Predation risk alters interactions among species: competition and facilitation between ants and nesting birds in a boreal forest

Although interactions between species are often assumed to be fixed, theory and empirical evidence suggest that they may be quite variable, changing in the presence of other species or environmental conditions. The interaction between ants and nesting birds exhibits such variability, ants sometimes being predators of bird nests and other times protectors of them. Hypothesizing that predation risk might be a critical factor in altering the interaction of ants with birds, I investigated the interaction of wood ants Formica aquilonia with nesting birds under different levels of predation risk. In a controlled field experiment, I allowed tits ( Parus major, P. caeruleus, P. ater ) and pied flycatchers ( Ficedula hypoleuca ) to select nest boxes in trees with ants (ant trees) or trees without ants. I found that birds usually nested in trees without ants, apparently to avoid the danger of injury from encounters with ants. Nesting in ant trees occurred mainly in the habitat where risk of predation was highest (along the forest edge), and with the bird taxa that lost nests most frequently in trees without ants (tits). Tits nesting on the forest edge achieved significantly greater nesting success, and fledged significantly more young, in ant trees compared with trees without ants. As the season progressed, ant traffic increased in trees without nesting birds, but decreased in trees with nesting birds, indicating that the outcome of interference competition between ants and nesting birds was reversed under increased predation risk. These results support the idea that predation risk can shift species interactions from predominately competitive processes to predominately facilitative processes.     

Dispersal and the interspecific abundance-occupancy relationship in British birds

Aim To test the prediction that deviations of species from the positive interspecific relationship between abundance and occupancy (a measure of geographical range size) are related to differences in dispersal. Location Great Britain. Methods Quantitative data on the abundances, occupancy and dispersal distances of British birds are compared using phylogenetic comparative methods. Results Measures of natal and adult dispersal distance, and the intraspecific variance in these parameters, explain little variation in occupancy in addition to that accounted for by population size. Individual dispersal variables failed to explain significant variance when added individually to a model with population size as a predictor. Migrants and species using wet habitats tend to disperse further than residents and dry habitat species. Analysing these four groups separately revealed effects of dispersal only on the occupancy attained by dry habitat species. Conclusions The only consistent predictor of occupancy in these analyses was population size.     

Ecological and evolutionary consequences of selective interspecific information use

Recent work has shown that animals frequently use social information from individuals of their own species as well as from other species; however, the ecological and evolutionary consequences of this social information use remain poorly understood. Additionally, information users may be selective in their social information use, deciding from whom and how to use information, but this has been overlooked in an interspecific context. In particular, the intentional decision to reject a behaviour observed via social information has received less attention, although recent work has indicated its presence in various taxa. Based on existing literature, we explore in which circumstances selective interspecific information use may lead to different ecological and coevolutionary outcomes between two species, such as explaining observed co-occurrences of putative competitors. The initial ecological differences and the balance between the costs of competition and the benefits of social information use potentially determine whether selection may lead to trait divergence, convergence or coevolutionary arms race between two species. We propose that selective social information use, including adoption and rejection of behaviours, may have far-reaching fitness consequences, potentially leading to community-level eco-evolutionary outcomes. We argue that these consequences of selective interspecific information use may be much more widespread than has thus far been considered.     

利用天然树洞繁殖的五种鸟的巢位特征及繁殖成功率

对吉林省左家自然保护区次生阔叶林中的大山雀 ( Parusmajor)、沼泽山雀 ( Paruspalustris)、普通跓( Sitta europacea)、白眉姬? ( Ficedula zanthopygia)和灰椋鸟 ( Sturnus cineraceus) 5种利用天然树洞繁殖的次级洞巢鸟进行了巢位选择和繁殖成功率研究。本研究中共发现 1 41巢。五种鸟对树洞类型的选择存在种间差异 ,普通跓不利用裂洞 ,沼泽山雀不利用啄洞 ,其它 3种鸟对 3种洞均有利用 ,但有一定的倾向性。对 5种鸟 9个巢位变量的比较中 ,只有洞口方向差异不显著 ( p >0 .0 5 ) ,其它 8个变量均差异显著 ( p<0 .0 5 ) ,该结果说明 5种次级洞巢鸟对巢位的选择具有其各自的需求。洞口横径、洞口纵径、洞处树直径、洞内径、巢距地高是巢位选择重要变量 ,它们决定不同种类对树洞的利用。巢损失多数出现在产卵之前和孵化阶段 ,44个繁殖失败的巢中有 35个在这两个阶段损失。大山雀的巢成功率最低 ,灰椋鸟的巢成功率最高。 5种鸟的孵化率都超过 90 %。人为破坏和动物捕食是繁殖失败的主要原因 ,占总数的 61 .4%。洞巢鸟巢位选择中的重要变量影响繁殖成功。普通跓繁殖是否成功受洞口横径和巢高影响 ,沼泽山雀受洞口纵径、树胸径和洞内径影响 ,大山雀受洞口横径、巢高和洞内径影响 ,灰椋鸟受洞内径和洞深影     

