The food, feeding habits and feeding structures of the whiting species Sillago sihama (Forsskål) and Sillago analis Whitley from Townsville, North Queensland, Australia

The diet, feeding habits and feeding structures of 519 Sillago sihama and 493 S. analis specimens collected from beaches and estuaries in the Townsville region are described. The species are carnivores on a wide range of benthic, epibenthic and planktonic prey. Both undergo size related dietary shifts; S. sihama from predominantly planktonic crustaceans in fish of less than 80 mm t.l . to polychaetes, penaeid and brachyuran crustaceans and molluscs at larger sizes; S. analis from a mixture of small Mesodesma eltanae and amphipods at sizes of less than 80 mm t.l . to predominantly M. eltanae and small quantities of penaeids and brachyuran crabs in larger fish. The dietary shift was not associated with migration from a nursery area.
While the species showed considerable overlap in the types of prey utilized, there were significant differences in the relative importance of shared components in their diets. The major difference was in the relative importance of the bivalve mollusc, M. eltanae. This was the dominant food of S. analis but of secondary importance in S. sihama. Associated with this basic difference in diet was a specialization of the pharyngeal dentition in S. analis to molariform crushing plates and a reduction of the gill rakers to vestigial knobs. In S. sihama , the pharyngeal teeth are sharp and pointed and the gill rakers normal.
The feeding activity of S. analis , but not S. sihama , is limited by the tidal cycle, a factor which may be a form of temporal partitioning.     

Within-colony feeding selectivity by a corallivorous reef fish: foraging to maximize reward?

Foraging theory predicts that individuals should choose a prey that maximizes energy rewards relative to the energy expended to access, capture, and consume the prey. However, the relative roles of differences in the nutritive value of foods and costs associated with differences in prey accessibility are not always clear. Coral‐feeding fishes are known to be highly selective feeders on particular coral genera or species and even different parts of individual coral colonies. The absence of strong correlations between the nutritional value of corals and prey preferences suggests other factors such as polyp accessibility may be important. Here, we investigated within‐colony feeding selectivity by the corallivorous filefish, Oxymonacanthus longirostris, and if prey accessibility determines foraging patterns. After confirming that this fish primarily feeds on coral polyps, we examined whether fish show a preference for different parts of a common branching coral, Acropora nobilis, both in the field and in the laboratory experiments with simulated corals. We then experimentally tested whether nonuniform patterns of feeding on preferred coral species reflect structural differences between polyps. We found that O. longirostris exhibits nonuniform patterns of foraging in the field, selectively feeding midway along branches. On simulated corals, fish replicated this pattern when food accessibility was equal along the branch. However, when food access varied, fish consistently modified their foraging behavior, preferring to feed where food was most accessible. When foraging patterns were compared with coral morphology, fish preferred larger polyps and less skeletal protection. Our results highlight that patterns of interspecific and intraspecific selectivity can reflect coral morphology, with fish preferring corals or parts of coral colonies with structural characteristics that increase prey accessibility.     

A field study of prey selection in planktivorous fish larvae

Summary The food selection of larval fish was studied from field samples collected in two areas that differ in productivity. In the area where planktonic primary and secondary production was high the fish larvae showed a tendency to specialise and they selected the largest prey species available as food; in the area of lower production fish were generalists and they fed equally on all size classes.Abundance of prey was found to be one of the decisive factors in the prey selection of planktivorous fish larvae. Large prey species (calanoids) were selected when their absolute abundance was high but when their abundance was low, small-sized cladocerans were preferred. Visibility and stage of life history were also assumed to affect the mode of selection.     

