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Foraging Efficiency (foraging + efficiency)
Selected AbstractsForaging efficiency of a parasitoid of a leaf herbivore is influenced by root herbivory on neighbouring plantsFUNCTIONAL ECOLOGY, Issue 5 2007R. SOLER Summary 1Root feeding insects can influence foliar quality of the host plant, which can affect the development and behaviour of leaf herbivores and parasitoids. Thus far, such interactions have been reported in situations where root and leaf associated organisms share a host-plant. We tested whether root herbivory influences searching behaviour of an above-ground parasitoid when the foliar feeding host of the parasitoid and the root herbivore are feeding on different plants. 2We manipulated the proportion of 25 plants (ranging from 0 to 1) exposed to root herbivory by Delia radicum (neighbouring-plants). Five additional plants were infested above-ground with Pieris brassicae larvae (host-infested plants) and were placed in-between the neighbouring plants. We then released females of the parasitoid Cotesia glomerata which attacks P. brassicae and studied foraging efficiency of the parasitoid. 3Overall, parasitoids located more host-infested plants during the maximum allowed searching time, and found their hosts about three times faster when neighbouring plants were exposed to root herbivory, than when neighbouring plants were not infested with D. radicum. Similar results were found when the host-infested plants were also exposed to root herbivory. 4Our results show that the interaction between an above-ground foliar feeding insect and its parasitoid can be influenced by the presence of non-host herbivores feeding on the roots of neighbouring conspecific plants. [source] Foraging efficiency and vigilance behaviour of impala: the influence of herd size and neighbour densityAFRICAN JOURNAL OF ECOLOGY, Issue 1 2009Sonja M. Smith Abstract Group foraging can be beneficial for ungulates by decreasing the time required for vigilance, but it can also prove costly because of competition. To determine responses to gregarious behaviour, we studied foraging activity and vigilance of impala (Aepyceros melampus) near Kruger National Park, South Africa. We measured time spent foraging, vigilant, moving, grooming, engaging in social interactions and determined herd size and group distribution (i.e. density). We calculated accepted food abundance (AFA), food ingestion rate, steps per minute and percent vigilance for female, bachelor male and herd male impala. There was no relationship between herd size and vigilance, but vigilance decreased with increasing density (t1,311 = 4.91, P <0.0001). Additionally, AFA decreased (t1,61 = 5.96, P <0.0001) and steps per minute increased (t1,311 = 14.38, P < 0.0001) as more individuals fed in close proximity to each other. Impala could be altering their behaviour to accommodate a perceived change in resources because of intraspecific competition and these adjustments might be related more to the distribution of herd members than to herd size. Further studies should examine the behaviour of gregarious animals in relation to the distribution of herd members in addition to group size. Résumé Le fait de se nourrir en groupe peut être avantageux pour les ongulés parce qu'il réduit le temps nécessaire à la surveillance, mais il peut aussi se révéler coûteux en termes de compétition. Pour déterminer les réponses à un comportement grégaire, nous avons étudié l'action de se nourrir et la vigilance chez l'impala (Aepyceros melampus) près du Parc National Kruger, en Afrique du Sud. Nous avons mesuré le temps passéà se nourrir, à surveiller, à se déplacer, au toilettage, à l'engagement dans des interactions sociales, et nous avons déterminé la taille de la harde et la distribution du groupe (c.-à-d. sa densité). Nous avons calculé l'abondance de nourriture acceptée (AFA), le taux d'ingestion de nourriture (FIR), les pas par minute et le pourcentage de vigilance chez les femelles, les mâles célibataires et les impalas mâles en hardes. Il n'y avait pas de relation entre la taille de la harde et la vigilance, mais la vigilance diminuait lorsque la densité augmentait (t1,311 = 4,91, P < 0,0001). De plus, l'AFA diminuait (t1,61 = 5,96, P < 0,0001), et le nombre de pas par minute augmentait (t1,311 = 14,38, P < 0,0001) lorsque des individus plus nombreux se nourrissaient très près les uns des autres. Les impalas pouvaient modifier leur comportement pour s'adapter à la perception d'un changement des ressources dûà la compétition intraspécifique, et ces ajustements pourraient bien être liés plus à la distribution des membres de la harde qu'à sa taille. De nouvelles études devraient examiner le comportement des animaux grégaires en