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Interference Competition (interference + competition)
Selected AbstractsDNA analysis on fox faeces and competition induced niche shiftsMOLECULAR ECOLOGY, Issue 8 2004LOVE DALÉN Abstract Interference competition can force inferior competitors to change their distribution patterns. It is, however, possible that the dominant competitor poses a higher threat during certain times of the year, for example during reproduction. In such cases, the inferior competitor is expected to change its distribution accordingly. We used a molecular species identification method on faeces to investigate how the spatial overlap between arctic and red foxes changes between seasons. The results show that arctic and red foxes are sympatric during winter, but allopatric in summer as arctic foxes retreat to higher altitudes further from the tree-line during the breeding season. [source] Do competitive intraguild interactions affect space and habitat use by small carnivores in a forested landscape?ECOGRAPHY, Issue 4 2006Caroline St-Pierre Complex interactions such as interference competition and predation, including intraguild predation, are now recognized as important components in animal community structure. At the lower end of a guild, weasels may be highly affected by other guild members due to small body size in relation to other predators. In 2000 and 2001, we radio-collared 24 ermines Mustela erminea and 25 long-tailed weasels M. frenata in 2 areas that differed in abundance of guild members. We tested the hypothesis that when faced with an increased density of other guild members, weasels would modify space and habitat use to reduce the risk of predation associated with encounters involving guild members. We predicted that weasels would increase use of specific habitats (such as refuges) to reduce encounter rates in the presence of a greater number of guild members. Because M. erminea is smaller than M. frenata and thus better able to take advantage of small rodent burrows as refuges from predators and as feeding grounds, we also predicted that M. frenata would show a stronger response to a higher abundance of guild members than M. erminea. Results were consistent with our predictions. Faced with an increased abundance of guild members, M. frenata showed increased habitat selectivity and reduced activity levels, which resulted in increased daily travel distances and increased home ranges. Mustela erminea responded to an increased abundance of guild members through reduced use of preferred habitat which M. frenata already occupied. The contrasting pattern of habitat selection observed between the 2 mustelid species suggested cascading effects, whereby large-predator pressure on M. frenata relaxed pressure of M. frenata on M. erminea. Our results draw attention to the likelihood that competitive intraguild interactions play a facilitating role in M. erminea,M. frenata coexistence. [source] Networks and dominance hierarchies: does interspecific aggression explain flower partitioning among stingless bees?ECOLOGICAL ENTOMOLOGY, Issue 2 2010KAI DWORSCHAK 1. The distribution of consumers among resources (trophic interaction network) may be shaped by asymmetric competition. Dominance hierarchy models predict that asymmetric interference competition leads to a domination of high quality resources by hierarchically superior species. 2. In order to determine the competitive dominance hierarchy and its effect on flower partitioning in a local stingless bee community in Borneo, interspecific aggressions were tested among eight species in arena experiments. 3. All species tested were strongly mutually aggressive in the arena, and the observed interactions were often lethal for one or both opponents. Aggression significantly increased with body size differences between fighting pairs and was asymmetric: larger aggressors were superior over smaller species. Additional aggression tests involved dummies with surface extracts, and results suggest that species- and colony-specific surface profiles are important in triggering the aggressive behaviour. 4. Sixteen stingless bee species were observed foraging on 41 species of flowering plants. The resulting bee,flower interaction network showed a high degree of generalisation (network-level specialisation H2' = 0.11), corresponding to a random, opportunistic distribution of bee species among available flower species. 