Habitat characteristics and species interference influence space use and nest‐site occupancy: implications for social variation in two sister species

Nest‐site selection is an important component of species socio‐ecology, being a crucial factor in establishment of group living. Consequently, nest‐site characteristics together with space‐use proxies may reveal the social organization of species, which is critical when direct observation of social interactions is hindered in nature. Importantly, nest‐site choice is expected to be under strong selective pressures and the object of intra‐ and interspecific competition. Although the bulk of research on sociality focuses on its ecological drivers, our study introduces interspecific competition as a potential factor that could influence social evolution. We investigated the influence of habitat and interspecific competition on the social organization of two sister species of the African four striped mouse, Rhabdomys dilectus dilectus and Rhabdomys bechuanae, in a similar macroenvironment. These species diverged in allopatry and occupy distinct environmental niches. We radiotracked 140 adults to identify their nest‐sites, determine nest characteristics and record groups that shared nest‐sites. Group cohesion was estimated from nest‐site fidelity, group association strength, and home range overlap within versus between group members. We compared the two species in sympatry versus parapatry to determine the impact of species interference on sociality. In parapatry, the two species selected distinct nest‐site types, interpreted as different anti‐predator strategies: R. bechuanae selected fewer, spaced, less concealed nest‐sites whereas R. d. dilectus selected clumped and less visible nest‐sites. Rhabdomys bechuanae also showed more cohesive and stable social groups than R. d. dilectus. In sympatry, compared to R. bechuanae, R. d. dilectus occupied similar nest‐sites, however slightly more exposed and clumped, and displayed similar nest‐site fidelity and group association strength. We conclude that although habitat selection may be an important driver of social divergence in Rhabdomys, species interference, by limiting R. d. dilectus movements and forcing nest‐site sharing may induce new ecological pressures that could influence its social evolution.     

Habitat use,abundance, and persistence of Neotropical migrant birds in a habitat matrix in northeast Belize

ABSTRACT To ensure adequate protection of nonbreeding habitats used by Neotropical migratory landbirds, we must first address questions about habitat use and quality. On the Yucatan peninsula, migrants use many habitats, several of which remain unstudied, and methodological differences preclude interhabitat comparisons based on studies to date. We used distance sampling along line transects in six habitats in northeast Belize to examine use of previously unstudied habitats (e.g., salt marsh) by Neotropical migrants and to permit comparison across habitats. We calculated unadjusted and adjusted (for detectability) density estimates for individual migrant species and for all species combined to generate hypotheses about habitat quality based on the assumption that density and quality are positively correlated. Adjusted density estimates for all migrants were highest in black mangrove habitat (1799 ± 110 ind/km²), intermediate in three forest types and milpa (range 598–802 ind/km²), and lowest in salt marsh (207 ± 32.3 ind/km²). By combining density estimates with habitat availability in our study region, we estimated that evergreen forest and black mangrove supported 70% and 9% of the region's migrant population, respectively. At the species level, five of the 10 most common species had habitat preferences (>50% detections in one habitat). Given the diversity of habitat preferences among species and apparent seasonal movements, our results indicate that Neotropical migrants in northeast Belize are dependent on a matrix of interconnected habitats.     