fonction de la distribution des membres de la harde, en plus de la taille du groupe. [source] The ontogeny of handling hard-to-process food in wild brown capuchins (Cebus apella apella): evidence from foraging on the fruit of Maximiliana maripaAMERICAN JOURNAL OF PRIMATOLOGY, Issue 11 2010Noëlle Gunst Abstract We examined age-related differences in wild brown capuchins' foraging efficiency and the food-processing behaviors directed toward maripa palm fruit (Maximiliana maripa). A detailed comparison of the different foraging techniques showed that plucking the fruit from the infructescence constituted the main difficulty of this task. Foraging efficiency tended to increase with age, with a threshold at which sufficient strength allowed immatures by the age of three to reach adult-level efficiency. Youngsters spent more time than older individuals browsing the infructescence and pulling the fruit in an attempt to harvest it. Infants tried to compensate for their inability to pluck fruit by adopting alternative strategies but with low payback, such as gnawing unplucked fruit and opportunistically scrounging others' partially processed food. Although around 2 years of age, young capuchins exhibited all of the behaviors used by adults, they did not reach adult-level proficiency at feeding on maripa until about 3 years (older juveniles). We compared this developmental pattern with that of extractive foraging on beetle larvae (Myelobia sp.) hidden in bamboo stalks, a more difficult food for these monkeys [Gunst N, Boinski S, Fragaszy DM. Behaviour 145:195,229, 2008]. For maripa, the challenge was mainly physical (plucking the fruit) once a tree was encountered, whereas for larvae, the challenge was primarily perceptual (locating the hidden larvae). For both foods, capuchins practice for years before achieving adult-level foraging competence, and the timeline is extended for larvae foraging (until 6 years) compared with maripa (3 years). The differing combinations of opportunities and challenges for learning to forage on these different foods illustrate how young generalist foragers (i.e. exploiting a large number of animal and plant species) may compensate for their low efficiency in extractive foraging tasks by showing earlier competence in processing less difficult but nutritious foods, such as maripa fruit. Am. J. Primatol. 72:960,973, 2010. © 2010 Wiley-Liss, Inc. [source] Web building flexibility of an orb-web spider in a heterogeneous agricultural landscapeECOGRAPHY, Issue 5 2008Dries Bonte Intensification of land-use in agricultural landscapes is responsible for a decline of biodiversity which provide important ecosystem services like pest-control. Changes in landscape composition may also induce behavioural changes of predators in response to variation in the biotic or abiotic environment. By controlling for environmentally confounding factors, we here demonstrate that the orb web spider Araneus diadematus alters its web building behaviour in response to changes in the composition of agricultural landscapes. Thereby, the species increases its foraging efficiency (i.e. investments in silk and web asymmetry) with an increase of agricultural land-use at intermediate spatial scales. This intensification is also related to a decrease in the abundance of larger prey. A negative effect of landscape properties at similar spatial scales on spider fitness was recorded when controlling for relative investments in capture thread length. This study consequently documents the web building flexibility in response to changes in landscape composition, possibly due to changes in prey availability. [source] Arboreal substrates influence foraging in tropical antsECOLOGICAL ENTOMOLOGY, Issue 4 2010NATALIE A. CLAY 1. Physically complex substrates impart significant costs on cursorial central-place foragers in terms of time spent outside the nest and total distance travelled. Ants foraging in trees navigate varied surfaces to access patchy resources, thus providing an appropriate model system for examining interactions between foraging efficiency and substrates. 