Are howler monkey species ecologically equivalent? Trophic niche overlap in syntopic Alouatta guariba clamitans and Alouatta caraya

According to the principle of competitive exclusion, niche differentiation allows the stable coexistence of closely related species. We analyzed dietary profile and diversity, and dietary overlap between syntopic brown howlers (BR; Alouatta guariba clamitans) and black and gold howlers (BLG; A. caraya) in the Atlantic Forest of NE Argentina, with the objective of evaluating the degree of trophic niche overlap and potential interspecific competition for food. During 12 months, we collected data on feeding behavior of two groups of each howler species using the scan sampling method, together with data on food availability. Both at the group‐ and species‐level, we analyzed feeding behavior in terms of monthly percentages of time spent feeding on each food type and specific food item, dietary diversity (Shannon index H′), and we estimated dietary overlap using the percentage index and the Morisita–Horn index (C_H). Across months, both howlers showed species‐specific preferences for certain food items, and BLG had a more diverse diet (mean±SE, H′=2.77±0.08) than BR (H′=2.39±0.09). However, diets of both species overlapped extensively (percentage index=45.64±2.97%; C_H=0.6±0.05) and diets of conspecific groups did not overlap more than diets of groups of different species. Given their high degree of trophic overlap, syntopic BR and BLG meet one of the conditions necessary for interspecific food competition to occur. Although at present we lack direct evidence for interspecific competition in these howler species, we conclude that high levels of niche overlap may have an important role in maintaining the essentially parapatric distribution of howler species throughout the Neotropics. Am. J. Primatol. 72:173–186, 2010. © 2009 Wiley‐Liss, Inc.     

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.     

Ecological niche differences betweenAlouatta palliata andCebus capucinus comparing feeding modes,branch use,and diet

During the wet season, two sympatric species of primates,Alouatta palliata (mantled howlers) andCebus capucinus (white-faced capuchins), were assayed for feeding niche differences through behavioral and habitat use patterns at Refugio de Fauna Silvestre Curu in Costa Rica. Differences in the use of relative diameter and thickness of branches and five different modes of feeding were compared between the species. White-faced capuchins used more manipulative modes of obtaining food, a wider range of arboreal habitat, and had a more diverse diet than mantled howlers. Mantled howlers may be more restricted than white-faced capuchins in arboreal microhabitat use due to their possible need for large support branches during feeding bouts and resting periods. We report that differences in feeding behaviors, diet, and arboreal habitat use seem to play a large role in separating these species niches.     

Resource partitioning and interspecific competition in snakes: the search for general geographical and guild patterns

The role of interspecific competition as a key factor in the ecology of natural communities where species exploit limited resources is well established, and the study of competition dynamics in snake communities has received much attention in recent years. Twenty years ago, an acclaimed review ( Toft 1985 ) suggested that snakes were atypical among vertebrates because sympatric species usually partition the food niche. Here, I review the articles published in the last two decades with the aim of finding any general geographical or guild patterns and assessing if Toft's main conclusion is still supported by new evidence. Where appropriate, I use Monte Carlo simulations to establish whether observed patterns of niche overlap are real, or if they have occurred by chance. My study shows clear congruence in the patterns of coexistence exhibited by snake communities in different regions of the world, i.e.: (1) cold regions of the northern hemisphere (high latitudes and altitudes) exhibit low species richness and a very low, or even absent, potential for interspecific competition; (2) aquatic snakes that form communities in temperate regions generally partition the food type available and exhibit a broad similarity in habitat use with subtle differences in microhabitat use; (3) terrestrial snake communities in temperate regions are very variable in terms of their coexistence dynamics and show no evidence of generalised patterns; (4) sympatric viperids in Europe, North America and, most interestingly, tropical Asia partition the available habitat but not the prey resource; (5) competition is much stronger in tropical snake communities, and the intensity of this process fluctuates throughout the year being most intense during periods of low food availability; (6) in general, tropical snakes partition the food resource (prey type and/or prey size), but when this resource is not partitioned competitive exclusion can occur. Prey resource availability is a fundamental variable for all snake communities; this is clearly documented by studies on terrestrial snakes in Australia where, due to a relative scarcity of prey availability in the field, sympatry among species is much rarer than in other continents. I conclude that, although there are several notable exceptions, Toft's main conclusion is still supported by empirical evidence. However, I disagree with Toft's conclusion that most snakes are food specialists, and I contend that interspecific competition is important in structuring many (if not most) of the snake communities around the world.     