Impacts of passage migrant songbirds on behaviour and habitat use of resident Sardinian Warblers Sylvia melanocephala in Gibraltar

Explanations for the coexistence of migratory and sedentary (resident) birds are much debated: some authors have suggested that migrants make use of surplus resources not exploited by residents, whereas others have recorded ecological shifts in residents during periods when migrants are present. These shifts have been ascribed to the presence of migrants but could equally reflect seasonal variation in the distribution of resources required by sedentary species. Here we assess how the abundance of migrants affects the territorial behaviour and habitat use of resident Sardinian Warblers Sylvia melanocephala at a stop‐over site on the Rock of Gibraltar. There was a significant positive relationship between the abundance of migrants and the distances moved, time spent calling and the species and functional diversity of plants used by Sardinian Warblers on a daily basis, suggesting that migrants have a significant impact on residents.     

Effects of elevated CO2 on the interspecific competition between two sympatric species of Aphis gossypii and Bemisia tabaci fed on transgenic Bt cotton

Abstract Effects of elevated CO₂ (twice ambient vs. ambient) and Bt Cry1Ac transgene (Bt cotton cv. 33^B vs. its nontransgenic parental line cv. DP5415) on the interspecific competition between two ecologically similar species of cotton aphid Aphis gossypii and whitefly biotype‐Q Bemisia tabaci were studied in open‐top chambers. The results indicated that elevated CO₂ and Bt cotton both affected the population abundances of A. gossypii and biotype‐Q B. tabaci when introduced solely (i.e., without interspecific competition) or two species coexisted (i.e., with interspecific competition). Compared with ambient CO₂, elevated CO₂ increased the population abundances of A. gossypii and biotype‐Q B. tabaci as fed on Bt and nontransgenic cotton on 45 (i.e., seedling stage) and 60 (i.e., flowering stage) days after planting (DAP), but only significantly enhanced aphid abundance without interspecific competition on the 45‐DAP nontransgenic cotton and 60‐DAP Bt cotton, and significantly increased whitefly abundance with interspecific competition on the 45‐DAP Bt cotton and 60‐DAP nontransgenic cotton. In addition, compared with nontransgenic cotton at elevated CO₂, Bt cotton significantly reduced biotype‐Q B. tabaci abundances without and with interspecific competition during seedling and flowering stage, while only significantly decreasing A. gossypii abundances without interspecific competition during the seedling stage. When the two insect species coexisted, the proportions of biotype‐Q B. tabaci were significantly higher than those of A. gossypii on Bt and nontransgenic cotton at the same CO₂ levels, and elevated CO₂ only significantly increased the percentages of biotype‐Q B. tabaci and significantly reduced the proportions of A. gossypii on seedling and flowering nontransgenic cotton. Therefore, the effects of elevated CO₂ were favorable for biotype‐Q B. tabaci to out‐compete A. gossypii under the predicted global climate change.     

Shoal and prey patch choice by co-occurring fishes and prawns: inter-taxa use of socially transmitted cues

Animals can use socially transmitted information to learn about the distribution and quality of resources without incurring the costs associated with having to search for and sample them first hand. Recently, it has been shown that the use of chemical social information specific to patterns of diet and habitat use is an important mechanism underpinning recognition and social organization in shoaling fishes. In this study we revealed that the use of resource-specific chemical information is not limited to conspecifics, or even members of the same taxon. In a series of laboratory experiments, we showed that threespine sticklebacks (Gasterosteus aculeatus) could recognize similar patterns of habitat use in common prawns (Leander serratus), preferentially orientating towards groups of prawns exposed to the same habitats as themselves, and even selecting foraging patches located close to them. Prawns were seen to use habitat-specific cues generated by conspecifics, but not by sticklebacks, suggesting that the benefits of forming these heterospecific social association patterns may be unequal for prawns and fishes. Our findings suggest that some species might use co-occurring, unrelated species as information centres in order to orient and locate resources within their surroundings.     

When carnivores collide: a review of studies exploring the competitive interactions between bobcats Lynx rufus and coyotes Canis latrans