2. We expected that the speed of recruitment, body size distribution and species richness of foraging arboreal ants would differ predictably among common substrate types occurring on tropical tree trunks. We measured changes in ant abundance and species composition over time at baits placed on bare tree bark, moss-covered bark, and vine-like vegetation appressed to bark. We also measured average body size and body size frequency on the three substrate types. Ants discovered baits sooner and accumulated at baits relatively faster when using vine substrates as the primary foraging trail. Average body size was smaller on vine substrates than on bark. Experimental removal of vine and moss substrates nullified these differences. Contrary to our predictions, species richness and body size distributions did not differ among the three substrate types, due in part to the frequent presence of a few common ground-nesting species at baits on bare bark. 3. Our results collectively indicate that linear substrates facilitate access of foraging ants to patchy resources. Ant use of vine-like substrates appears to be opportunistic; vine use is not confined to certain species nor constrained by body size. [source] Foraging in nature: foraging efficiency and attentiveness in caterpillars with different diet breadthsECOLOGICAL ENTOMOLOGY, Issue 4 2004E. A. Bernays Abstract., 1. Seventy-seven individual last-instar caterpillars foraging in the field were examined for 6 h each. They represented four species of Arctiidae of similar size and habitat use. Two, Hypocrisias minima and Pygarctia roseicapitis, are specialists restricted to particular plant genera. The other two, Grammia geneura and Estigmene acrea, are extreme generalists that use many host plant species from multiple plant families. 2. Parameters of behavioural efficiency were monitored. Generalists spent more time walking, rejected more potential host plants, took longer to decide to feed after inspecting a plant, and took relatively more small feeding bouts compared with specialists. 3. This is the first test of differential foraging efficiency in the field in relation to diet breadth of insects and the data indicate that generalists are less efficient in their foraging activities and may suffer from divided attention. The need for attentiveness to enhance efficiency and thereby reduce ecological risk is discussed. [source] Spatial patterns, temporal variability, and the role of multi-nest colonies in a monogynous Spanish desert antECOLOGICAL ENTOMOLOGY, Issue 1 2002Xim Cerdá Abstract 1.,The colonies of the Spanish desert ant Cataglyphis iberica are polydomous. This study describes the temporal and spatial patterns of the polydomy in this species at two different sites, and presents analyses of its role in reducing the attacks of the queen over sexual brood, and in allowing better habitat exploitation. 2. The spatial distribution of nests was clumped while colonies were distributed randomly. Mean nearest neighbour distance ranged from 3.4 to 7.0 m for nests and from 12.3 to 14.1 m for colonies. Distance of foragers searching for food varied among nests: mean values were between 6.1 and 12.6 m. 3. At both sites, the maximum number of nests per colony occurred in summer, during the maximum activity period of the species. Colonies regrouped at the end of this period but overwintered in several nests. 4. Nest renewal in C. iberica colonies was high and showed great temporal variability: nests changed (open, close, re-open) continuously through the activity season and/or among years. The lifetime of up to 55% of nests was only 1,3 months. 5. Polydomy in C. iberica might decrease the interactions between the queen and the sexual brood. In all colonies excavated just before the mating period, the nest containing the queen did not contain any virgin female. Females were in the queenless nests of the colony. 6. The results also suggest that polydomous C. iberica colonies may enhance habitat exploitation because foraging activity per colony increases with nest number. The relationship between total prey input and foraging efficiency and number of nests per colony attains a plateau or even decreases after a certain colony size (four to six nests). This value agrees with the observed mean number of nests per colony in C. iberica. [source] An economic model of the limits to foraging range in central place foragers with numerical solutions for bumblebeesECOLOGICAL ENTOMOLOGY, Issue 3 2000James E. Cresswell Summary 1. A model is described that evaluates the maximum economic foraging range in central place foragers by using optimality criteria to discriminate between foraging sites at different distances from the forager's central place. 2. The basic model can be varied to suit foragers that optimise either their rate of net energy uptake or their foraging efficiency. 3. The model requires specification of the time and energy budgets of travel and foraging, and of the rewards obtainable at potential foraging sites. 4. The specific case of bumblebees, whose foraging ranges are poorly known, is considered. 