Foraging Competition Research Articles

Does variation in plant diversity and abundance influence browsing intensity in black rhinos?

AbstractVariations in forage availability, selection and preferences can lead to intense foraging competition and depletion of food consequently lowering diet quality and population performance of black rhino species. This study investigated seasonal variations in rhino diet, foraging, preference and browsing intensity and how this is influenced by plant diversity and availability in Mkomazi National Park (MKONAPA). Fifty‐eight square grids were randomly selected in each season, and plots were laid for vegetation assessment during wet and dry seasons in the sanctuary. Browsed species by rhinos were compared with rhino feeding data from fourteen rhino range areas within Africa. More than 85% of species edible in MKONAPA were similar to those in rhino range areas. Acalypha ornata, Grewia similis and Commiphora africana were highly utilised specie in both seasons. Diversity and abundance of consumed browses decreased towards the dry season while browsing intensity increased with forage preference in both seasons and was prominent when browse availability was low in dry seasons. Our study established seasonal variation in dietary composition, browsing intensity and preferences for black rhinos. We suggest establishing nutritional composition of preferred forages, assessing density of competitor browsers, translocating excess rhinos or expanding the sanctuary to meet the recommended ecological carrying capacity.

Interspecific interactions among three species of sea turtle using a common resting area.

Interspecific interactions among three species of sea turtle using a common resting area.

Modelling foraging competition between solitarious and gregarious organisms in increasingly heterogeneous environments

Density dependent phase polyphenism is the exhibiting of two or more distinct phenotypes from a single genotype depending on local population density. The most well known insect to exhibit this phenomenon is the locust, with whom the profound effect on behaviour leads to the classification of the two phases; solitarious, where locusts actively avoid other locusts, and gregarious, where locusts are strongly attracted to other locusts. It has been shown that food distributions at both small and large scales have an effect on the process of gregarisation. While gregarisation offers advantages, such as greater predator avoidance, the relationship between phase polyphenism and potential foraging benefits is still not fully understood.In this paper, we explore the effect of gregarisation on foraging within increasingly heterogeneous environments using a partial differential equation model. We first consider a single two dimensional simulation of a spatially heterogeneous environment to understand the mechanics of gregarious/solitarious foraging. We then look at the steady state foraging advantage (measured as the ratio of per-capita contact with food) in environments ranging from homogeneous to very spatially heterogeneous. Finally, we perform a parameter sensitivity analysis to find which model parameters have the greatest effect on foraging advantage. We find that during the aggregation stage, prior to the onset of marching (which we do not model here), in increasingly heterogeneous food environments it is better to be gregarious than solitarious. In addition, we find that this is intrinsic to the gregarious/solitarious behavioural dynamic as it occurs almost regardless of the model parameters. That is to say, it doesn’t matter how fast the organisms disperse or how strong their long range interactions as long as there is the solitarious/gregarious behaviour the gregarious foraging advantage will exist.

Uncertain foraging opportunities and predation risk exert additive effects on induced neophobia in cichlids

Neophobia is defined as the avoidance of novel or unknown stimuli, including unknown predators, and can be induced by exposure to uncertain ecological conditions. In addition to uncertainty related to predation risk, uncertainty may also arise from increased foraging competition. Prey forced to spend time and energy competing for limited resources may not have enough time available to devote to predator identification and hence benefit from increased neophobia. Here, we tested the potential interaction of reduced foraging opportunities and elevated predation risk on the strength of neophobia (the antipredator response towards a novel chemical cue). In our first experiment, shoals of juvenile convict cichlids, Amatitlania nigrofasciata , were exposed to high (10% total body weight/day) or low (1% total body weight/day) relative food abundance for 7 days. During the final 3 days, we exposed the shoals to high versus low background predation risk, resulting in a 2 × 2 design. We found that while low food abundance alone and risk alone induced a weak neophobic response to a novel cue (versus water control), cichlids pre-exposed to high risk and low food abundance exhibited significantly a stronger neophobic response, in an additive pattern. In our second experiment, we exposed shoals of cichlids to a fixed amount of food distributed on a single (high competition) patch or across five (low competition) patches for 7 days, with the same risk manipulation as above for the final 3 days. As in experiment 1, we found that high competition alone and risk alone elicited a weak neophobic response to novel cues and that high risk and high competition had additive effects on the strength of induced neophobia among juvenile cichlids. Together, our results indicate that uncertainty of risk and of foraging opportunities exert additive effects on the phenotypically plastic neophobia among prey populations. • Neophobia should reduce costs of bad decisions under uncertain conditions. • Increased competition should increase uncertainty of foraging opportunities. • We exposed cichlids to high vs low predation risk under high vs low competition. • Neophobic responses were stronger under high competition. • Uncertain risk and foraging opportunities exert additive effects on neophobia.