1. Bobcats Lynx rufus and coyotes Canis latrans are two widespread mesopredators with a complex history of sympatry. The competitive interactions between these species are of interest to biologists due to the furbearer status of bobcats, the recent range expansion of coyotes, and the recolonisation of several parts of North America by bobcats following their extirpation. Although studies exploring the dynamics and competition between bobcats and coyotes span decades, there is a lack of understanding regarding what factors influence exploitative or interference competition, and what methodologies are conducive to identifying these types of competition.
2. We gathered a comprehensive list of research papers (n = 41) exploring bobcat–coyote competitive interactions in North America. From them, we collected the following: study site characteristics, number and types of research methods, number and types of metrics explored, history of sympatry of the two species at the study location, presence of apex predators, and documentation of interference and/or exploitative competition.
3. Using generalised linear models, we determined that interference competition between bobcats and coyotes was observed primarily in open habitat. However, habitat heterogeneity, the number of research methods and metrics used, presence of an apex predator, and history of sympatry could not be used to predict the occurrence of interference competition. Studies that included diet overlap were less likely to observe interference competition than studies that used other metrics to infer competition.
4. Competitive interactions between coyotes and bobcats are largely a function of prey availability. Our findings suggest that habitat type may be a surrogate for prey availability, which many researchers mention, but do not explicitly measure. Future studies investigating bobcat–coyote interactions should include the quantification of prey densities to gain a more comprehensive understanding of the system at large, and should avoid using solely diet or habitat overlap as metrics to assess competition.

     

Influences of microhabitat use and foraging mode similarities on intra- and interspecific aggressive interactions in a size-structured stream fish assemblage

Aggressive interactions, foraging behaviour and microhabitat use were observed among four sympatric stream fishes inhabiting the water column: ayu (Plecoglossus altivelis), white-spotted charr (Salvelinus leucomaenis), masu salmon (Oncorhynchus masou) and Japanese dace (Tribolodon hakonensis), each species being categorised into five body-size classes (species-size groups; SSG's). Aggressive interactions were observed between most pairs of SSG's, an almost linear dominance order being apparent throughout the three-month study period. Ayu were relatively subordinate in June, but became the second most dominant in July and the most dominant in August, as a consequence of a reversal in dominance order with salmon. In contrast, smaller-sized dace, which continually suffered from intra- and interspecific aggression, occupied the most subordinate ranks throughout the study period. Intensive aggression was observed among various SSG's, exhibiting same microhabitat propensity throughout the three months. The direction and frequency of aggressive interactions varied month by month due to a reversal in dominance order between ayu and masu salmon, and/or changes in density, body size and resource use of the component members. Opponent selectivity was higher within SSG's, where resource use was assumed to be highly overlapping, rather than among SSG's throughout the study period. Correlation analysis indicated that opponent selectivity in aggressive interactions among SSG's was positively correlated with similarity in microhabitat selectivity in June, but not in other months or with that in foraging habits, suggesting that intensive aggressive behaviour reflected overlapping habitat use among assemblage members during a certain period.     

Energy availability, abundance, energy-use and species richness in forest bird communities: a test of the species–energy theory

Aim To test the ‘more individuals hypothesis’ as a mechanism for the positive association between energy availability and species richness. This hypothesis predicts that total density and energy use in communities is linearly related to energy availability, and that species richness is a positive function of increased density. We also evaluate whether similar energy–density patterns apply to different migratory groups (residents, short‐distance migrants and tropical migrants) separately. Location European and North American forest bird communities. Methods We collected published breeding bird census data from Europe and North America (n = 187). From each census data we calculated bird density (pairs 10 ha^?1), energy use by the community (the sum of metabolic needs of individuals, Watts 10 ha^?1) and geographical location with an accuracy of 0.5°. For each bird census data coordinate we extracted the corresponding monthly values of actual evapotranspiration (AET). From these values we calculated corresponding AET values that we expected to explain the density energy use of forest birds: total annual, breeding season (June) and winter AET. We used general linear modelling to analyse these data controlling for the area of census plots, forest type and census method. Results Total density and energy use in European and North American forest bird communities were linear functions of annual productivity, and increased density and energy use then translated into more species. Also resident bird density and energy consumption were positive functions of annual productivity, but the relationship between productivity and density as well as between productivity and energy use was weaker for migrants. Main conclusions Our results are consistent with the more individuals hypothesis that density and energy use in breeding forest bird communities is coupled tightly with the productivity of the environment, and that increased density and energy consumption results in more species. However, not all community members (migratory groups) are limited by productivity on the breeding grounds.     