5. Numerical solutions of the model for parameter values that represent bumblebees and their forage predict economic foraging ranges exceeding several kilometres. The model demonstrates that economics alone can explain extensive flight ranges in bees. [source] The size,distance relationship in the wood ant Formica rufaECOLOGICAL ENTOMOLOGY, Issue 2 2000Philip J. Wright Summary 1. The size,distance relationship among honeydew-collecting foragers of the red wood ant Formica rufa was investigated. Within the colony territory, the size (as measured by head width) and fresh weight of samples of foragers were determined for ants ascending and descending trees near, and farther from, the central nest mound. 2. The mean size of the ants was significantly higher at far trees than at near trees in six out of the seven colonies investigated, confirming the general presence of the size,distance relationship. 3. In three colonies, a load,distance relationship was also found. For a given head width, honeydew-carrying ants descending far trees were significantly heavier than those descending near trees (i.e. they were carrying heavier loads from trees farther away from the central nest mound). 4. This is the first time that both load,distance and size,distance relationships have been reported in foraging workers from the same ant colony. 5. The combined effects of these characteristics suggest that colony foraging efficiency is enhanced by far trees being visited by the larger workers that then return with heavier loads of honeydew. [source] Foraging specialisms, prey size and life-history patterns: a test of predictions using sympatric polymorphic Arctic charr (Salvelinus alpinus)ECOLOGY OF FRESHWATER FISH, Issue 1 2008D. Fraser Abstract,,, We use arguments based on optimal foraging theory to predict body size constraints and the consequences of these on a range of life-history traits in three trophic specialist morphs of Arctic charr, Salvelinus alpinus, living in sympatry in Loch Rannoch, Scotland. As predicted, foraging specialists feeding on small prey items with a narrow size range showed evidence of deterministic growth; the ultimate body size of macrobenthos feeders being larger (L, = 238 mm) than that of planktivores (L, = 216 mm). In contrast, the piscivorous morph showed no evidence of reaching a maximal body size. The two size-constrained morphs (benthivores and planktivores) matured earlier and died younger (living for up to 11 and 7 years, respectively, in this study) than did the piscivorous charr which showed continuous growth up to at least 17 years. The pattern of annual reproductive investment in maturing individuals was complex. Planktivores invested in larger eggs than the other two forms, but benthivores produced a greater number of eggs than planktivores, which in turn produced more than piscivores. Planktivorous males had a greater investment in mean testis weight than the other two forms. Lifetime reproductive output was the greatest in the benthivorous charr, intermediate in planktivorous and the lowest in the piscivorous charr when measured either as fecundity or as gonadal weight. We conclude that constraints imposed upon foraging specialists by foraging efficiency is a significant driver of body size and ultimately reproductive investment in gape-limited foraging salmonids. [source] Competition for food between Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) over different substrate typesECOLOGY OF FRESHWATER FISH, Issue 4 2004A. Dieterich Abstract,,, Food consumption by Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) was studied in single and mixed-species treatments in the laboratory, where alternative food resources, chironomids and zooplankton, were offered simultaneously. The effects of structural complexity, which was represented by substrate grain size, and of feeding level on food consumption were analysed. Across all experiments, the outcome of competition between perch and ruffe depended on food abundance and on the structural complexity of the environment. Perch and ruffe both changed their food consumption in the presence of a heterospecific competitor. With high food supply, perch consumed more benthic food than ruffe. With low food supply, the consumption of perch decreased strongly, while that of ruffe remained high on fine sediment. Under all conditions tested, the mechanism of competition appeared to be of interference rather than of exploitative nature. It is suggested that with decreasing lake productivity caused by re-oligotrophication, habitat shifts of both species will occur, which will alleviate interspecific competition. Ruffe will forage over fine sediment and perch over coarse sediment, whereby both species will achieve the highest foraging efficiency under conditions of low food supply. Resumen 1. Hemos estudiado el consumo alimenticio de Perca fluviatilis L. y Gymnocephalus cernuus (L.) en condiciones de laboratorio. Bajo tratamientos de especies individuales y mezcladas, les ofrecimos, simultáneamente, varios recursos alimenticios alternativos (quironómidos y zooplancton). 