Effect of high population density of eastern black rhinoceros, a mega‐browser, on the quality of its diet

AbstractHigh density of herbivore populations can lead to intense foraging competition and depletion of food consequently lowering diet quality and population performance. We tested for the effects of the density of eastern black rhinoceros (Diceros bicornis michaeli) in ninein situpopulations of 0.01–0.7 individuals per km2density range on the quality of their diet while controlling for plant available moisture and plant available nutrients. We used faecal calcium, phosphorus, copper and zinc concentrations as proxy indices for dietary quality from 473 fresh faecal samples obtained from 77 adult animalsin situ, after determining a positive faeces‐diet mineral correlation in feeding trials with black rhinoceros in zoos. Some populations surpassed 70%–80% of their estimated maximum stocking densities expected to cause impact on forage. However, we did not find significant correlation between rhino population density and dietary quality, as measured via faecal mineral nutrient content. This suggests that black rhinoceros may have sufficient behavioural plasticity to adjust their diet to cover their nutritional requirements when density increases. Instead, 1‐month lagged plant available moisture, reflecting precipitation over the 4 weeks preceding each sampling effort, significantly explained the mineral concentrations in the faeces. By contrast, plant available nutrients had no effect.

Personality‐dependent inter‐ and intraspecific foraging competition in the invasive round goby, Neogobius melanostomus

This study examines the impact of boldness on foraging competition of the highly invasive round goby Neogobius melanostomus Pallas 1815. Individual risk tolerance, or boldness, was measured as the time to resume movement after a simulated predation strike. Fish that resumed movement faster were categorized as "bold," fish that took more time to resume movement were categorized as "shy" and those that fell in between these two categories were determined to have "intermediate" boldness. Competitive impacts of boldness in N. melanostomus were determined in a laboratory foraging experiment in which interspecific (juvenile Atlantic cod Gadus morhua Linnaeus 1758) and intraspecific (intermediate N. melanostomus) individuals were exposed to either bold or shy N. melanostomus competitors. G. morhua consumed fewer prey when competing with bold N. melanostomus than when competing with shy N. melanostomus, whereas intermediately bold N. melanostomus foraging was not affected by competitor boldness. Bold and shy N. melanostomus consumed similar amounts of prey, and the number of interactions between paired fish did not vary depending on the personality of N. melanostomus individuals. Therefore, intraspecific foraging competition was not found to be personality dependent. This study provides evidence that individual differences in boldness can mediate competitive interactions in N. melanostomus; nonetheless, results also show that competition is also governed by other mechanisms that require further study.

Comparative growth, feeding and reproduction of hatchery-reared and wild mandarin fish Siniperca chuatsi in a shallow Yangtze lake, China

Stocking hatchery-reared fish in natural shallow lakes is a common practice in Chinese fisheries. The success of these fisheries depends on the balance between the commercial value of the stock and the growth performance of stocked fish to rapidly reach commercial size. The mandarin fish Siniperca chuatsi has become a commercially important fishery in China. However, the performance of hatchery-reared mandarin fish (HMF) after release into natural environments and their interactions with wild mandarin fish (WMF) have received little attention. In this study, we compared the growth, feeding and reproduction of HMF with WMF in a shallow Yangtze lake. We found that 11 mo after release, the growth of HMF was significantly slower than that of WMF but rapidly caught up after 16-19 mo. This suggests that HMF may experience compensatory growth after 11 mo, which may be a result of a low reproductive investment compared to WMF. In addition, the trophic niche of HMF differed significantly from that of WMF, with a lower diversity of prey and a single dominant prey species. Furthermore, there was no significant diet overlap between HMF and WMF. Our findings demonstrated that the growth performance of HMF can equal or exceeded that of wild conspecifics, and that there was limited diet overlap with WMF, suggesting that the current stock enhancement programmes of releasing HMF can result in fish similar to that of WMF, with limited foraging competition.