5. Aggressions on flowers were rare and only occurred at a low level. The dominance hierarchy obtained in the arena experiments did not correlate significantly with plant quality, estimated as the number of flowers per plant or as total bee visitation rate. 6. Our findings suggest that asymmetries in interference competition do not necessarily translate into actual resource partitioning in the context of complex interacting communities. [source] A review of relationships between interspecific competition and invasions in fruit flies (Diptera: Tephritidae)ECOLOGICAL ENTOMOLOGY, Issue 5 2004Pierre-Francois Duyck Abstract., 1. A number of invasions in the family Tephritidae (fruit flies) have been observed worldwide despite quarantine procedures. In this review, the potential importance of interspecific competition and competitive displacement among different tephritid species is evaluated in the context of recent invasions. 2. Where polyphagous tephritid species have been introduced in areas already occupied by a polyphagous tephritid, interspecific competition has resulted in a decrease in number and niche shift of the pre-established species. No reciprocal invasions have been observed. 3. The data on tephritid invasions seem to support a hierarchical mode of competition; however, complete exclusion usually did not occur. Indeed, tephritid distribution and abundance are markedly structured by various abiotic (mostly climatic) and biotic (host plants) factors. 4. The primary determinant of competitive interactions in near-optimal conditions, such as lowlands with abundant fruit plantations, is probably the life-history strategy. The r,K gradient could be used as a predictor of potential invaders, because K traits (such as large adult size) may favour both exploitation and interference competition. 5. For future research, a better understanding of competition mechanisms seems essential. Different species competing in the same area should be compared with respect to: (i) demographic parameters, (ii) the outcome of experimental co-infestations on the same fruit, and (iii) behavioural and chemical interference mechanisms. [source] Biological warfare in the garden pond: tadpoles suppress the growth of mosquito larvaeECOLOGICAL ENTOMOLOGY, Issue 1 2003Allie Mokany Abstract. 1. Although tadpoles and mosquito larvae may compete for scarce resources in natural freshwater systems, the mechanisms involved in such competition remain largely unstudied. 2. Replicated artificial ponds were set up to examine the role of pathogenic interference (water-borne growth inhibitors) in two tadpole,mosquito systems from south-eastern Australia. One system comprised taxa that are commonly sympatric in freshwater ponds (tadpoles of Limnodynastes peronii and larvae of Culex quinquefasciatus) while the other comprised species that co-occur in brackish water ponds (tadpoles of Crinia signifera and larvae of Ochlerotatus australis). 3. Water that had previously contained tadpoles suppressed the rates of survival and pupation of mosquito larvae in both systems. Fungicide reduced or eliminated this effect, suggesting that the growth inhibitors may be fungal organisms (possibly the yeast Rhodotorula glutinis) from tadpole faeces. Fungicide also enhanced growth rates of tadpoles. 4. These results suggest that interference competition between tadpoles and mosquito larvae is mediated by other organisms in some ecological systems. [source] Possible role of reactive chlorine in microbial antagonism and organic matter chlorination in terrestrial environmentsENVIRONMENTAL MICROBIOLOGY, Issue 6 2009Per Bengtson Summary Several studies have demonstrated that extensive formation of organically bound chlorine occurs both in soil and in decaying plant material. Previous studies suggest that enzymatic formation of reactive chlorine outside cells is a major source. However, the ecological role of microbial-induced extracellular chlorination processes remains unclear. In the present paper, we assess whether or not the literature supports the hypothesis that extracellular chlorination is involved in direct antagonism against competitors for the same resources. Our review shows that it is by no means rare that biotic processes create conditions that render biocidal concentrations of reactive chlorine compounds, which suggest that extracellular production of reactive chlorine may have an important role in antagonistic microbial interactions. To test the validity, we searched the UniprotPK database for microorganisms that are known to produce haloperoxidases. It appeared that many of the identified haloperoxidases from terrestrial environments are originating from organisms that are associated with living plants or decomposing plant material. The results of the in silico screening were supported by various field and laboratory studies on natural chlorination. Hence, the ability to produce reactive chlorine seems to be especially common in environments that are known for antibiotic-mediated competition for resources (interference competition). Yet, the ability to produce haloperoxidases is also recorded, for example, for plant endosymbionts and parasites, and there is little or no empirical evidence that suggests that these organisms are antagonistic. [source] DENSITY-DEPENDENT