Prey selectivity affects reproductive success of a corallivorous reef fish

Most animals consume a narrower range of food resources than is potentially available in the environment, but the underlying basis for these preferences is often poorly understood. Foraging theory predicts that prey selection should represent a trade-off between prey preferences based on nutritional value and prey availability. That is, species should consume preferred prey when available, but select less preferred prey when preferred prey is rare. We employed both field observation and laboratory experiments to examine the relationship between prey selection and preferences in the obligate coral-feeding filefish, Oxymonacanthus longirostris. To determine the drivers of prey selection, we experimentally established prey preferences in choice arenas and tested the consequences of prey preferences for key fitness-related parameters. Field studies showed that individuals fed almost exclusively on live corals from the genus Acropora. While diet was dominated by the most abundant species, Acropora nobilis, fish appeared to preferentially select rarer acroporids, such as A. millepora and A. hyacinthus. Prey choice experiments confirmed strong preferences for these corals, suggesting that field consumption is constrained by availability. In a longer-term feeding experiment, reproductive pairs fed on non-preferred corals exhibited dramatic reductions to body weight, and in hepatic and gonad condition, compared with those fed preferred corals. The majority of pairs fed preferred corals spawned frequently, while no spawning was observed for any pairs fed a non-preferred species of coral. These experiments suggest that fish distinguish between available corals based on their intrinsic value as prey, that reproductive success is dependent on the presence of particular coral species, and that differential loss of preferred corals could have serious consequences for the population success of these dietary specialists.     

Damage released prey alarm substances or predator odours? Risk assessment by an aquatic oligochaete

Although the abilities of prey to detect and respond to chemical substances associated with a predator have been widely reported, the factors promoting the evolution of responses to prey alarm cues vs. predator odours are still vague. In this article, we combined field research with laboratory experiments to explore which chemical substance associated with predator activity (predator odour, conspecific or heterospecific alarm substances) induces defence responses in the aquatic oligochaete Stylaria lacustris, which is vulnerable to common littoral predators. The field results indicated that predators injure the oligochaetes and a great proportion, up to 45% of individuals in the population, were found to be damaged. The results of the laboratory experiments revealed that chemical odours from damselfly larvae feeding on S. lacustris did not induce the defence response in the oligochaetes. On the contrary, oligochaetes detected and responded to alarm substances from damaged conspecifics alone and substances from damaged cladoceran Daphnia magna. We discussed conditions favouring the responses to damage released prey alarm cues instead of predator odours in Stylaria lacustris. Our data suggest that the selection of responses to alarm cues from damaged prey vs. predator odours may be dependent on three factors: (1) non-species-specific predation, (2) divergence of food niche of the different stages of the predator and (3) complex food web with multiple predators. Handling editor: S. Declerk     

New Essential Aphid Prey for Anatis ocellata and Calvia quatuordecimguttata (Coleoptera: Coccinellidae)

Seven aphid species (Eucalipterus tiliae, Tuberculatus annulatus, Euceraphis betulae, Cavariella konoi, Acyrthosiphon ignotum, A. pisum, Macrosiphoniella artemisiae) were tested as prey for larvae of Anatis ocellata and all were essential prey. Nine aphid species (Chaitophorus tremulae, Cavariella konoi, Aphis farinosa, Eucalipterus tiliae, Euceraphis betulae, Macrosiphoniella artemisiae, Acyrthosiphon ignotum, Aphis spiraephaga, Aphis fabae) were tested as prey for Calvia quatuordecimguttata. The former six species were 'essential' food, while the latter three aphid species were unsuitable food for C. quatuordecimguttata. The experiments were conducted under laboratory conditions with no choice of prey. Some of the checked 'essential' prey apparently do not represent food in the field as they occur in other habitats than the studied coccinellid species that are common on trees.     

Diet and prey selection of six species of tuna baitfish in three coral reef lagoons in the Solomon Islands

