tool in the assessment of potential management decisions. We apply the model to the golden Aquila chrysaetos and the Bonelli's eagle Hieraaetus fasciatus, two territorial raptors that coexist in the Mediterranean region, sharing food and nesting habitats. Over the last twenty years, while the golden eagle has maintained and, in some cases, increased its breeding numbers, Bonelli's eagle has suffered a marked decline, with many territories abandoned by the latter now occupied by the former. This suggests that the dynamics of these species could be influenced by interspecific competition. The model identified the relative importance of competition (stable equilibrium that allows long‐term coexistence) and predicted that, when habitat overlap is slight as in the study area, intraspecific dynamics are much more important for the persistence of each species than interspecific ones. Our results suggest that the improvement of territorial bird survival and productivity are the most urgently needed actions to be undertaken in the case of the golden eagle, while for Bonelli's eagle efforts should be focused on improving territorial and non‐territorial bird survival. As habitat conservation measures, the proportion of suitable exclusive habitat should be increased for both species.     

Coexistence in Mediterranean warblers: ecological differences or interspecific territoriality?

We studied the coexistence of four species of Sylvia warblers living in Mediterranean matorral in order to identify the respective role of ecological segregation and of interspecific territoriality in explaining the local distribution of these four species. Data on habitat use, foraging behaviour and interspecific spacial segregation were collected on Corsica and on Spargi (Sardinia) islands. Despite large overlap in patch selection and in foraging behaviour the four species did segregate ecologically and behaviourally while foraging (differences in the choice of plant species used for foraging, in the height of the plant selected, in the selection of the portion of the plant volume used and in the selection of the plant structure explored). Complementarity in foraging behaviour was observed in the morphologically and ecologically closest species: the Dartford ( Sylvia undata ) and the Marmora's ( Sylvia sarda ) warblers. We did not observe any evidence of direct interspecific interactions in song, alarm, or aggressive behaviour. Nor did we observe patterns of spatial distribution that would support the idea of coexistence by interspecific territorial exclusion. These results contrast with the results of Cody & Walter (1976) suggesting interspecific territoriality in Mediterranean Sylvia warblers. They are consistent with other published results emphasizing ecological differences as explanation for species coexistence.     

Niche partitioning among three montane ground‐dwelling pheasant species along multiple ecological dimensions

Pheasants (order Galliformes) are typical ground‐dwelling birds, having a large body size and weak flight abilities. Sympatric pheasants are expected to share narrower niche space and face more extensive interspecific competition. However, little work has been undertaken simultaneously to investigate niche partitioning among sympatric pheasant species across multiple ecological dimensions. We compared microhabitat use, activity pattern and foraging strategy of sympatric Blood Pheasant Ithaginis cruentus, Buff‐throated Partridge Tetraophasis szechenyii and White Eared‐pheasant Crossoptilon crossoptilon on the Qinghai‐Tibet Plateau, China, to identify potential interspecific niche partitioning along different ecological dimensions in the breeding season. We found that the Buff‐throated Partridge differed significantly from the other two species in microhabitat use, and the three species showed different foraging strategies. It is likely that niche partitioning reduced potential interspecific competition, thus facilitating the species’ stable coexistence. Our study provides practical evidence of multidimensional niche theory within sympatric ground‐dwelling pheasant species, emphasizing that species interactions and coexistence within a guild are often not uni‐dimensional. Given global conservation concern for maintaining bird diversity, we recommend further restriction of yak grazing in these species’ habitat.     

How do similarities in spatial distributions and interspecific associations affect the coexistence of Quercus species in the Baotianman National Nature Reserve,Henan, China

Congeneric species often have similar ecological characteristics and use similar resources. These similarities may make it easier for them to co‐occur in a similar habitat but may also lead to strong competitions that limit their coexistence. Hence, how do similarities in congeneric species affect their coexistence exactly? This study mainly used spatial point pattern analysis in two 1 hm² plots in the Baotianman National Nature Reserve, Henan, China, to compare the similarities in spatial distributions and interspecific associations of Quercus species. Results revealed that Quercus species were all aggregated under the complete spatial randomness null model, and aggregations were weaker under the heterogeneous Poisson process null model in each plot. The interspecific associations of Quercus species to non‐Quercus species were very similar in Plot 1. However, they can be either positive or negative in different plots between the co‐occurring Quercus species. The spatial distributions of congeneric species, interspecific associations with non‐Quercus species, neighborhood richness around species, and species diversity were all different between the two plots. We found that congeneric species did have some similarities, and the closely related congeneric species can positive or negative associate with each other in different plots. The co‐occurring congeneric species may have different survival strategies in different habitats. On the one hand, competition among congenerics may lead to differentiation in resource utilization. On the other hand, their similar interspecific associations can strengthen their competitive ability and promote local exclusion to noncongeneric species to obtain more living space. Our results provide new knowledge for us to better understand the coexistence mechanisms of species.     