Niche overlap and dietary resource partitioning in an African large carnivore guild

AbstractUnderstanding and quantifying a large carnivores’ feeding behaviour is a key component in determining its functional significance in an ecosystem, both in terms of its top‐down influence on prey species, but also its relationships with sympatric carnivores. Dietary overlap is one of the numerous niche dimensions used to characterize resource partitioning and potential competition within a community. We characterize the diet, potential dietary niche overlap and prey preference of a large African carnivore guild on small fenced protected areas. To quantify the potential inter‐ and intraspecific foraging competition, we analysed 5,128 kills, representing 35 prey species made by African wild dogs Lycaon pictus (n = 553), cheetahs Acinonyx jubatus (1,427), lions Panthera leo (2,648) and leopards P. pardus (500). Our results show that large African carnivores in small protected areas are exposed to considerable overlap in dietary resource utilization. At the interspecific level, African wild dogs and cheetahs displayed the greatest vulnerability to potential dietary competition. Lions exhibited marked differences in prey preference, mass and species utilization compared to the other carnivores. African wild dogs and cheetah females with dependent offspring occupied the greatest potential for dietary competition within the large carnivore guild. Using a case study based on the preferred biomass of prey available, we estimate the sustainable density of large carnivores at a small fenced prospective African wild dog reintroduction site. African wild dogs displayed the lowest mean predicted density compared to all sympatric predators with an expected population size of 7 individuals. Our research highlights the need to assess the influence of competitive forces in structuring and restoring large predators to portions of their historical range by identifying species most vulnerable to a potential reintroduction attempt. In the absence of controlled experiments, elucidating the influences of exploitation competition is challenging, and only through manipulating sympatric species presence and densities can these complex interactions be fully understood.

Barnyardgrass Root Recognition Behaviour for Rice Allelopathy

Recent studies have demonstrated that the presence of belowground neighbours induces varied morphological and biochemical responses in plants. Plant allelopathic activity is elicited by the presence of competitor seedlings or competitor root exudates. However, it is unknown whether allelopathy also influences root recognition behaviour in weed–crop interaction. To assess barnyardgrass response to the presence of allelopathic rice roots, we conducted a greenhouse experiment of barnyardgrass–rice mixed culture, including barnyardgrass monoculture, barnyardgrass mixed with the allelopathic rice line PI312777 and barnyardgrass mixed with the nonallelopathic rice cultivar Liaojing-9. Our results showed that the presence of allelopathic rice roots enhanced root allocation and tissue density (RTD) of barnyardgrass, whereas it decreased root biomass, total root length, specific root length (SRL) and topological index (TI), compared to barnyardgrass grown in monoculture; moreover, there was a significant correlation of topological index with root foraging precision and competition. Therefore, the presence of allelopathic rice roots affected the barnyardgrass root morphology, nutrient foraging and competition, suggesting that allelopathy plays a key role in root recognition behaviour of barnyardgrass–rice competitive interaction.

Martu ethnoarchaeology: Foraging ecology and the marginal value of site structure

Archaeological investigations of hunter-gatherer site structure have remained largely descriptive, despite significant explanatory advancements by evolutionary approaches to foraging behavior and ecology. To date, calls to incorporate site structure studies within this behavioral ecological framework have largely been ignored. We suggest there is a clear explanation for this. At large spatial extents, human behavior is constrained by patterned ecological variability, as such, a general theory of behavior is likely to characterize key aspects of human decisions. At small spatial extents, human behavior is not constrained by patterned ecological variability, therefore, the human decisions that produce site structure should be driven by mechanical constraints or random variation. However, variation in site structure may be ecologically relevant inasmuch as it informs on landscape level variation in human-environment interactions. Drawing on ethnoarchaeological data collected in collaboration with Martu, Aboriginal foragers in Western Australia, here we test empirically-derived, mechanistic predictions on site size and material size sorting to show how these can inform theoretically-derived, adaptive predictions from the Marginal Value Theorem. Results show that site size increases with the number of occupants and hence, the amount of in-patch foraging competition, while size sorting increases with the duration of occupation and hence, in-patch residence time. Combined, these attributes of site structure can be used as proxies of foraging behavior to explain variability in overall foraging yields. With this approach, site structure can provide insights into foraging decisions that can be examined through a general theory of behavior.