The diets and prey selection of six species of tuna baitfish (the engraulids Stolephorus devisi and S. heterolobus, three dussumierids of genus Spratelloides, and the apogonid Archamiazosterophora. were examined at two heavily fished and one unfished site in the Solomon Islands. All species ate almost exclusively nektonic zooplankton, especially crustaceans. Calanoid copepods were the most importantpreyofallspeciesexcept A. zosterophora, whichateagreater biomassoflarvalfish. Baitfishcould be divided into two groups according to prey taxa: the apogonid A. zosterophora and the engraulids S. devisi and S. heterolobus ate similar prey in similar proportions; the three dussumierid species (Spratelloides) ate smaller zooplankton and a greater proportion of calanoids than the other species. The size of prey eaten differed greatly between baitfish species. A. zosterophora ate larger prey than other species. The two Stolephorus species ate similar-size prey, which were larger than the prey of the three species of Spratelloides. Among the Spratelloides, S. delicatulus ate smaller prey than the other two species. All species differed in the size of calanoids, carids and brachyurans they ate. In all cases, prey differed more by the minimum dimension (width) than by volume. There were significant relationships between fish length and prey width and volume, except for Archamia. However, in terms ofvolume, the prey of Stolephorus increased with fish size at a much greater rate than in Spratelloides species. Baitfish diets were compared to the zooplankton available. Prey selection by the three Spratelloides species and two Sfolephorus species was density-dependent for all common prey types, although Stolephorus positively selected hyperiid amphipods and brachyurans. Archamia showed strong negative selection for calanoids and selected larger zooplankters, including fish larvae and carids, avoiding smaller, more common, prey. Overall baitfish density and zooplankton density did not correlate at either of the heavily fished sites. Nor were there consistent differences for any species in diet or changes in prey selection between the heavily fished and unfished sites. This suggests that, in these lagoons, commercial baitfish catches are not directly influenced by the composition or density of prey.     

Food selection by bacterivorous protists: insight from the analysis of the food vacuole content by means of fluorescence in situ hybridization

A modified fluorescence in situ hybridization (FISH) method was used to analyze bacterial prey composition in protistan food vacuoles in both laboratory and natural populations. Under laboratory conditions, we exposed two bacterial strains (affiliated with beta- and gamma-Proteobacteria -- Aeromonas hydrophila and Pseudomonas fluorescens, respectively) to grazing by three protists: the flagellates Bodo saltans and Goniomonas sp., and the ciliate Cyclidium glaucoma. Both flagellate species preferably ingested A. hydrophila over P. fluorescens, while C. glaucoma showed no clear preferences. Differences were found in the digestion of bacterial prey with B. saltans digesting significantly faster P. fluorescens compared to two other protists. The field study was conducted in a reservoir as part of a larger experiment. We monitored changes in the bacterial prey composition available compared to the bacteria ingested in flagellate food vacuoles. Bacteria detected by probe HGC69a (Actinobacteria) and R-BT065 were negatively selected by flagellates. Bacteria detected by probe CF319a were initially positively selected but along with a temporal shift in bacterial cell size, this trend changed to negative selection during the experiment. Overall, our analysis of protistan food vacuole content indicated marked effects of flagellate prey selectivity on bacterioplankton community composition.     

Sexual Dimorphism of Head Size in Phrynocephalus przewalskii: Testing the Food Niche Divergence Hypothesis

Sexual size dimorphism （SSD） is a general phenomenon in lizards, and can evolve through sexual selection or natural selection. But natural selection, which was thought to operate mainly through reducing the competition be- tween the two sexes （niche divergence hypothesis）, gave rise to a lot of controversy. We tested the niche divergence hypothesis in the toad-headed lizard Phrynocephalus przewalskii by comparing diet composition and prey sizes between males and females. The species was found to be sexual dimorphic, with males having relatively larger snout-vent length, head width, head length, and tail length, while females have relatively larger abdomen length. Based on analysis of 93 studied stomachs, a total of 1359 prey items were identified. The most common prey items were formicid, lygaeid and tenebrionid. The two sexes did not differ in the relative proportions of prey size categories they consumed and the dietary overlap based on prey species was high （O = 0.989）. In addition, the meal size, the volume or any maximal dimension of the largest prey item in the stomach was not explained by the sexes. According to our results, food niche divergence might not play an important role in the SSD evolution ofP. przewalskii.     