Coexistence between two fruit fly species is supported by the different strength of intra‐ and interspecific competition

1. Unravelling the strength and modes of interspecific interactions between resident and introduced species is necessary in order to understand the basis of their coexistence or the displacement of the former by the latter. In Argentina, the indigenous Tephritidae fly Anastrepha fraterculus overlaps its distribution and host fruit with the introduced species Ceratitis capitata. 2. This study focused on the relative strength of intra‐ and interspecific competition during the larval stage as a potential factor supporting coexistence. Classical competition experiments (addition and substitution) were conducted between larvae of the two species reared in artificial larval diet. The study evaluated whether a temporal separation between oviposition events affects the outcome of the competition. 3. When both species started to consume the resource at the same time, A. fraterculus experienced a negative effect in larval survival, pupal weight and duration of larval stage, while for C. capitata, pupal weight decreased. When A. fraterculus started feeding 1 day earlier than C. capitata, the negative effects became milder, and when the temporal separation increased, these effects were reversed. Substitution experiments showed an increase in pupal weight when larvae had to share the resource with heterospecific larvae, and showed negative effects suffered for both species when they shared the resource with conspecific individuals. 4. These results suggest that intraspecific competition is stronger than interspecific competition, and a differential oviposition preference could generate an asynchrony of these species in nature. Such mechanisms could favour coexistence between A. fraterculus and C. capitata in an environment previously occupied only by the former.     

Competitive strategies between Anastrepha fraterculus and Anastrepha obliqua (Diptera: Tephritidae) regulating the use of host fruits

Interspecific competition between individuals of different species can result in reductions in their fecundity, growth or survival, reflecting differential exploitation of resources that become intensified due to spatial co-occurrence, ecological similarity and increased population densities. As two species cannot occupy the same niche, coexistence is only possible if the available resources are used in non-overlapping manners such as niche partitioning or the use of refuges. Among agricultural insect pests, such as fruit flies of the family Tephritidae, competitive interactions can result in competitive displacement, host changes, or the expansion or restriction of the numbers of hosts utilized that can have negative consequences for human agricultural activities. We evaluated the competitive interactions between two fruit fly species of the genus Anastrepha, Anastrepha obliqua (Macquart, 1835) and Anastrepha fraterculus (Wiedmann, 1830), on their respective preferred hosts (mangoes and guava). Experiments of larval competition and competition for ovipositioning sites by adult females were performed to compare the parameters of larval development time, numbers of pupae and emerged adults and numbers of ovipositions in the presence or absence of interspecific competition. We observed that the interactions between those species were asymmetrical and hierarchical, and our results suggest a competitive displacement of A. fraterculus by A. obliqua when those two species are present on the same fruit, whether mangoes or guavas.     

Mechanisms of competition between tadpoles of Australian frogs (Litoria spp.) and invasive cane toads (Rhinella marina)

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A probability-based analysis of temporal and spatial co-occurrence in grassland birds

Aim To test for non‐random co‐occurrence in 36 species of grassland birds using a new metric and the C‐score. The analysis used presence–absence data of birds distributed among 305 sites (or landscapes) over a period of 35 years. This analysis departs from traditional analyses of species co‐occurrence in its use of temporal data and of individual species’ probabilities of occurrence to derive analytically the expected co‐occurrence between paired species. Location Great Plains region, USA. Methods Presence–absence data for the bird species were obtained from the North American Breeding Bird Survey. The analysis was restricted to species pairs whose geographic ranges overlapped. Each of 541 species pairs was classified as a positive, negative, or non‐significant association depending on the mean difference between the observed and expected frequencies of co‐occurrence over the 35‐year time‐span. Results Of the 541 species pairs that were examined, 202 to 293 (37–54%) were positively associated, depending on which of two null models was used. However, only a few species pairs (<5%) were negatively associated. An additional 89 species pairs did not have overlapping ranges and hence represented de facto negative associations. The results from analyses based on C‐scores generally agreed with the analyses based on the difference between observed and expected co‐occurrence, although the latter analyses were slightly more powerful. Main conclusions Grassland birds within the Great Plains region are primarily distributed among landscapes either independently or in conjunction with one another. Only a few species pairs exhibited repulsed or segregated distributions. This indicates that the shared preference for grassland habitat may be more important in producing coexistence than are negative species interactions in preventing it. The large number of non‐significant associations may represent random associations and thereby indicate that the presence/absence of other grassland bird species may have little effect on whether a given focal species is also found within the landscape. In a broader context, the probability‐based approach used in this study may be useful in future studies of species co‐occurrence.