Robbing rivals: interference foraging competition reflects female reproductive competition in a cooperative mammal

Intense intrasexual competition for breeding opportunities is a characteristic of cooperatively breeding species with high reproductive skew. In such ‘singular’ cooperative breeders, females suffer greater variability in direct reproductive success than do males, and this in turn leads to greater intrasexual competition in females. Under such circumstances, selection should favour traits that enhance female competitive ability, such as size, fighting skill or aggression. However, despite burgeoning interest in female intrasexual competition, there is limited evidence that female cooperative breeders exhibit more pronounced competitive traits than do males. We examined whether intrasexual competition has influenced the expression of a competitive behavioural trait (i.e. prey theft) in a ‘singular’, cooperatively breeding mammal, the dwarf mongoose, Helogale parvula. We used both observational and experimental data to assess whether wild dwarf mongooses exploit interference foraging competition to persecute their reproductive rivals, and whether the sexes differ with regard to this behaviour. We found that nonalpha female mongooses preferentially stole from other females rather than males, and that, under natural foraging conditions, they were more likely to steal prey from their closest rival (i.e. the female immediately below themselves in the dominance hierarchy) than from easier targets much lower in rank. In contrast, male dwarf mongooses (and alpha females) did not exhibit any sex bias, stealing prey indiscriminately from all lower ranking group members. We conclude that the acute intrasexual rivalry suffered by female dwarf mongooses has led to the differential development of this competitive behavioural trait.

Foraging competition in larger groups overrides harassment avoidance benefits in female reindeer (Rangifer tarandus).

Male harassment toward females during the breeding season may have a negative effect on their reproductive success by disturbing their foraging activity, thereby inducing somatic costs. Accordingly, it is predicted that females will choose mates based on their ability to provide protection or will aggregate into large groups to dilute per capita harassment level. Conversely, increasing group size may also lead to a decrease in foraging activity by increasing foraging competition, but this effect has rarely been considered in mating tactic studies. This study examined the importance of two non-exclusive hypotheses in explaining the variations of the female activity budget during the breeding season: the male harassment hypothesis, and the female foraging competition hypothesis. We used focal observations of female activity from known mating groups collected during the breeding season from a long-term (15 years) study on reindeer Rangifer tarandus. We found that females were more disturbed (i.e., spent less time feeding) in the presence of young dominant males, and marginally disturbed in the presence of satellite males, which supports the male harassment hypothesis. We also found that female disturbance level increased with group size, being independent of the adult sex ratio. Consequently, these results rejected the dilution effect, but strongly supported the foraging competition hypothesis. This study therefore highlights a potential conflict in female behaviour. Indeed, any gains from harassment protection were negated by an increase of 6-7 females, since adult males lead larger groups than young males.

Using cross correlations to investigate how chimpanzees (Pan troglodytes) use conspecific gaze cues to extract and exploit information in a foraging competition

In a dyadic informed forager task, chimpanzees (Pan troglodytes) are known to exploit the knowledge of informed subordinates; however, the behavioral mechanisms they employ are unknown. It is tempting to interpret outcome measures, such as which individual obtained the food, in a cognitively richer way than the outcomes may justify. We employed a different approach from prior research, asking how chimpanzees compete by maneuvering around each other, whether they use gaze cues to acquire information from others, and what information they use in moment-to-moment decision-making. We used cross correlations, which plot the correlation between two variables as a function of time, systematically to examine chimpanzee interactions in a series of dyadic informed forager contests. We used cross correlations as a "proof of concept" so as to determine whether the target actions were contingent on, or occurred in a time-locked pattern relative to, the referent actions. A subordinate individual was given privileged knowledge of food location. As expected, an ignorant dominant followed the informed subordinate's movement in the enclosure. The dominant also followed the subordinate's gaze direction: after she looked at the subordinate, she was more likely to gaze toward this same direction within one second. In contrast, the subordinate only occasionally followed the dominant's movement and gaze. The dominant also changed her own direction of movement to converge on the location to which the subordinate directed her gaze and movement. Cross correlation proves an effective technique for charting contingencies in social interactions, an important step in understanding the use of cognition in natural situations.