EFFECTS ON ALLELOPATHIC INTERACTIONS IN YEASTEVOLUTION, Issue 3 2008Duncan Greig The ability of rare types to invade populations is important for the maintenance of diversity and spread of beneficial variants. Spatial structure promotes strategies of interference competition by limiting diffusion of interference toxins and resources, often allowing interference competitors to invade when rare. Consistent with previous results in other microbial systems, toxin production by Saccharomyces cerevisiae is advantageous in spatially structured, high-density environments, but not in unstructured environments. However, at low density and at low frequency, rare toxin producers cannot invade populations of common, sensitive, toxin nonproducers. This is because the likelihood of interaction between toxin producers and sensitives depends upon the density and frequency of both competitors. [source] How starvation risk in Redshanks Tringa totanus results in predation mortality from Sparrowhawks Accipiter nisusIBIS, Issue 2008WILL CRESSWELL Redshanks Tringa totanus that are preyed upon by Sparrowhawks Accipiter nisus at the Tyninghame Estuary, Firth of Forth, Scotland, provide an example of how the starvation,predation risk trade-off results in mortality. In this trade-off, animals cannot always optimize anti-predation behaviour because anti-predation behaviours, such as avoiding predators, are usually incompatible with foraging behaviours that might maximize intake rates. Therefore, as animals compensate for starvation risk, predation risk increases. Sparrowhawks are the main direct cause of death in Redshanks at Tyninghame. Sparrowhawk attack rate is determined by Redshank vulnerability, and vulnerability decreases as group size and distance to cover increase, and probably as spacing decreases. But reduction of predation vulnerability reduces feeding rate because areas away from cover are less food-profitable and grouping results in increased interference competition. Increased starvation risk in midwinter means Redshanks are forced to feed on highly profitable prey, Orchestia amphipods, the behaviour of which means that Redshanks are forced to feed vulnerably, in widely spaced groups, close to predator-concealing cover. Therefore, it is the constraints that limit the ability of Redshanks to feed in large, dense flocks away from cover that ultimately lead to mortality. We investigate this hypothesis further by testing the prediction that mortality can be predicted directly by cold weather and population density. We demonstrate that the overall number of Redshanks and the proportion of Redshanks killed increase in cold months when controlling for population size. We also demonstrate that the proportion of Redshanks killed increases when there are fewer Redshanks present, because the success rate of hunting Sparrowhawks increases, probably because effective management of predation risk through flocking is constrained by a low population size. Redshanks therefore provide an example of how directly mortality caused by predation arises from starvation risk and other constraints that prevent animals from optimizing anti-predation behaviour. [source] Parabiotic associations between tropical ants: equal partnership or parasitic exploitation?JOURNAL OF ANIMAL ECOLOGY, Issue 1 2010F. Menzel Summary 1.,The huge diversity of symbiotic associations among animals and/or plants comprises both mutualisms and parasitisms. Most symbioses between social insect species, however, involve social parasites, while mutual benefits have been only suspected for some parabiotic associations , two colonies that share a nest. 2.,In the rainforest of Borneo, we studied parabiotic associations between the ants Crematogaster modiglianii and Camponotus rufifemur. Parabiotic nests were regularly found inside hollow tree trunks, most likely initiated by Cr. modiglianii. This species frequently nested without its partner, whereas we never found non-parabiotic Ca. rufifemur nests. We experimentally investigated potential benefits, potential interference competition for food (as a probable cost), and foraging niches of both species. 3.,The two species never showed aggressive interactions and amicably shared food resources. However, Cr. modiglianii had a wider temporal and spatial foraging range than Ca. rufifemur, always found baits before Ca. rufifemur and recruited more efficiently. Camponotus rufifemur probably benefited from following pheromone trails of Cr. modiglianii. In turn, Ca. rufifemur was significantly more successful in defending the nest against alien ants. Crematogaster modiglianii hence may profit from its partner's defensive abilities. 