Diet and activity pattern of howler monkeys (Alouatta palliata) in Los Tuxtlas, Mexico: effects of habitat fragmentation and implications for conservation

Accelerated deforestation is causing the rapid loss and fragmentation of primary habitat for primates. Although the genus Alouatta is one of the most studied primate taxa under these circumstances, some results are contradictory and responses of howlers to habitat fragmentation are not yet clear. In this paper, we conduct a cross-study of the available researches on mantled howlers (Alouatta palliata) in forest fragments in Los Tuxtlas, Mexico, to (1) describe the diet and activity pattern of howlers; (2) analyze the similarity in the diet across studies; and (3) relate both fragment size and howler population density with different characteristics of their diet, home range size, and activity pattern. Howlers consumed 181 plant species belonging to 54 families. Ficus was the most important taxa in the howlers' diet, followed by primary species such as Pterocarpus rohrii, Nectandra ambigens, Poulsenia armata, and Brosimum alicastrum. Secondary and non-secondary light-demanding plant species, which are representatives of disturbed habitat, contributed with a high percentage of their feeding time. Only 23% of the species consumed were the same across all the studies, suggesting that howlers adapt their diet to the food availability of their respective habitats. Population density is the best predictor of howlers' ecological and behavioral changes in response to forest fragmentation, probably owing to its relationship with food availability. Howlers respond to the increase in population densities by increasing the (1) diversity of food species in the diet; (2) consumption of non-tree growth forms; and (3) consumption of new plant items. Home range size is also predicted by population density, but fragment size is a better predictor, probably owing to the fact that howler groups can overlap their home ranges. Our results emphasize the importance of conserving the larger fragments and increasing the size of small and medium-sized ones.     

Habitat selection and seasonal patterns of activity and foraging of mantled howling monkeys(Alouatta Palliata) in Northeastern Costa Rica

I conducted a 15- month ecological study of habitat preferences and activity and foraging patterns of two troops of mantled howling monkeys, Alouatta palliata,in a lowland rain forest at La Selva Biological Reserve in northeastern Costa Rica. The two troops specialized on different habitats in spite of the fact that both of them had all habitats available and were not constrained by neighboring troops since the population density of howlers is low (7- 15 howlers/km ² ).Troop 1 spent the majority of time in primary forest (80%) followed by secondary forest (10%), while troop 2 spent the majority of time in undisturbed riparian habitat (60%) followed by primary forest (30%). Habitat sampling indicates that neither the total number of stems, species, or families nor the diversity (Shannon index) or evenness is a good indicator for howler habitat selection. Instead the density of trees from the 12 species most commonly consumed by each troop is the most important factor. Activity and foraging patterns were not dependent upon the season as has been described for howling monkeys in forests with a more pronounced dry season at Barro Colorado Island, Panama, and La Pacifica in northwestern Costa Rica. This is likely a result of the more constant food supply at La Selva, combined with less intraspecific competition due to the low howler density. The intraspecific variability of foraging patterns and troop- specific habitat specialization observed in Alouatta palliatashould be considered in the conservation biology of primates. Primate relocation programs should include not only an ecological assessment of the release site but also a comparison of the release site with the habitat that the groups currently occupy.     

Seasonal Changes in Feeding Ecology and Activity Patterns of Two Sympatric Mouse Lemur Species,the Gray Mouse Lemur (<Emphasis Type="Italic">Microcebus murinus</Emphasis>) and the Golden-brown Mouse Lemur (<Emphasis Type="Italic">M. ravelobensis</Emphasis>), in Northwestern Madagascar

Because closely related species are likely to be ecologically similar owing to common ancestry, they should show some degree of differentiation in order to coexist. We studied 2 morphologically similar congeneric species, the golden-brown mouse lemur (Microcebus ravelobensis) and the gray mouse lemur (M. murinus). These species are found in partial sympatry in the dry deciduous forest in northwestern Madagascar. We investigated whether 1) feeding niche differentiation and/or 2) a reduction in locomotor activity during periods of food shortage, which might reflect an energy saving strategy, can explain the coexistence of these 2 lemur species. To obtain feeding and behavioral data, we conducted focal observations of 11 female Microcebus murinus and 9 female M. ravelobensis during 11 months from 2007 to 2008 and collected fecal samples for 6 mo. We monitored the phenology of 272 plant specimens and trapped arthropods to determine food availability. Results revealed interspecific differences in 1) relative proportion of consumed food resources, resulting in a merely partial dietary overlap, and in 2) relative importance of seasonally varying food resources throughout the year. In addition, females of Microcebus murinus showed a reduction in locomotor activity during the early dry season, which might reflect an energy-saving strategy and might further reduce potential competition with M. ravelobensis over limited food resources. To conclude, a combination of interspecific feeding niche differentiation and differences in locomotor activity appears to facilitate the coexistence of Microcebus murinus and M. ravelobensis.     