Heteromyopia and the spatial coexistence of similar competitors

Most spatial models of competing species assume symmetries in the spatial scales of dispersal and interactions. This makes analysis tractable, and has led to the conclusion that segregation of species in space does not promote coexistence. However, these symmetries leave parts of the parameter space uninvestigated. Using a moment‐approximation method, we present a spatial version of the Lotka–Volterra competition equations to investigate effects of removing symmetries in the distances over which individuals disperse and interact. Some spatial segregation of the species always comes about due to competition, and such segregation does not necessarily lead to coexistence. But, if interspecific competition occurs over shorter distances than intraspecific competition (heteromyopia), spatial segregation becomes strong enough to promote coexistence. Such coexistence is most likely when the species have similar dynamics, in contrast to the competition–colonization trade‐off that requires large competitive differences between species.     

Segregation in space and time explains the coexistence of two sympatric sub‐Antarctic petrels

Biological communities are shaped by competition between and within species. Competition is often reduced by inter‐ and intraspecific specialization on resources, such as differencet foraging areas or time, allowing similar species to coexist and potentially contributing to reproductive isolation. Here, we examine the simultaneous role of temporal and spatial foraging segregation within and between two sympatric sister species of seabirds, Northern Macronectes halli and Southern Macronectes giganteus Giant Petrels. These species show marked sexual size dimorphism and allochrony (with earlier breeding by Northern Giant Petrels) but this is the first study to test for differences in foraging behaviours and areas across the entire breeding season both between the two species and between the sexes. We tracked males and females of both species in all breeding stages at Bird Island, South Georgia, to test how foraging distribution, behaviour and habitat use vary between and within species in biological time (incubation, brood‐guard or post‐brood stages) and in absolute time (calendar date). Within each breeding stage, both species took trips of comparable duration to similar areas, but due to breeding allochrony they segregated temporally. Northern Giant Petrels had a somewhat smaller foraging range than Southern Giant Petrels, reflecting their greater exploitation of local carrion and probably contributing to their recent higher population growth. Within species, segregation was spatial, with females generally taking longer, more pelagic trips than males, although both sexes of both species showed unexpectedly plastic foraging behaviour. There was little evidence of interspecific differences in habitat use. Thus, in giant petrels, temporal segregation reduces interspecific competition and sexual segregation reduces intraspecific competition. These results demonstrate how both specialization and dynamic changes in foraging strategies at different scales underpin resource division within a community.     

Resource control by territorial male cichlid fish in Lake Malawi

1. The rocky habitat communities of Lake Malawi contain a high diversity of ecologically similar, predominantly herbivorous, cichlid fish species. How so many species can coexist is still unknown.
2. Adult males of the majority of these species hold permanent territories which form dense multispecies mosaics across the shores.
3. The study examined six coexisting species of cichlids from the rocky habitat where males are known to control access to the algal food resources within their territorial space. These included four sibling species of the Pseudotropheus ( Tropheops ) species complex, which are specialized epilithic algal herbivores, and two sibling species of the trophically more generalist P . ( Maylandia ) species complex which feed upon both epilithic algae and plankton.
4. The hypotheses that both intraspecific and interspecific territoriality occur in these communities and that interspecific aggression initiated by territorial males is preferentially directed at species with the most similar diets to their own were tested.
5. It was found that males preferred to exclude conspecific intruders, while they tolerated intruders with different diets to their own. Also, male P . ( Tropheops ) preferentially excluded similar heterospecific dietary specialists, while male P. ( Maylandia ) tolerated similar heterospecific dietary generalists.
6. Based on this study, it is proposed that interspecific territoriality may be reducing competition between species with different diets and promoting their coexistence, while it may be enhancing competition between species with the same diet. Furthermore, it suggests that ecological generalism may be reducing the intensity of interspecific competition, while specializations for the same resources may be increasing competition.     