4.,In neotropical parabioses, epiphytes grown in ,ant-gardens' play a crucial role in the association, e.g. by stabilization of nests. Hemiepiphytic Poikilospermum cordifolium (Cecropiaceae) seedlings and saplings frequently grew in the entrances of parabiotic nests in Borneo, obviously dispersed by the ants. In cafeteria experiments, both parabiotic ants carried its elaiosome-bearing seeds into the nest. However, P. cordifolium does not provide additional nest space, contrasting with neotropical ant-gardens. 5.,The parabiotic association appears beneficial for both ant species, the main benefits being nest initiation by Cr. modiglianii and interspecific trail-following (for Ca. rufifemur), and, in turn, nest defence by Ca. rufifemur (for Cr. modiglianii). However, Ca. rufifemur seems to be more dependent on its partner than vice versa. [source] Ecosystem functioning in stream assemblages from different regions: contrasting responses to variation in detritivore richness, evenness and densityJOURNAL OF ANIMAL ECOLOGY, Issue 3 2008B. G. McKie Summary 1The diversity of species traits in a biological assemblage varies not only with species richness, but also with species evenness and organism density, which together influence the concentration of traits within functional guilds. Potential trait diversity at local scales is also constrained by the regional species pool. Implications of such variation for spatio-temporal variability in biodiversity,ecosystem functioning relationships are likely to be complex, but are poorly understood. 2In microcosm experiments conducted at laboratories in Sweden, Ireland and Romania, we investigated effects of species richness, evenness and density of stream-living detritivores on two related processes: detritivore leaf-processing efficiency (LPE) and growth. Assemblage composition varied among laboratories: one taxonomic order (Plecoptera) was studied in Sweden, whereas two orders, encompassing wider trait variation, were studied in Romania (Trichoptera and Plecoptera) and Ireland (Trichoptera and Isopoda). 3Relationships between density and both LPE and growth ranged from negative to positive across the study species, highlighting the potential for density-dependent variation in process rates to alter ecosystem functioning, but indicating that such effects depend on species identity. 4LPE varied with species diversity in the two more heterogeneous assemblages, but whereas LPE in the Romanian study was generally enhanced as richness increased, LPE in the Irish study increased only in less-even polycultures dominated by particular species. Transgressive overyielding was detected in the Irish experiment, indicating complementary resource use and/or facilitation (complementarity). These mechanisms could not be distinguished from the selection effect in the Romanian study. 5Growth was elevated in Romanian species mixtures, reflecting positive complementarity, but lower than expected growth in some Swedish mixtures was associated with negative complementarity, indicating interspecific interference competition. 6Our results emphasize the potential importance of detritivore diversity for stream ecosystem functioning, but both the effects of diversity on the studied processes, and the mechanisms underlying those effects, were specific to each assemblage and process. Such variability highlights challenges in generalizing impacts of diversity change for functional integrity in streams and other ecosystems in which the occurrence of important species traits fluctuates over relatively small spatio-temporal scales. [source] Density-dependent growth of young-of-the-year Atlantic salmon Salmo salar in Catamaran Brook, New BrunswickJOURNAL OF ANIMAL ECOLOGY, Issue 3 2005I. IMRE Summary 1While density-dependent mortality and emigration have been widely reported in stream salmonid populations, density-dependent growth is less frequently detected. A recent study suggests that density-dependent growth in stream salmonids occurs at low densities, whereas density-dependent mortality and emigration occur at high densities. 2To test the hypothesis that density-dependent growth occurs primarily at low rather than at high densities, we examined the relationship between average fork length and population density of young-of-the-year (YOY) Atlantic salmon at the end of the growing season using a 10-year data set collected on Catamaran Brook, New Brunswick. We tested whether (1) average body size decreases with increasing density; (2) the effect of density on average body size is greatest at low densities; (3) growth rate will decrease most rapidly at low effective densities [,(fork length)2]; (4) density-dependent growth is weaker over space than over time; and (5) the strength of density-dependent growth increases with the size of the habitat unit (i.e. spatial scale) when compared within years, but not between years. 