Space Use Variation in Co-Occurring Sister Species: Response to Environmental Variation or Competition?

Coexistence often involves niche differentiation either as the result of environmental divergence, or in response to competition. Disentangling the causes of such divergence requires that environmental variation across space is taken into account, which is rarely done in empirical studies. We address the role of environmental variation versus competition in coexistence between two rodent species: Rhabdomys bechuanae (bechuanae) and Rhabdomys dilectus dilectus (dilectus) comparing their habitat preference and home range (HR) size in areas with similar climates, where their distributions abut (allopatry) or overlap (sympatry). Using Outlying Mean Index analyses, we test whether habitat characteristics of the species deviate significantly from a random sample of available habitats. In allopatry, results suggest habitat selection: dilectus preferring grasslands with little bare soil while bechuanae occurring in open shrublands. In sympatry, shrubland type habitats dominate and differences are less marked, yet dilectus selects habitats with more cover than bechuanae. Interestingly, bechuanae shows larger HRs than dilectus, and both species display larger HRs in sympatry. Further, HR overlaps between species are lower than expected. We discuss our results in light of data on the phylogeography of the genus and propose that evolution in allopatry resulted in adaptation leading to different habitat preferences, even at their distribution margins, a divergence expected to facilitate coexistence. However, since sympatry occurs in sites where environmental characteristics do not allow complete species separation, competition may explain reduced inter-species overlap and character displacement in HR size. This study reveals that both environmental variation and competition may shape species coexistence.     

Interspecific competition promotes habitat and morphological divergence in a secondary contact zone between two hybridizing songbirds

Interspecific competition is assumed to play an important role in the ecological differentiation of species and speciation. However, empirical evidence for competition's role in speciation remains surprisingly scarce. Here, we studied the role of interspecific competition in the ecological differentiation and speciation of two closely related songbird species, the Common Nightingale (Luscinia megarhynchos) and the Thrush Nightingale (Luscinia luscinia). Both species are insectivorous and ecologically very similar. They hybridize in a secondary contact zone, which is a mosaic of sites where both species co‐occur (syntopy) and sites where only one species is present (allotopy). We analysed fine‐scale habitat data for both species in both syntopic and allotopic sites and looked for associations between habitat use and bill morphology, which have been previously shown to be more divergent in sympatry than in allopatry. We found that the two nightingale species differ in habitat use in allotopic sites, where L. megarhynchos occurred in drier habitats and at slightly higher elevations, but not in syntopic sites. Birds from allotopic sites also showed higher interspecific divergence in relative bill size compared to birds from syntopic sites. Finally, we found an association between bill morphology and elevation. Our results are consistent with the view that interspecific competition in nightingales has resulted in partial habitat segregation in sympatry and that the habitat‐specific food supply has in turn very likely led to bill size divergence. Such ecological divergence may enhance prezygotic as well as extrinsic postzygotic isolation and thus accelerate the completion of the speciation process.     

Prey use of wetland benthivorous sunfishes: ontogenetic, interspecific and seasonal variation

The intensity of competitive interactions between fishes is partly determined by prey use and ontogenetic niche shifts. In a wetland where distinct habitat shifts are missing we compared prey use of three generalist benthivorous sunfishes to look for evidence of ontogenetic, interspecific, and “seasonal” variation in prey composition. Diet analysis revealed evidence of diet ontogeny in warmouth (Lepomis gulosus, 30–152 mm standard length, SL), but not in bluespotted sunfish (Enneacanthus gloriosus, 30–47 mm SL) or dollar sunfish (Lepomis marginatus, 30–60 mm SL). Bluespotted and dollar sunfishes consumed small dipteran and amphipod prey and had similar diets in both seasons suggesting a potential for strong interspecific competition. In the dry season, warmouth shifted from using smaller insect prey to larger decapod and fish prey with increasing size. This shift to prey types that were little used by the other species reduced dietary niche overlap with the other sunfishes. After drought and re-flooding (in the wet season), decapods and small fish were less abundant in the wetland and the warmouth ontogenetic shift was less distinct. When matched for gape width, prey composition differed between warmouth and both dollar and bluespotted sunfishes in the wet season, suggesting differences in sunfish foraging modes, but prey use differences were less clear in the dry season when prey were abundant. Both warmouth ontogenetic diet shifts and seasonal variation in prey use (probably mediated by prey abundance) had strong influences on diet overlap and therefore the potential for intra- and interspecific competition between sunfishes in this wetland ecosystem.     