Coupling of two competitive systems via density dependent migration

Coupling of two Lotka–Volterra type competition systems with density-dependent migration was surveyed. We assumed that species x and y are each exclusively superior in subhabitat 1 and subhabitat 2, respectively, and that population densities that exert intra-and interspecific competitive effects also impose pressures for migration of individuals from a subhabitat. If the two species are, respectively, abundant in the subhabitats in which either species is competitively superior, and the migration has a mixing effect, then, it would be intuitively expected that, as potential migration rates increase, the two species are mixed well and coexist in the whole habitat. An analysis of this competitive situation using our model under the assumption of linear diffusion predicted that, even though weak mixing maintains coexistence in the whole habitat, strong mixing collapses coexistence and leads to the exclusion of one species. The assumption that migrations occur due to self- and cross-population pressures provides different predictions: (i) weak dominance and strong mixing destabilize the coexistence state and lead to a monopolizing equilibrium of either species (bi-stability of monopolizing equiliblia); (ii) conspicuous weakness of the inferior species makes the mixing equilibrium stable, regardless of the potential migration rate; and (iii) tri-stability exists in between situations (i) and (ii). In the third case, the attainable state is the mixing equilibrium or either of the monopolizing equilibria, depending on the initial state. Migration mechanisms with self- and cross-population pressures tends to mediate spatial segregation and makes coexistence possible, even with strong mixing.     

Space invaders? A search for patterns underlying the coexistence of alien black rats and Galápagos rice rats

The introduction and spread of the black rat Rattus rattus is believed to have caused the worst decline of any vertebrate taxon in Galápagos. However, the “extinct” Santiago rice rat Nesoryzomys swarthi has recently been rediscovered in sympatry with R. rattus providing the first exception to this general pattern of displacement. We carried out an exploratory investigation of this novel system with the aim of identifying patterns that may facilitate the apparent coexistence of the two species. We carried out an extensive survey of Santiago Island to map the current distribution of the endemic rice rat and to explore broad scale distribution–habitat associations. We then used live-trapping, radio-tracking, and spool-and-line tracking to quantify abundance–habitat correlations and to test for evidence of interspecific spatial segregation, alteration of N. swarthi activity patterns (spatial and temporal), and microhabitat partitioning. We found that N. swarthi has disappeared from part of its historical range and appears to be restricted to a 14 km stretch of the north-central coast, characterised by high density of the cactus Opuntia galapageia. In contrast, the generalist R. rattus was found at all survey sites. We found no evidence of spatial segregation, and home range size, temporal activity and density of N. swarthi did not vary with local density of R. rattus. However, pre-dawn and post-dusk N. swarthi activity levels increased with R. rattus density perhaps reflecting an increase in foraging effort necessary to compensate for the costs of interspecific exploitation or interference competition. The distribution, microhabitat selection, and abundance–habitat relations of N. swarthi suggest that the endemic cactus O. galapageia may facilitate interspecific coexistence. Further research should include a comparison of inter-seasonal resource preference and foraging activity of the two species coupled with replicated field experiments to confirm and quantify competition and to elucidate the mechanism of competitive coexistence.     

Isodars unveil asymmetric effects on habitat use caused by competition between two endangered species

In order for competing species to coexist, segregation on some ecological niche component is required and is often mediated by differential habitat use. When unequal competitors are involved, the dominant species tends to displace the subordinate one to its less preferred habitat. Here, we use habitat isodars, an approach which reflects evolutionary stable strategies of habitat selection, to evaluate whether interspecific competition between two competing species with distinct habitat preferences, the little bustard Tetrax tetrax and the great bustard Otis tarda, modulates their habitat use. Field data on these endangered species demonstrate that unequal competitors can coexist without completely segregating on their preferred habitats. The negatively sloped isodar of the subordinate little bustard unveils its competition with the dominant great bustard. Interference from great bustards in secondary cereal habitats reinforces use of preferred natural habitat by little bustards. Studies of density‐dependent habitat selection by a single‐species can thus aid in identifying the effects of competition on community composition, and guide the conservation of at‐risk species. Isodars, in particular, represent a promising method to gain clear knowledge on interspecific competition for species in which experimental manipulations are not feasible.     