3There was a strong negative relationship between the average body size and population density of YOY Atlantic salmon in the autumn, which was best described by a negative power curve. Similarly, a negative power curve provided the best fit to the relationship between average body size and effective density. Most of the variation in average body size was explained by YOY density, with year, location and the density of 1+ and 2+ salmon accounting for a minor proportion of the variation. 4The strength of density-dependent growth did not differ significantly between comparisons over space vs. time. Consistent with the last prediction, the strength of density-dependent growth increased with increasing spatial scale in the within-year, but not in the between-year comparisons. 5The effect of density on growth was strongest at low population densities, too low to expect interference competition. Stream salmonid populations may be regulated by two mechanisms: density-dependent growth via exploitative competition at low densities, perhaps mediated by predator-induced reductions in drift rate, and density-dependent mortality and emigration via interference competition at high densities. [source] Habitat heterogeneity affects population growth in goshawk Accipiter gentilisJOURNAL OF ANIMAL ECOLOGY, Issue 2 2001Oliver Krüger Summary 1The concept of site-dependent population regulation combines the ideas of Ideal Free Distribution-type of habitat settlement and density dependence in a vital rate mediated by habitat heterogeneity. The latter is also known as habitat heterogeneity hypothesis. Site-dependent population regulation hypothesis predicts that increasing population density should lead to inhabitation of increasingly poor territories and decreasing per capita population growth rate. An alternative mechanism for population regulation in a territorial breeding system is interference competition. However, this would be expected to cause a more even decrease in individual success with increasing density than site-dependent regulation. 2We tested these ideas using long-term (1975,99) population data from a goshawk Accipiter gentilis population in Eastern Westphalia, Germany. 3Goshawk territory occupancy patterns and reproduction parameters support predictions of site-dependent population regulation: territories that were occupied more often and earlier had a higher mean brood size. Fecundity did not decrease with increasing density in best territories. 4Using time-series modelling, we also showed that the most parsimonious model explaining per capita population growth rate included annual mean habitat quality, weather during the chick rearing and autumn period and density as variables. This model explained 63% of the variation in per capita growth rate. The need for including habitat quality in the time-series model provides further support for the idea of site-dependent population regulation in goshawk. [source] Why is mimicry in cuckoo eggs sometimes so poor?JOURNAL OF AVIAN BIOLOGY, Issue 3 2002I propose that the existence of imperfect adaptations (e.g. egg mimicry) in brood parasites and their hosts (e.g. discrimination abilities) could reflect age-dependent territory and nest-site selection patterns of the host. Studies of various passerines indicate that (1) older breeders tend to occupy nest sites of higher quality than do young birds (ideal despotic distribution resulting from interference competition), (2) nest-site selection affects the risk of parasitism in various habitats, (3) egg recognition in passerines has a strong learning component (therefore naive breeders tend to accept whereas older birds tend to reject parasitic eggs). Because young naive birds, who tend to accept parasitic eggs, usually breed in low-quality areas where they are frequently parasitised, while old experienced birds, who tend to reject parasitic eggs, breed in high-quality areas where they are rarely parasitised, the distribution of acceptors and rejecters with respect to the risk of parasitism is non-random, i.e. populations of some host species may consist of heavily parasitised acceptors and weakly parasitised rejecters. Therefore, the selection pressure exerted by the host on the parasite should be weaker than if brood parasitism was randomly distributed among naive and experienced breeders and affect adaptations such as egg mimicry. This could explain the existence of imperfect adaptations in some brood parasite-host systems. [source] Competition between domestic dogs and Ethiopian wolf (Canis simensis) in the Bale Mountains National Park, EthiopiaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2010A. Atickem Abstract The potential effects of the domestic dogs (Canis familiaris) on the Endangered Ethiopian wolf (Canis simensis) through exploitative and interference competition were studied in the Web Valley of Bale Mountains national park between November 2001 and February 2003. All dogs were owned in the study area and no feral dogs were reported or