Does livestock influence the diet of Iberian ibex Capra pyrenaica in the Peneda-Gerês National Park (Portugal)?

We carried out a pilot study about the influence of the domestic goat Capra hircus on the feeding ecology of the Iberian ibex Capra pyrenaica in the Peneda-Gerês National Park (PGNP, Portugal). We mapped the grazing areas of domestic goat flocks and determined their stocking rates in two mountains of PGNP, Gerês and Amarela, and we investigated the diets of both ungulates using fecal microhistology in an area where they partially overlapped during spring and summer. Diet composition, ligneous diversity, and ligneous trophic niche were compared seasonally. Although differences in ligneous components were observed, results revealed a considerable diet overlap mainly due to graminoids consumption, especially during autumn and spring. This suggests that direct or indirect foraging competition between the goat species should not be discarded if they spatially concur. Results also emphasized distinct summer feeding strategies of C. pyrenaica in the area, and the influence of cattle (Bos taurus) and horses (Equus caballus) were hypothesized. We recommend removing feral goats from the mountain environment and monitoring grazing areas of domestic flocks. Estimates of ecological carrying capacity and future diet studies should include cattle, horses, and improvement of herb identification.

Seasonal and specific diet variations in sympatric red and fallow deer of southern Spain: a preliminary approach to feeding behaviour

We studied the diet composition and diet overlap in sympatric red deer (Cervus elaphus hispanicus) and fallow deer (Dama dama) throughout a whole year in order to determine variation due to season, species, sex and age class by analysing rumen contents samples of 81 red and 69 fallow deer shot monthly during 2008–09 in Sierra de Andújar Natural Park, southern Spain. We assessed diet similarity and possible inter- and intra-specific foraging competition. We found different foraging strategies for both species and sexes during constraint periods, and several theoretical considerations of specific interactions and behaviour are discussed with respect to the Mediterranean environment. In both species an annual diet dominated by grasses was recorded, peaking in spring. Browses were an important food resource at the end of winter and at the end of summer, and fruit more in autumn and winter. Red deer ingested a higher proportion of browse than fallow deer, which consumed more acorns and for a longer time showed a better ability to compensate for nutritional constraint periods. An overall decline in diet similarity in summer and at the end of winter led us to assume that exploitative competition between red and fallow deer and even between sexes was probable. Red deer females showed low diet similarity to other deer, while there was a great diet overlap between red deer males and fallow deer females at the end of summer. Differences detected between both two species and sexes do not always support predictions deriving from specific body size and morpho-physiological characteristics, but can probably be explained as a consequence of different metabolic demands. The relationship between plant nutritional attributes and food selection according to reproductive or physiological status and seasonal demands for both sexes and species should be researched in order to perform a better assessment of deer feeding behaviour.

Space, time, and group size: a model of constraints on primate social foraging

Group size is a fundamental aspect of the adaptation of a social animal to its environment. There have thus been numerous attempts to infer optimal group sizes based on both empirical studies of specific taxa and theoretical models that aim to establish generalities. One such generality is that larger groups experience greater within-group foraging competition because of either direct interference by other group members or the rapid exploitation of resources. The ecological constraints hypothesis proposes that increases in group size will increase intragroup feeding competition, thus forcing individuals to visit more patches and to cover greater areas than they would in smaller groups. This paper provides a simple formal model of this constraint, suggesting that two types of constraint limit group sizes in this scenario. First, a constraint on time available to reach an energetic threshold may limit groups to sizes that allow each individual forager to attain that threshold. Second, the balance of foraging costs to benefits may curtail group size even in the absence of a temporal constraint. Both these constraints can be obviated by the adoption of fission–fusion social systems in which a group divides into subgroups during foraging. This latter finding is discussed in relation to primate social systems with an emphasis on time budget approaches.