Environmentally and behaviourally mediated co‐occurrence of functional traits in bird communities of tropical forest fragments

Two major theories of community assembly – based on the assumption of ‘limiting similarity’ or ‘habitat filtering’, respectively – predict contrasting patterns in the spatial arrangement of functional traits. Previous analyses have made progress in testing these predictions and identifying underlying processes, but have also pointed to theoretical as well as methodological shortcomings. Here we applied a recently developed methodology for spatially explicit analysis of phylogenetic meta‐community structure to study the pattern of co‐occurrence of functional traits in Afrotropical and Neotropical bird species inhabiting forest fragments. Focusing separately on locomotory, dietary, and dispersal traits, we tested whether environmental filtering causes spatial clustering, or competition leads to spatial segregation as predicted by limiting similarity theory. We detected significant segregation of species co‐occurrences in African fragments, but not in the Neotropical ones. Interspecific competition had a higher impact on trait co‐occurrence than filter effects, yet no single functional trait was able to explain the observed degree of spatial segregation among species. Despite high regional variability spanning from spatial segregation to aggregation, we found a consistent tendency for a clustered spatial patterning of functional traits among communities in fragmented landscapes, particularly in non‐territorial species. Overall, we show that behavioural effects, such as territoriality, and environmental effects, such as the area of forest remnants or properties of the landscape matrix in which they are embedded, can strongly affect the pattern of trait co‐occurrence. Our findings suggest that trait‐based analyses of community structure should include behavioural and environmental covariates, and we here provide an appropriate method for linking functional traits, species ecology and environmental conditions to clarify the drivers underlying spatial patterns of species co‐occurrence.     

Habitat-specific estimates of competition in stream salmonids: A field test of the isodar model of habitat selection

Summary The population densities of sympatric Atlantic salmon,Salmo salar and brook charr,Salvelinus fontinalis, were measured in riffle and pool stream habitats to test whether non-linear isodars, a multispecific model of habitat selection based on ideal distribution assumptions, could (1) predict the distribution of densities between habitats and (2) reproduce the processes postulated to underlie spatial segregation and species interactions in previous laboratory and field studies. The model provided a good fit to observed density patterns and indicated that habitat suitability declined non-linearly with increased heterospecific competitor densities. Competitive effects in riffles appeared to be due to exploitative resource use, with salmon always emerging as the superior competitor. No evidence was found for interference competition in riffles. In contrast, interspecific competition in pools seemed to occur through exploitation and interference. The specific identity of the superior competitor in pools depended on the density of both species; pools provided the charr with refuge from competition with the salmon, presumably through the adoption by the charr of density-dependent behaviours, such as schooling and group foraging, that mitigated the negative impact of the salmon. Charr were displaced from the riffles toward the pools as the total salmon density increased. The isodar analysis, based on limited density data, successfully reproduced the processes suggested to underlie spatial segregation in previous field and laboratory studies and provided new insights into how changes in competitor densities modify habitat suitability in this system.     

Habitat Interference by Axis Deer on White-Tailed Deer

Abstract: Many studies of interactions between exotic and native ungulates have not had temporal and spatial controls nor have they considered the types of competitive interactions that would allow coexistence. For exotic axis deer (Axis axis) and native white-tailed deer (Odocoileus virginianus) to coexist one species should be superior at interference competition and the other species should be superior at exploitative competition. We generated and tested predictions, based on body size and diet breadth, about habitat selection by white-tailed deer in the presence and absence of axis deer, dominance relationships, and time at sites provisioned with high quality forage. We conducted our study in treatment (axis and white-tailed deer) and control (white-tailed deer only) areas when both species were present and after axis deer were removed. We conducted vehicle surveys to determine habitat use of both species. At provisioned feeding sites we recorded aggressive behaviors and amount of time species spent at feeding sites alone and together. In the treatment area white-tailed deer selection for wooded habitat increased 2.1 times after axis deer were removed, whereas habitat selection by white-tailed deer was constant in the control area over the same time. At feeding sites axis deer were dominant to white-tailed deer; both species spent a significantly greater amount of time alone than at feeders together, but amount of time that individuals of each species spent at feeders did not differ. Axis deer were superior at interference competition, but white-tailed deer were not superior at exploitative competition; thus, species coexistence is unlikely. Whether white-tailed deer are negatively impacted by axis deer at spatial scales larger than our experiment probably depends on abundance of axis deer at larger spatial scales. Experiments of species interactions with temporal and spatial controls that consider types of competitive interactions increase a manager's understanding of when and how native ungulates may be negatively impacted by exotic ungulates.     