observed during the research period. The diet of domestic dogs was dominated by barley husks and human faeces which contributed 45% and 20.7% of the total 382 meals observed during focal watch observations. Analysis of dog faeces provided similar results with barley husks, human faeces and animal carcasses occurring in 86.8%, 21.4% and 19.4% of the 1200 faecal samples analysed. Both focal watch and faecal analyses revealed that rodents contributed only a very small proportion of the diet of dogs accounting for only 4.2% of the focal watch and 2.8% of the faecal analysis of roaming dogs. As Ethiopian wolves fed almost exclusively on rodent year round, no significant exploitative competition between dogs and wolves were assessed. Only small proportion of the domestic dogs roamed in the Ethiopian wolf range and interference competition did not appear to be a serious threat for the Ethiopian wolf. Résumé De novembre 2001 à février 2003, on a étudié les effets potentiels des chiens domestiques (Canis familiaris) sur le loup d'Ethiopie (Canis simensis) qui est en danger, en raison d'une compétition par exploitation alimentaire ou par interférences, dans la Vallée de Web, dans le Parc National des montagnes de Bale. Tous les chiens de l'étude avaient un propriétaire, et nous n'avons ni rapporté ni observé de chien féral pendant cette période. Le régime alimentaire des chiens comprenait principalement de la balle d'orge et des excréments humains qui composaient respectivement 45% et 20,7% du total des 382 repas observés pendant des observations focalisées. L'analyse des excréments de chiens donne des résultats semblables : la balle d'orge, les excréments humains et les carcasses d'animaux sont présents dans 86,8%, 21,4% et 19,4% des 1 200 échantillons fécaux analysés. Et les observations focalisées et les analyses des crottes ont révélé que les rongeurs ne composent qu'une toute petite proportion du régime des chiens, avec 4,2% des observations et 2,8% des analyses fécales des chiens errant en liberté. Comme les loups d'Ethiopie se nourrissent toute l'année presque exclusivement de rongeurs, nous avons estimé qu'il n'y avait aucune compétition par exploitation significative entre les chiens et les loups. Seule une petite proportion de chiens circulent dans l'aire de distribution du loup d'Ethiopie, et la compétition par interférence a semblé ne pas constituer une menace sérieuse pour le loup d'Ethiopie. [source] The role of water abundance, thermoregulation, perceived predation risk and interference competition in water access by African herbivoresAFRICAN JOURNAL OF ECOLOGY, Issue 3 2008Marion Valeix Abstract In African savannas, surface water can become limiting and an understanding of how animals address the trade-offs between different constraints to access this resource is needed. Here, we describe water access by ten African herbivore species in Hwange National Park, Zimbabwe, and we explore four possible determinants of the observed behaviours: water abundance, thermoregulation, perceived predation risk and interference competition. On average, herbivores were observed to drink in 80% of visits to a waterhole. The probability of drinking was higher in 2003 (474 mm) than in 2004 (770 mm), and at the end of the dry season than at its beginning. For larger species, this probability may also be related to risks of interference competition with elephants or other herbivores. For smaller species, this probability may also be related to the perceived risk of predation. We also investigate the time spent accessing water to drink. The influence of herd size and the presence of young on the time spent accessing water for most species suggests that perceived predation risk plays a role. Thermoregulation also affects this time: during the hottest periods, herbivores spend less time in open areas, unless when wind is strong, probably owing to evapotranspired heat loss. Résumé Dans les savanes africaines, l'eau de surface disponible peut devenir un facteur limitant et il est nécessaire de comprendre comment les animaux agissent face aux différentes contraintes que pose l'accès à cette ressource. Nous décrivons ici l'accès à l'eau de dix herbivores africains du Parc National de Hwange, au Zimbabwe, et nous explorons quatre facteurs qui sont peut-être déterminants dans les comportements observés: l'abondance de l'eau, la thermorégulation, le risque de prédation ressenti et la compétition/ interférence. En moyenne, on a observé que les herbivores buvaient lors de 80% de leurs visites au point d'eau. La probabilité qu'ils boivent étai plus forte en 2003 (474 mm) qu'en 2004 (770 mm), et à la fin de la saison sèche qu'au début. Pour les plus grandes espèces, cette probabilité pourrait aussi être liée aux risques de compétition par interférence avec les éléphants ou d'autres herbivores. Pour les plus petites espèces, cette