2. Analizamos los efectos de la complejidad estructural - representada por el tamaño del sustrato (arena, grava, y guijo) - y del nivel alimenticio, sobre el consumo alimenticio. Pusimos especial atención a la potencial influencia de competidores hetero-específicos sobre los patrones alimenticios de ambas especies, tanto en términos cualitativos como cuantitativos. Además, dado que en un futuro cercano una menor productividad general en lagos debida a re-oligotrofia, probablemente aumente la competición por el alimento en muchos lagos donde ambas especies co-existen, los experimentos se llevaron a cabo bajo niveles de abastecimiento alimenticio alto y bajo. 3. En los experimentos, la aparición de competencia entre P. fluviatilis y G. cernuus dependió de la abundancia del alimento y de la complejidad estructural del ambiente. El consumo de quironómidos por P. fluviatilis dependió del tipo de sustrato a niveles altos de abastecimiento alimenticio pero no a niveles bajos, mientras que en G. cernuus observamos lo contrario. 4. Ambas especies cambiaron el consumo alimenticio en presencia de un competidor hetero-específico. A altos niveles de abastecimiento alimenticio, P. fluviatilis consumió más bentos que G. cernuus. A niveles bajos, el consumo de P. fluviatilis decreció substancialmente mientras que el de G. cernuus permaneció alto en sedimento fino. Bajo todas las condiciones experimentales analizadas, los mecanismos de competición parecieron ser de interferencia más que de naturaleza explotativa. 5. Finalmente, presentamos un escenario sobre como P. fluviatilis y G. cernuus pueden competir por alimento bentónico en lagos con variado sustrato de fondo. Sugerimos que a altos niveles de abastecimiento alimenticio, G. cernuus forrajee más sobre arena y grava mientras que P. fluviatilis puede utilizar todos los sustratos disponibles. Al decrecer el abastecimiento alimenticio por re-oligotrofia, pueden producirse cambios en el hábitat de ambas especies que minimizarán la competencia inter-específica. G. cernuus forrajeará básicamente sobre sedimento fino, allá donde sea claramente superior a P. fluviatilis. Esta última especie forrajeará predominantemente sobre sedimento más grueso donde se enfrentará a competencia intra- e inter-específica. A través de estos cambios de hábitat, ambas especies podrían alcanzar la mayor eficiencia de forrajeo bajo condiciones de bajo abastecimiento alimenticio. [source] Contrasting Patch Residence Strategy in Two Species of Sit-and-Wait Foragers Under the Same Environment: A Constraint by Life History?ETHOLOGY, Issue 2 2005Tadashi Miyashita The present study explored the significance of life history constraints on patch residence strategy by using two congeneric web spider species living in the same habitat. Nephila maculata had a large body size but had a shorter developmental period compared with N. clavata, indicating that N. maculata should have a greater foraging efficiency to reach maturity and reproduce. Residence time at web-sites in N. maculata was shorter than that in N. clavata, irrespective of the season. However, supplementation of food to N. maculata increased residence time, suggesting that it searches web-sites with higher prey intake. Investment of web materials, an important trait influencing web relocation frequency, was not greater in N. maculata. In addition, microhabitat and prey size did not differ significantly after controlling for the effect of body size. Because N. maculata needs to attain a large body size in a shorter period of time, this species appears to take a risk of moving patches to seek high quality web-sites. [source] Foraging efficiency of a parasitoid of a leaf herbivore is influenced by root herbivory on neighbouring plantsFUNCTIONAL ECOLOGY, Issue 5 2007R. SOLER Summary 1Root feeding insects can influence foliar quality of the host plant, which can affect the development and behaviour of leaf herbivores and parasitoids. Thus far, such interactions have been reported in situations where root and leaf associated organisms share a host-plant. We tested whether root herbivory influences searching behaviour of an above-ground parasitoid when the foliar feeding host of the parasitoid and the root herbivore are feeding on different plants. 2We manipulated the proportion of 25 plants (ranging from 0 to 1) exposed to root herbivory by Delia radicum (neighbouring-plants). Five additional plants were infested above-ground with Pieris brassicae larvae (host-infested plants) and were placed in-between the neighbouring plants. We then released females of the parasitoid Cotesia glomerata which attacks P. brassicae and studied foraging efficiency of the parasitoid. 