Active dispersal is differentially affected by inter‐ and intraspecific competition in closely related nematode species

Competition is one of the main drivers of dispersal, which can be an important mechanism to achieve permanent or temporal coexistence of multiple species. This coexistence can be achieved by a dispersal‐competition tradeoff, spatial store effects or neutral dynamics. Here we test the effect of inter‐ and intraspecific competition on dispersal of four species of the marine nematode species complex Litoditis marina. A previous study in closed microcosms without a possibility for dispersal had demonstrated pronounced interspecific competition, leading to the exclusion of one species. We now investigated whether 1) the dispersal is affected by interspecific interactions, by intraspecific competition (density) or by food availability, 2) the dispersal dynamics influence assemblage composition and can lead to co‐occurrence of the species, and 3) the abiotic environment (here salinity) can affect these dynamics. We show that density is the main driver for dispersal in two of the four species. Dispersal of a third species always started at the same time irrespective of density, whereas in the fourth species interspecific interactions accelerated dispersal. Remarkably, this fourth species was not a strong competitor, suggesting that a dispersal–competition tradeoff does not explain the observed coexistence. Salinity did not alter the timing of dispersal when interspecific interactions were present but did affect assemblage composition. Consequently, spatial store effects may influence coexistence. All four species co‐occurred in fairly stable abundances throughout the present experiment indicating the importance of species specific dispersal strategies for coexistence. Co‐occurrence can be facilitated because competition is postponed or avoided by dispersal. Neutral dynamics also played a role as intra‐ and interspecific competition were of similar importance in three of the four species. We conclude that dispersal is a driver of the coexistence of closely related nematode species, and that population density and interspecific interactions shape these dynamics.     

Niche partitioning and the effect of interspecific competition on microhabitat use by two sympatric galaxiid stream fishes

1. Numerous interacting abiotic and biotic factors influence niche use and assemblage structure of freshwater fishes, but the strength of each factor changes with spatial scale. Few studies have examined the role of interspecific competition in structuring stream fish assemblages across spatial scales. We used field and laboratory approaches to examine microhabitat partitioning and the effect of interspecific competition on microhabitat use in two sympatric stream fishes (Galaxias‘southern’ and Galaxias gollumoides) at large (among streams and among sites within streams) and small (within artificial stream channels) spatial scales. 2. Diurnal microhabitat partitioning and interspecific competition at large spatial scales were analysed among three sympatry streams (streams with allotopic and syntopic sites; three separate catchments) and four allopatry streams (streams with only allotopic sites; two separate catchments). Electro‐fishing was used to sample habitat use of fishes at 30 random points within each site by quantifying four variables for each individual: water velocity, depth, distance to nearest cover and substratum size. Habitat availability was then quantified for each site by measuring those variables at each of 50 random points. Diet and stable isotope partitioning was analysed from syntopic sites only. Diel cycles of microhabitat use and interspecific competition at small spatial scales were examined by monitoring water velocity use over 48 h in artificial stream channels for three treatments: (i) allopatric G. ‘southern’ (10 G. ‘southern’); (ii) allopatric G. gollumoides (10 G. gollumoides) and (iii) sympatry (five individuals of each species). 3. One hundred and ninety‐four G. ‘southern’ and 239 G. gollumoides were sampled across all seven streams, and habitat availability between the two species was similar among all sites. Galaxias‘southern’ utilised faster water velocities than G. gollumoides in both the field and in channel experiments. Both species utilised faster water velocities in channels at night than during the day. Diet differences were observed and were supported by isotopic differences (two of three sites). No interspecific differences were observed for the other three microhabitat variables in the field, and multivariate habitat selection did not differ between species. Interspecific competition had no effect on microhabitat use of either species against any variable either in the field (large scale) or in channels (small scale). 4. The results suggest that niche partitioning occurs along a subset of microhabitat variables (water velocity use and diet). Interspecific competition does not appear to be a major biotic factor controlling microhabitat use by these sympatric taxa at any spatial scale. The results further suggest that stream fish assemblages are not primarily structured by biotic factors, reinforcing other studies de‐emphasising interspecific competition.     