probabilité pourrait aussi être liée au risque de prédation ressenti. Nous avons aussi étudié le temps passéà se rendre au point d'eau pour y boire. L'influence de la taille du groupe et de la présence de jeunes sur le temps pris par la plupart des espèces pour se rendre au point d'eau laisse penser que la perception du risque de prédation joue un rôle. La thermorégulation affecte aussi cette durée: pendant les périodes les plus chaudes, les herbivores passent moins de temps dans les espaces ouverts, sauf si le vent est fort, probablement à cause de la perte de chaleur par évapotranspiration. [source] The occurrence and ecology of a marine hydrobiid mudsnail in the southern hemisphere: the Knysna Estuary, South AfricaAFRICAN JOURNAL OF ECOLOGY, Issue 3 2002R. S. K. BarnesArticle first published online: 6 AUG 200 Abstract Earlier published records of the gastropod Hydrobia from the warm temperate Knysna Lagoon on the Indian Ocean coast of South Africa are in error. Nevertheless, an animal hitherto identified as an Assiminea (Assimineidae) or as a Tomichia (Pomatiopsidae) is in fact a Hydrobia s.l., and it does occur intertidally within the Knysna system. The same species also occurs in salt pans in the cool temperate Great Berg Estuary on the Atlantic coast of South Africa. This extends the distribution of confirmed species of the dominant coastal hydrobiid mudsnails of the northern hemisphere into the southern hemisphere. H. knysnaensis (Krauss) occurs patchily at low density near the head of the Knysna Estuary in waters of low salinity. This appears to be a suboptimal habitat, and it is suggested that Hydrobia is restricted to this zone as a result of interference competition from potamidid mudwhelks and ocypodid crabs. The prevalence of potamidids and ocypodids in the tropics and in the temperate southern hemisphere may account for the rareness or absence of hydrobiids in these areas. Unlike its equally intertidal relative, the widespread North Atlantic/Arctic H. ulvae, H. knysnaensis develops directly like other Hydrobia. Résumé Les publications faisant état de la présence du gastéropode Hydrobia dans le lagon tempéré chaud de Knysna, sur la côte sud-africaine de l'océan Indien sont erronées. Néanmoins, un animal identifié jusqu'ici comme un Assiminea (Assimineidae) ou comme un Tomichia (Pomatiopsidae), est en fait un Hydrobia s.l. et il apparaît sur l'estran dans le système de Knysna. La même espèce se rencontre aussi dans des cuvettes saumâtres dans l'Estuaire de Great Berg, tempéré frais, sur la côte atlantique d'Afrique du Sud. Ceci élargit vers l'hémisphère sud la distribution d'une espèce confirmée des mollusques côtiers hydrobiinae dominants de l'hémisphère nord. H. knysnaensis (Krauss) se trouve çà et là, en faible quantité, au fond de l'estuaire de Knysna, dans des eaux de faible salinité. Ceci semble être un habitat sub-optimal, et on suggère qu'Hydrobia est confiné dans cette zone suite à la compétition avec les buccins potamilidae et avec les crabes ocypodidae. La prévalence de ces derniers sous les tropiques et dans la partie tempérée de l'hémisphère sud pourrait expliquer la rareté ou l'absence d'hydrobiidae dans ces régions. Contrairement à son parent H. ulvae, qui vit comme lui sur l'estran, très répandu dans l'Atlantique nord et dans l'Arctique, H. knysnaensis se développe directement, comme les autres Hydrobia. [source] Competition and coexistence in sympatric bobcats and pumasJOURNAL OF ZOOLOGY, Issue 3 2009C. C. Hass Abstract Space use and diets of sympatric bobcats Lynx rufus and pumas Puma concolor were compared using sign surveys and scat analysis during 1997,2002 in south-eastern Arizona, USA. Bobcats appeared to use grassland, scrub, riparian and woodland habitats equally, but pumas had higher activity in riparian and woodland habitats. There was little evidence that bobcats avoided pumas in space use. Bobcats ate primarily rodents (33% of items in scats), lagomorphs (32%) and ungulates (16%), whereas pumas ate primarily ungulates (69%) and carnivores (21%). Pumas had a narrower dietary niche breadth than bobcats, and puma diet overlapped bobcat diet by 56%, suggesting that pumas may be more vulnerable to changes in prey density than bobcats. Pumas also killed and consumed bobcats, indicating that interference competition may be manifesting through intraguild predation. [source] Sexual selection for male dominance reduces opportunities for female mate choice in the European bitterling (Rhodeus sericeus)MOLECULAR ECOLOGY, Issue 5 2005M. REICHARD Abstract Sexual selection involves two main mechanisms: intrasexual competition for mates and intersexual mate choice. We experimentally separated intrasexual (male,male interference competition) and intersexual (female choice) components of sexual selection in a freshwater fish, the European bitterling (Rhodeus