3Overall, parasitoids located more host-infested plants during the maximum allowed searching time, and found their hosts about three times faster when neighbouring plants were exposed to root herbivory, than when neighbouring plants were not infested with D. radicum. Similar results were found when the host-infested plants were also exposed to root herbivory. 4Our results show that the interaction between an above-ground foliar feeding insect and its parasitoid can be influenced by the presence of non-host herbivores feeding on the roots of neighbouring conspecific plants. [source] The visual fields of two ground-foraging birds, House Finches and House Sparrows, allow for simultaneous foraging and anti-predator vigilanceIBIS, Issue 4 2008ESTEBAN FERNÁNDEZ-JURICIC In birds, differences in the extent and position of the binocular visual field reflect adaptations to varying foraging strategies, and the extent of the lateral portion of the field may reflect anti-predator strategies. The goal of this study was to describe and compare the visual fields of two ground-foraging passerines, House Finch Carpodacus mexicanus and House Sparrow Passer domesticus. We found that both species have a binocular field type that is associated with the accurate control of bill position when pecking. Both species have eye movements of relatively large amplitude, which can produce substantial variations in the configuration of the binocular fields. We propose that in these ground foragers, their relatively wide binocular fields could function to increase foraging efficiency by locating multiple rather than single food items prior to pecking events. The lateral fields of both species are wide enough to facilitate the detection of predators or conspecifics while head-down foraging. This suggests that foraging and scanning are not mutually exclusive activities in these species, as previously assumed. Furthermore, we found some slight, but significant, differences between species: House Sparrow binocular fields are both wider and vertically taller, and the blind area is wider than in House Finches. These differences may be related to variations in the degree of eye movements and position of the orbits in the skull. [source] Age-dependent reproductive performance in Northern Goshawks Accipiter gentilisIBIS, Issue 1 2003Jan Tøttrup Nielsen The age-specific reproductive performance of Northern Goshawks Accipiter gentilis was studied over 22 years in Denmark. The age of the breeding female in relation to the number of young raised was known in 929 breeding attempts, while the age of both the male and the female was known in 496 breeding attempts. The number of fledglings raised per breeding attempt increased with both male and female age, but only for females was it possible to conduct a detailed analysis of this age-dependent relationship. The annual production of fledglings increased with female age from 1 to 7 years of age, whereupon it started to decline. A longitudinal analysis showed that this mean population trend could be attributed to similar age-related trends in individual females. Previous breeding experience did not influence the number of fledglings produced by individual females, and poorly performing females apparently survived with the same probability as well performing ones. The most likely explanation for the age-dependent reproductive performance in the observed Goshawk population appeared to be age-related improvements in competence, such as foraging efficiency. [source] Testing mechanisms of coexistence among two species of frugivorous primatesJOURNAL OF ANIMAL ECOLOGY, Issue 4 2006ALAIN HOULE Summary 1We examined mechanisms of coexistence between two congeneric species of frugivorous primates, the blue monkey (Cercopithecus mitis) and the red-tailed monkey (C. ascanius). 2We used giving-up densities (the amount of food which animals leave in a patch) in fruit trees to measure foraging efficiency and to evaluate possible mechanisms of coexistence. Animals with higher giving-up densities are less likely to persist in the company of those with lower giving-up densities because the former are not able to exploit food patches used previously by the latter. We climbed trees to estimate giving-up densities by counting the fruit which primates left behind. 3We tested five possible mechanisms of coexistence. Three mechanisms proposed that each frugivorous species has a lower giving-up density than the other in at least one of the following: (1) different tree species, (2) within-tree foraging zones or (3) seasons. The fourth mechanism predicted that the socially dominant species exploits resources first and that the subordinate species has lower giving-up densities. The final mechanism predicted that one species would find resources more quickly than the other, which would in turn have a lower giving-up density. 