Foraging competition, vigilance and group size in two species of gregarious antelope

In gregarious species, rates of foraging behaviour are often positively related to group size while there is simultaneously a negative relation between group size and vigilance. Although the mechanisms underlying these behavioural patterns are still incompletely understood, decreased predation risk or increased foraging competition in larger groups have been put forward as two possible explanations. Since most empirical tests of these two hypotheses have used manipulative experiments, they have mainly been limited to small-bodied species or to animals in captivity. Here we suggest a time-budget model to test for the causal effects of predation risk and foraging competition that does not necessitate manipulative approaches. We used this method on two species of gregarious antelope, blesbok (Damaliscus pygargus phillipsi) and impala (Aepyceros melampus). We suggest that increased foraging competition in large groups drives the negative relationship between vigilance and group size in these species. This study shows that observational data can be used to test explicit hypotheses on species that are logistically unsuitable for manipulative experiments, and also render support for hypotheses suggesting that factors unrelated to predation risk are involved in shaping the differences in vigilance rates over different group sizes in gregarious species.

Behavioral Monogamy and Fruit Aavailability in the Large Treeshrew (Tupaia tana) in Sabah, Malaysia

Behavioral monogamy in mammals varies from male–female pairs that spend most of their time in close spatial contact (associated pair-living) to pairs that occupy exclusive territories but travel, forage, and sleep alone (dispersed pair-living). We present radiotelemetry data on 46 adult large treeshrews (Tupaia tana) from 2 populations in Sabah, Malaysia, that indicate that this species forms dispersed pairs across a range of ecological conditions. Dispersed pair-living was the primary behavioral mating system in primary forest during a major fruit masting event, in nonmasting primary forest, and in selectively logged forest with significantly higher fruitfall than in primary forest. Territories of behavioral partners were spatially concordant, but both male and female territories typically overlapped the boundaries of 1–3 extra-pair territories. Comparison between masting and nonmasting forests indicated that females exhibited better body condition during masting, whereas males exhibited larger home-range areas and longer daily movements. Both males and females exhibited better body condition in selectively logged versus primary forests, but ranging patterns were not significantly different between these habitats. We argue that intraspecific foraging competition is the most likely explanation for the evolution of dispersed pair-living in T. tana.

Dietary resource partitioning among sympatric New Zealand and Australian fur seals

Adult male, female and juvenile New Zealand and Australian fur seals Arctocephalus forsteri and A. pusillus doriferus regularly return to colonies, creating the potential for intra- and inter-specific foraging competition in nearby waters. We hypothesise that the fur seals in this study utilise different prey, thereby reducing competition and facilitating coexistence. We analysed scats and regurgitates from adult male, female and juvenile New Zealand fur seals and adult male Aus- tralian fur seals and compared prey remains found in the samples. Most prey consumed by adult male and female fur seals occur over the continental shelf or shelf break, less than 200 km from Cape Gantheaume. Adult female fur seals utilised proportionally more low-energy prey such as large squid and medium-sized fish. The adult female diet reflected that of a generalist predator, dictated by prey abundance and their dependant pups' fasting abilities. In contrast, adult male New Zealand and Aus- tralian fur seals consumed proportionally more energy-rich prey such as large fish or birds, most likely because they could more efficiently access and/or handle such prey. Juvenile fur seals primar- ily consumed small fish that occur in pelagic waters, south of the shelf break, suggesting juveniles cannot efficiently utilise prey where adult fur seals forage. The age and sex groups in this study employ dramatically different strategies to maximise their survival and reproductive success and consequently the prey that they utilise reflect their different physiological constraints and metabolic requirements.

Effects of predation pressure on the cognitive ability of the poeciliid Brachyraphis episcopi

Variable levels of predation pressure are known to have significant impacts on the evolutionary ecology of different populations and can affect life-history traits, behavior, and morphology. To date, no studies have directly investigated the impact of predation pressure on cognitive ability. Here we use a system of replicate rivers, each with sites of high- and low-predation pressure, to investigate how this ecological variable affects learning ability in a tropical poeciliid, Brachyraphis episcopi. We used a spatial task to assess the cognitive ability of eight populations from four independent streams (four high- and four low-predation populations). The fish were required to locate a foraging patch in one of four compartments by utilizing spatial cues. Fish from areas of low-predation pressure had shorter foraging latencies, entered fewer compartments before discovering the reward patch and navigated more actively within the maze, than fish from high-predation sites. The difference in performance is discussed with reference to forage patch predictability, inter- and intraspecific foraging competition, geographic variation in predation pressure, boldness--shyness traits, and brain lateralization. Copyright 2005.