Darwin's finches and their diet niches: the sympatric coexistence of imperfect generalists

Adaptive radiation can be strongly influenced by interspecific competition for resources, which can lead to diverse outcomes ranging from competitive exclusion to character displacement. In each case, sympatric species are expected to evolve into distinct ecological niches, such as different food types, yet this expectation is not always met when such species are examined in nature. The most common hypotheses to account for the coexistence of species with substantial diet overlap rest on temporal variation in niches (often diets). Yet spatial variation in niche overlap might also be important, pointing to the need for spatiotemporal analyses of diet and diet overlap between closely related species persisting in sympatry. We here perform such an analysis by characterizing the diets of, and diet overlap among, four sympatric Darwin's ground finch species at three sites and over 5 years on a single Galápagos island (Santa Cruz). We find that the different species have broadly similar and overlapping diets – they are to some extent generalists and opportunists – yet we also find that each species retains some ‘private’ resources for which their morphologies are best suited. Importantly, use of these private resources increased considerably, and diet overlap decreased accordingly, when the availability of preferred shared foods, such as arthropods, was reduced during drought conditions. Spatial variation in food resources was also important. These results together suggest that the ground finches are ‘imperfect generalists’ that use overlapping resources under benign conditions (in space or time), but then retreat to resources for which they are best adapted during periods of food limitation. These conditions likely promote local and regional coexistence.     

Primates Living Outside Protected Habitats Are More Stressed: The Case of Black Howler Monkeys in the Yucatán Peninsula

The non-invasive monitoring of glucocorticoid hormones allows for the assessment of the physiological effects of anthropogenic disturbances on wildlife. Variation in glucocorticoid levels of the same species between protected and unprotect areas seldom has been measured, and the available evidence suggests that this relationship may depend on species-specific habitat requirements and biology. In the present study we focused on black howler monkeys (Alouatta pigra), a canopy-dwelling primate species, as a case study to evaluate the physiological consequences of living in unprotected areas, and relate them with intragroup competition and competition with extragroup individuals. From February 2006 to September 2007 we collected 371 fecal samples from 21 adults belonging to five groups (two from protected and three from unprotected areas) in Campeche, Mexico. We recorded agonistic interactions within groups and encounters with other groups (1,200 h of behavioral observations), and determined fecal glucocorticoid metabolite (FGM) concentrations with radioimmunoassays. We used linear mixed models and Akaike''s information criterion to choose the best model explaining variation in FGM concentrations between protected and unprotected areas calculated from five categorical variables: habitat type (protected vs. unprotected), participation in agonistic interactions, intergroup encounters, sex and female reproductive state, and season. The best model included habitat type, the interaction between habitat type and agonism, and the interaction between habitat type and season. FGM concentrations were higher in unprotected habitats, particularly when individuals were involved in agonistic interactions; seasonal variation in FGM concentrations was only detected in protected habitats. High FGM concentrations in black howler monkeys living in unprotected habitats are associated with increased within-group food competition and probably associated with exposure to anthropogenic stressors and overall food scarcity. Because persistent high GC levels can be detrimental to health and fitness, populations living in disturbed unprotected areas may not be viable in the long-term.     

Effect of habitat degradation on competition,carrying capacity,and species assemblage stability