4Four of the five mechanisms received no support from our data. Only a trade-off between interspecific dominance and giving-up densities was supported. 5We discuss the generality of our results and possible interactions with other factors. [source] Landscape complementation and food limitation of large herbivores: habitat-related constraints on the foraging efficiency of wild pigsJOURNAL OF ANIMAL ECOLOGY, Issue 1 2003David Choquenot Summary 1The effect that the proximity of habitats containing essential resources has on animal abundance at large spatial scales is called landscape complementation. Landscape complementation can influence interaction between large herbivores and their food resources where the proximity of habitats containing essential resources constrains their foraging or demographic efficiency. 2We tested the effect that the proximity of a thermal refuge (riverine woodlands) had on interaction between wild pigs and their food resources (pasture). The numerical response of pigs (Sus scrofa L.) (estimated as r quarter,1) to pasture biomass was contrasted between four sites that were progressively more isolated from a major floodplain containing extensive areas of riverine woodland. To test whether proximity to riverine woodlands affected the numerical response of pigs through a constraint on foraging efficiency, we contrasted the numerical response of pigs between the four areas as pasture biomass declined. To test whether pigs exploited riverine woodlands primarily as a thermal refuge, we contrasted the numerical response of pigs between the four areas in different seasons. 3We found that although pasture biomass was similar in the four areas, r was lower than expected for given pasture biomass on the two areas further away from riverine woodlands. We also found that while the effect that proximity to riverine woodlands had on the numerical response of pigs became more pronounced when pasture biomass was low, it was not significantly affected by season. 4These results suggest that the need to access riverine woodlands compromises the foraging efficiency of wild pigs when the distance to this habitat is relatively high, but that the need to access this habitat may not be purely related to thermoregulation. 5We developed a simple mechanistic model that allows the effects of landscape complementation on herbivore foraging and demographic efficiency to be estimated, and used the model to predict the effect that proximity to riverine woodlands would have on variation in pig density. The model suggests that wild pigs cannot persist in areas more then 10 km from extensive riverine woodlands, unless those areas are periodically re-colonized. This suggests that at the margin of their range around inland river systems, given locations that can be occupied by wild pigs will vary temporally between being sources, pseudosinks and sinks. [source] Sex-specific food provisioning in a monomorphic seabird, the common guillemot Uria aalge: nest defence, foraging efficiency or parental effort?JOURNAL OF AVIAN BIOLOGY, Issue 1 2009Chris B. Thaxter Sexual differences in food provisioning rates of monomorphic seabirds are well known but poorly understood. Here, we address three hypotheses that attempt to explain female-biased food provisioning in common guillemots Uria aalge: (1) males spend more time in nest defence, (2) females have greater foraging efficiency, and (3) males allocate a greater proportion of foraging effort to self-maintenance. We found that males spent no more time with chicks than females but made longer trips and travelled further from the colony. There was extensive overlap between sexes in core foraging areas, indicating that females were not excluding males from feeding opportunities close to the colony. However, as a result of their longer trips, the total foraging areas of males were much greater than those of females. There was no difference between sexes in overall dive rate per hour at sea, in behaviour during individual dives or in a number of other measures of foraging efficiency including the frequency, depth and duration of dives and the dive: pause ratio during the final dive bout of each trip, which was presumably used by both sexes to obtain prey for the chick. These data strongly suggest that sexes did not differ in their ability to locate and capture prey. Yet males made almost twice as many dives per trip as females, suggesting that males made more dives than females for their own benefit. These results support the hypothesis that female-biased food provisioning arose from a difference between sexes in the allocation of foraging effort between parents and offspring, in anticipation of a prolonged