Multiple routes to interspecific territoriality in sister species of North American perching birds

Behavioral interference between species can influence a wide range of ecological and evolutionary processes. Here, we test foundational hypotheses regarding the origins and maintenance of interspecific territoriality, and evaluate the role of interspecific territoriality and hybridization in shaping species distributions and transitions from parapatry to sympatry in sister species of North American perching birds (Passeriformes). We find that interspecific territoriality is pervasive among sympatric sister species pairs, and that interspecifically territorial species pairs have diverged more recently than sympatric noninterspecifically territorial pairs. None of the foundational hypotheses alone explains the observed patterns of interspecific territoriality, but our results support the idea that some cases of interspecific territoriality arise from misdirected intraspecific aggression while others are evolved responses to resource competition. The combination of interspecific territoriality and hybridization appears to be an unstable state associated with parapatry, whereas species that are interspecifically territorial and do not hybridize are able to achieve extensive fine- and coarse-scale breeding range overlap. In sum, these results suggest that interspecific territoriality has multiple origins and impacts coexistence at multiple spatial scales.     

Spatial segregation of sympatric marten and fishers: the influence of landscapes and species‐scapes

Co‐occurring species are rarely considered as a factor influencing habitat selection. However, niche theory predicts that sharing resources, predators, and other interspecific interactions can limit the environmental conditions under which a species may exist. How does the spatial distribution of one species affect that of another within shared landscapes? We tested whether sympatric marten Martes americana and fishers M. pennanti in a mountain landscape in Alberta, Canada exhibit local‐scale spatial segregation, beyond differential habitat selection. We modelled marten and fisher distribution in relation to remotely‐sensed habitat data and species co‐occurrence, using generalized linear models and information‐theoretic model selection. Marten and fishers selected different habitat types and showed different responses to habitat fragmentation. Even after accounting for these differences, the absence of one species significantly explained the occurrence of the other. We conclude that the spatial distribution of marten and fishers influences habitat selection by each other at landscape scales, and hypothesize that this pattern may result from competition in a spatially heterogeneous environment. Species‐habitat models that consider only resources may fail to capture key predictors of species’ occurrence. Reliable prediction and inference requires that ecologists expand from landscapes to also include species‐scapes: a spatial plane of species interactions that combines with resources to drive species’ distributions.     

Assessing niche partitioning of co‐occurring sibling bat species by DNA metabarcoding

Niche partitioning through foraging is a mechanism likely involved in facilitating the coexistence of ecologically similar and co‐occurring animal species by separating their use of resources. Yet, this mechanism is not well understood in flying insectivorous animals. This is particularly true of bats, where many ecologically similar or cryptic species coexist. The detailed analysis of the foraging niche in sympatric, cryptic sibling species provides an excellent framework to disentangle the role of specific niche factors likely involved in facilitating coexistence. We used DNA metabarcoding to determine the prey species consumed by a population of sympatric sibling Rhinolophus euryale and Rhinolophus mehelyi whose use of habitat in both sympatric and allopatric ranges has been well established through radio tracking. Although some subtle dietary differences exist in prey species composition, the diet of both bats greatly overlapped (O_jk = 0.83) due to the consumption of the same common and widespread moths. Those dietary differences we did detect might be related to divergences in prey availabilities among foraging habitats, which prior radio tracking on the same population showed are differentially used and selected when both species co‐occur. This minor dietary segregation in sympatry may be the result of foraging on the same prey‐types and could contribute to reduce potential competitive interactions (e.g., for prey, acoustic space). Our results highlight the need to evaluate the spatial niche dimension in mediating the co‐occurrence of similar insectivorous bat species, a niche factor likely involved in processes of bat species coexistence.     

Realised niche changes in a native herbivore assemblage associated with the presence of livestock

Habitat partitioning is a common ecological mechanism to avoid competition among coexisting species, and the introduction of new species into existing assemblages can increase competitive pressures. However, situations of species in allopatry and sympatry only differing in species presence but not in environmental conditions are scarce. Thus, discerning whether niche segregation arises from competition or from different habitat preferences is usually unfeasible. Here, we analyse species’ habitat niches in an assemblage of native and introduced herbivores in southern Patagonia. We test if niche overlap is higher between native and domestic herbivores than among natives as expected from the relatively short time of coexistence, and we evaluate the effect of intra‐ and interspecific competition on niche breadth. We use a probabilistic multidimensional approach and null models to evaluate overlap and changes in niche dimensions. Overlap among native species is low as expected for species coexisting in evolutionary time. In native‐domestic species pairs, niche overlap was higher than among natives, although showing some niche segregation indicating niche differentiation in ecological time. Moreover, the presence of domestic species was associated with niche narrowing of both native and introduced species, revealing interspecific density‐dependent effects on their habitat niche during resource shortage periods.