Changes in species’ trophic niches due to habitat degradation can affect intra‐ and interspecific competition, with implications for biodiversity persistence. Difficulties of measuring species’ interactions in the field limit our comprehension of competition outcomes along disturbance gradients. Thus, information on how habitat degradation can destabilize food webs is scarce, hindering predictions regarding responses of multispecies systems to environmental changes. Seagrass ecosystems are undergoing degradation. We address effects of Posidonia oceanica coverage reduction on the trophic organization of a macroinvertebrate community in the Tyrrhenian Sea (Italy), hypothesizing increased trophic generalism, niche overlap among species and thus competition and decreased community stability due to degraded conditions. Census data, isotopic analysis, and Bayesian mixing models were used to quantify the trophic niches of three abundant invertebrate species, and intra‐ and interspecific isotopic and resource‐use similarity across locations differing in seagrass coverage. This allowed the computation of (1) competition strength, with respect to each other and remaining less abundant species and (2) habitat carrying capacity. To explore effects of the spatial scale on the interactions, we considered both individual locations and the entire study area (“‘meadow scale”). We observed that community stability and habitat carrying capacity decreased as P. oceanica coverage declined, whereas niche width, similarity of resource use and interspecific competition strength between species increased. Competition was stronger, and stability lower, at the meadow scale than at the location scale. Indirect effects of competition and the spatial compartmentalization of species interactions increased stability. Results emphasized the importance of trophic niche modifications for understanding effects of habitat loss on biodiversity persistence. Calculation of competition coefficients based on isotopic distances is a promising tool for describing competitive interactions in real communities, potentially extendible to any subset of ecological niche axes for which specimens’ positions and pairwise distances can be obtained.     

Competing for crevices: interspecific conflict influences retreat-site selection in montane lizards

Direct interference competition between sympatric taxa affects habitat use and shelter-site selection in species within most major vertebrate lineages. However, studies on interspecific social interference in reptiles largely have been confined to research on interactions between non-native (invasive) species and native fauna. Does interspecific interference also influence habitat use within natural assemblages of reptiles? We studied five broadly sympatric species of viviparous montane skinks within the genera Egernia and Eulamprus in southeastern Australia. Previous work has shown strong interspecific overlap in abiotic attributes of shelter-sites for these taxa, but no joint occupancy of retreats. Laboratory trials in which we manipulated the identity of co-occurring lizards revealed frequent displacement from “preferred” (hotter) shelters, with interspecific interactions more intense than intraspecific conflicts. The five species displayed a linear interspecific dominance hierarchy, with larger species displacing smaller taxa. Field manipulations confirmed that interspecific interactions between these species affect shelter-site use. We conclude that direct agonistic encounters between individuals of different species strongly influence habitat use by lizards within this assemblage.     

Intraspecific and interspecific competition induces density‐dependent habitat niche shifts in an endangered steppe bird

Interspecific competition is a dominant force in animal communities that induces niche shifts in ecological and evolutionary time. If competition occurs, niche expansion can be expected when the competitor disappears because resources previously inaccessible due to competitive constraints can then be exploited (i.e., ecological release). Here, we aimed to determine the potential effects of interspecific competition between the little bustard (Tetrax tetrax) and the great bustard (Otis tarda) using a multidimensional niche approach with habitat distribution data. We explored whether the degree of niche overlap between the species was a density‐dependent function of interspecific competition. We then looked for evidences of ecological release by comparing measures of niche breadth and position of the little bustard between allopatric and sympatric situations. Furthermore, we evaluated whether niche shifts could depend not only on the presence of great bustard but also on the density of little and great bustards. The habitat niches of these bustard species partially overlapped when co‐occurring, but we found no relationship between degree of overlap and great bustard density. In the presence of the competitor, little bustard's niche was displaced toward increased use of the species' primary habitat. Little bustard's niche breadth decreased proportionally with great bustard density in sympatric sites, in consistence with theory. Overall, our results suggest that density‐dependent variation in little bustard's niche is the outcome of interspecific competition with the great bustard. The use of computational tools like kernel density estimators to obtain multidimensional niches should bring novel insights on how species' ecological niches behave under the effects of interspecific competition in ecological communities.     

Effects of habitat fragmentation and disturbance on howler monkeys: a review

We examined the literature on the effects of habitat fragmentation and disturbance on howler monkeys (genus Alouatta) to (1) identify different threats that may affect howlers in fragmented landscapes; (2) review specific predictions developed in fragmentation theory and (3) identify the empirical evidence supporting these predictions. Although howlers are known for their ability to persist in both conserved and disturbed conditions, we found evidence that they are negatively affected by high levels of habitat loss, fragmentation and degradation. Patch size appears to be the main factor constraining populations in fragmented habitats, probably because patch size is positively related to food availability, and negatively related to anthropogenic pressures, physiological stress and parasite loads. Patch isolation is not a strong predictor of either patch occupancy or population size in howlers, a result that may be related to the ability of howlers to move among forest patches. Thus, we propose that it is probable that habitat loss has larger consistent negative effects on howler populations than habitat fragmentation per se. In general, food availability decreases with patch size, not only due to habitat loss, but also because the density of big trees, plant species richness and howlers' home range size are lower in smaller patches, where howlers' population densities are commonly higher. However, it is unclear which vegetation attributes have the biggest influence on howler populations. Similarly, our knowledge is still limited concerning the effects of postfragmentation threats (e.g. hunting and logging) on howlers living in forest patches, and how several endogenous threats (e.g. genetic diversity, physiological stress, and parasitism) affect the distribution, population structure and persistence of howlers. More long‐term studies with comparable methods are necessary to quantify some of the patterns discussed in this review, and determine through meta‐analyses whether there are significant inter‐specific differences in species' responses to habitat loss and fragmentation. Am. J. Primatol. 72:1–16, 2010. © 2009 Wiley‐Liss, Inc.     