period of male-only post-fledging care of the chick, and not from differences in foraging efficiency or time spent in nest defence. [source] Use of arboreal and terrestrial space by a small mammal community in a tropical rain forest in Borneo, MalaysiaJOURNAL OF BIOGEOGRAPHY, Issue 4 2004Konstans Wells Abstract Aim, Small mammals were live-trapped in a primary rain forest to evaluate the relative distribution of species to each other and to microhabitat properties on the ground and in the canopy. Location, Kinabalu National Park in Borneo, Sabah, Malaysia. Methods, Seven trapping sessions were conducted along two grids with 31 trap points at distances of 20 m on the ground and in the lower canopy at an average height of 13.5 m. Results, Species diversity and abundance of small mammals proved to be high: 20 species of the families Muridae, Sciuridae, Tupaiidae, Hystricidae, Viverridae and Lorisidae were trapped, with murids being dominant in both habitat layers. The terrestrial community was significantly more diverse with 16 captured species (Shannon,Wiener's diversity index = 2.47), while 11 species were trapped in the canopy ( = 1.59). The Whitehead's rat, Maxomys whiteheadi, and the red spiny rat, Maxomys surifer, dominated the terrestrial community whereas the large pencil-tailed tree mouse, Chiropodomys major, was by far the most abundant species in the canopy. Other abundant species of the canopy community, the dark-tailed tree rat, Niviventer cremoriventer, and the lesser treeshrew, Tupaia minor, were also abundant on the ground, and there was no clear boundary between arboreal and terrestrial species occurrences. Main conclusions, As most species were not confined to specific microhabitats or habitat layers, species seemed to rely on resources not necessarily restricted to certain microhabitats or habitat layers, and separation of species probably resulted mainly from a species' concentrated activity in a preferred microhabitat rather than from principal adaptations to certain habitats. Ecological segregation was stronger in the more diverse terrestrial community, though microhabitat selection was generally not sufficient to explain the co-occurrences of species and the variability between local species assemblages. Constraints on small mammal foraging efficiency in the three-dimensional more complex canopy may be responsible for the similarity of microhabitat use of all common arboreal species. Community composition was characterized by mobile species with low persistence rates, resulting in a high degree of variability in local species assemblages with similar turnover rates in both habitats. [source] Lethal and sub-lethal effects of spinosad on bumble bees (Bombus impatiens Cresson)PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 7 2005Lora A Morandin Abstract Recent developments of new families of pesticides and growing awareness of the importance of wild pollinators for crop pollination have stimulated interest in potential effects of novel pesticides on wild bees. Yet pesticide toxicity studies on wild bees remain rare, and few studies have included long-term monitoring of bumble bee colonies or testing of foraging ability after pesticide exposure. Larval bees feeding on exogenous pollen and exposed to pesticides during development may result in lethal or sub-lethal effects during the adult stage. We tested the effects of a naturally derived biopesticide, spinosad, on bumble bee (Bombus impatiens Cresson) colony health, including adult mortality, brood development, weights of emerging bees and foraging efficiency of adults that underwent larval development during exposure to spinosad. We monitored colonies from an early stage, over a 10-week period, and fed spinosad to colonies in pollen at four levels: control, 0.2, 0.8 and 8.0 mg kg,1, during weeks 2 through 5 of the experiment. At concentrations that bees would likely encounter in pollen in the wild (0.2,0.8 mg kg,1) we detected minimal negative effects to bumble bee colonies. Brood and adult mortality was high at 8.0 mg kg,1 spinosad, about twice the level that bees would be exposed to in a ,worst case' field scenario, resulting in colony death two to four weeks after initial pesticide exposure. At more realistic concentrations there were potentially important sub-lethal effects. Adult worker bees exposed to spinosad during larval development at 0.8 mg kg,1 were slower foragers on artificial complex flower arrays than bees from low or no spinosad treated colonies. Inclusion of similar sub-lethal assays to detect effects of pesticides on pollinators would aid in development of environmentally responsible pest management strategies. Copyright © 2005 Society of Chemical Industry [source] | |||||||||||||||||||||||||