sericeus). We compared the roles of multiple morphological and behavioural traits in male success in both components of sexual competition, and their relation to male reproductive success, measured as paternity of offspring. Body size was important for both female choice and male,male competition, though females also preferred males that courted more vigorously. However, dominant males often monopolized females regardless of female preference. Subordinate males were not excluded from reproduction and sired some offspring, possibly through sneaked ejaculations. Male dominance and a greater intensity of carotenoid-based red colouration in their iris were the best predictors of male reproductive success. The extent of red iris colouration and parasite load did not have significant effects on female choice, male dominance or male reproductive success. No effect of parasite load on the expression of red eye colouration was detected, though this may have been due to low parasite prevalence in males overall. In conclusion, we showed that even though larger body size was favoured in both intersexual and intrasexual selection, male,male interference competition reduced opportunities for female choice. Females, despite being choosy, had limited control over the paternity of their offspring. Our study highlights the need for reliable measures of male reproductive success in studies of sexual selection. [source] Chemical mediation of reciprocal mother,offspring recognition in the Southern Water Skink (Eulamprus heatwolei)AUSTRAL ECOLOGY, Issue 1 2008MEGAN L. HEAD Abstract Kin recognition has been demonstrated to play an important role in the social structure of a wide range of animals. Most studies to date have examined parent,offspring recognition only in species that provide offspring with direct parental care, however, there are several advantages to parent,offspring recognition even in the absence of direct parental care. In this study we investigated reciprocal mother,offspring recognition in the Australian scincid lizard Eulamprus heatwolei, a species that does not show direct parental care. We examined whether neonates could discriminate between their mothers and unrelated females, and whether females could discriminate between their offspring and unrelated neonates, via chemical cues, using retreat site selection experiments. We conducted trials when neonates were 1 and 4 weeks old to investigate whether responses are maintained as neonates age. We found that both neonates and mothers could discriminate between related and unrelated individuals when neonates were 1 week old. Mothers were more likely to take refuge under tiles treated with the odours of their own offspring, while neonates spent less time in areas treated with the odours of unrelated females. At 4 weeks of age, mothers no longer exhibited discriminatory behaviour between their offspring and unrelated neonates, while neonates were more likely to associate with the odour of any female over the odourless control. We hypothesize that reciprocal mother,offspring recognition in E. heatwolei reduces interference competition between mothers and their offspring and also may be important in habitat selection and territory establishment. [source] Importance of Body Size in Determining Dominance Hierarchies among Diverse Tropical Frugivores1BIOTROPICA, Issue 1 2005Aaron R. French ABSTRACT Most studies examining dominance hierarchies have focused at the intraspecific level. While some examples of interspecific hierarchies have been noted, these have usually been limited to a few species in the same taxonomic group that utilize resources in similar ways. Here, we examine evidence for dominance interference competition among vertebrates comprising a diverse frugivore community, including 19 species of birds, squirrels, and primates in a mature Central African rainforest. A total of 38 fruiting trees from 18 species were observed for 2058 h to record dominance interactions between foraging vertebrates. We show that interference competition occurs within and between taxonomically diverse species of vertebrates at fruiting trees. The resulting cross-taxonomic dominance hierarchy includes larger vertebrates, such as primates and hornbills, as well as smaller ones, such as squirrels and parrots. Within this hierarchy, the dominance rank of each species is highly correlated with body mass, and is shown to significantly affect the number of fruits removed from a given tree. Because a majority of tropical tree species depend on vertebrates to disperse their seeds, and particular vertebrates may preferentially disperse the seeds of specific tree species, results may have important conservation implications for the maintenance of tree diversity in regions where populations of larger frugivores have been depressed or extirpated. [source] | ||||||||||||||||||||||