Effective Solutions for Howler Conservation

All species of howlers are at risk due to habitat destruction. I review the three most serious threats to howler survival—agricultural disturbance, logging disturbance, and hunting—both in a general context and in species accounts. Withal, the adaptability of howlers has allowed them to be a widespread genus throughout Central and South America. Alouatta is especially adaptable due to its generalized folivorous diet. I discuss how this adaptability relates to survival in situations of habitat destruction. In addition, I examine howler preference for riverine habitats and their ability to capitalize on secondary forests and secondary growth. I take a practical approach, suggesting some solutions for species survival, which include habitat management and reintroductions. Successful conservation models highlighted are the Community Baboon Sanctuary in Belize, in which villagers manage their lands for the benefit of the black howler and for their own economic benefit from ecotourism, and a village-sustainable logging system in Quintana Roo, Mexico, which has reduced levels of deforestation while benefiting both villagers and howlers, as well as other wildlife. A successful translocation of black howlers in Belize in order to reestablish a viable population is also described. The paper concludes with further suggestions to encourage howler conservation.     

Habitat displacement effect between two competing owl species in fragmented forests

Many owl species use the same nesting and food resources, which causes strong interspecific competition and spatio-temporal niche separation. We made use of a recent colonisation of Ural Owls (Strix uralensis) in southern Poland to compare habitat preferences of Tawny Owls (Strix aluco) allopatry and sympatry with Ural Owls. We investigated spatial niche segregation of Ural Owl and the Tawny Owl in sympatry and compared habitat preferences of Tawny Owls breeding in allopatry and sympatry. Tawny Owls breeding in sympatry with Ural Owls occupied forests with higher canopy compactness, sites located closer to forest border and to built-up areas, as well as stands with a higher share of fir and spruce and a lower share of beech as compared to sites occupied by Ural Owls. Allopatric Tawny Owls occupied sites with lower canopy compactness and bred at sites located further from forest borders and in stands with lower share of fir and spruce and a higher share of deciduous as compared to sympatric Tawny Owls. As Ural owls are dominant in relation to Tawny Owls, this indicates that the presence of Ural Owls prevents Tawny Owls from occupying deciduous-dominated and old stands located in forest interior areas, far from buildings and forest edges. The results support habitat displacement between the two species when breeding in sympatry. We also show that protection of large forest patches is crucial for the Ural Owl, a species still rare in central Europe, while small patches are occupied by the abundant Tawny Owl.     

Roles of endothermy in niche differentiation for ball-rolling dung beetles (Coleoptera: Scarabaeidae) along an altitudinal gradient

Abstract.  1. An analysis of whether niche differentiation in ball-rolling dung beetles can be explained by the way in which they regulate their body temperature was conducted.
2.  A priori assumptions were: (i) if thermoregulation affects niche partitioning, sympatric species must have different endothermic strategies that minimise encounters; or, alternatively (ii) if two co-occurring species show the same thermoregulation pattern and their flight periods overlap, they might be avoiding competition by exhibiting different resource preferences or different food relocation behaviour.
3. The ball-rolling dung beetles studied showed a hierarchical structure based on the species' endothermic capacity, measured as temperature excess [ T _ex= difference between body temperature ( T _b) and ambient temperature ( T _a)]. Those with a high T _ex (10–15 °C) were located exclusively at altitudes >1000 m a.s.l. On the coastal plains, species with a high T _ex were restricted to flying at night when the T _a was lower. Species with a lower T _ex (less than 10 °C higher than T _a) were found in the coastal plains zone.
4. Where there was sympatry with similar trophic habits, the species involved showed very different thermal niches, and where there was significant overlap of thermal niches between sympatric species, trophic habits of species were very different.
5. The results suggest that it is possible to use the concept of the thermal niche as a tool to explain interspecific interactions and the spatial distribution of species.