The dynamics of top-down and bottom-up effects in food webs of varying prey diversity, composition, and productivity

Prey diversity is thought to mediate the strength of top-down and bottom-up effects, but few experiments directly test this hypothesis. I assembled food webs of bacteria and bacterivorous protist prey in laboratory microcosms with all combinations of five productivity levels, two top predator treatments (present or absent), and three prey compositions. Depauperate food chains contained one of two edible prey species, while more diverse food webs contained both edible prey species plus two additional less-edible/inedible prey. Equilibrium theory predicts that prey diversity should weaken the top-down and bottom-up effects on trophic level biomasses, due to density compensation among prey species. Top-down effects should increase with productivity in food chains, but decrease with productivity in food webs. Results revealed highly dynamic top-down effects, the strength of which varied more over time than among treatments. Further, top-down effects did not merely vary in absolute strength over time, but also in relative strength across different prey compositions and productivity levels. It might be expected that equilibrium models would qualitatively reproduce time-averaged results. However, time-averaged data largely failed to support equilibrium predictions. This failure may reflect strong temporal variability in treatment effects combined with nonlinear density dependence of species' per-capita growth rates. Strong temporal variability in the strength of top-down effects has not previously been demonstrated, but likely is common in nature as well.     

Prey Selection by the Lady Beetle Harmonia axyridis: The Influence of Prey Mobility and Prey Species

The influence of prey mobility and species on prey selection by the coccinellid Harmonia axyridis Pallas was determined under laboratory conditions for two prey species, Hyaliodes vitripennis (Say) and Tetranychus urticae Koch. Prey selection was influenced by prey mobility. In the presence of active prey, the coccinellid selected T. urticae while in presence of immobilized prey, H. vitripennis was preferred. Harmonia axyridis searching time was longer in the presence of active H. vitripennis than in the presence of active T. urticae. Moreover, the coccinellid capture rate was lower for active H. vitripennis caused by effective defensive mechanisms. Prey suitability was affected by prey mobility and species. Immobilized H. vitripennis were the most profitable prey, i.e. induced a shorter developmental time and no mortality. However, active H. vitripennis were not a suitable food source for H. axyridis. Our results suggested that three factors are involved in prey selection by H. axyridis: (i) prey mobility; (ii) prey defensive mechanisms; and (iii) prey species.     

Food selectivity versus prey availability: a study using the marine fish Pomatoschistus microps

Summary The food selection of the common goby, Pomatoschistus microps Krøyer, was studied in the field and in laboratory experiments on the Swedish west coast. The three most important prey organisms for P. microps in the study area were Corophium volutator, chironomid larvae and Nereis spp. Corophium was consumed more than any other prey, even when it was not the most abundant prey species in the bottom. One reason may be the higher activity of Corophium above the sediment surface, which may increase its visibility and consequently its vulnerability to visual predators. When P. microps was offered Corophium and chironomid larvae with similar exposure in laboratory experiments, it showed no preference for either of the prey items. It always took the closest mobile prey, regardless of species and size.     

云南星云湖长臀云南鳅两性异形及其生境适应性

云南鳅属鱼类是云贵高原及邻近区域特有鱼类,其独特两性异形现象可能是对喀斯特高原特定生境的一种重要适应。本文对云南星云湖特有鱼类长臀云南鳅两性异形、个体繁殖力及与之关联的雌雄摄食分化问题进行了研究,以揭示其两性异形特征并探讨其与生境的关系。结果表明: 长臀云南鳅两性异形指数为0.23,表明它是偏向于雌性体型较大的两性异形类型。同时,雌雄外部形态存在明显的色斑差异,雌鱼体侧密布横向色斑,而雄鱼体侧则有一明显的纵向条纹,横向色斑稀少或缺乏。单因素方差分析、主成分分析、判别分析及单因素相似性分析(ANOSIM)等进一步证实长臀云南鳅雌雄形态性状明显分离,全长、叉长、体长、头宽/头长、腹鳍起点-胸鳍起点(JK)/体长等对两性形态差异起主导作用。雌鱼繁殖力为(1364.5±489.3)粒,变化幅度为470~2430粒,其繁殖力随体长的增长而增大。食物分析显示,长臀云南鳅以摇蚊幼虫、蜉蝣稚虫为主要食物,食性较为狭窄。雌雄长臀云南鳅食物组成较为相似,但两者具有统计学意义上的显著差异。繁殖力选择压力、食物分化等可能对星云湖长臀云南鳅两性异形的形成起重要驱动作用,而两性异形的出现是长臀云南鳅对喀斯特贫营养龙潭生境的一种重要适应。     

Free‐living nematodes as prey for higher trophic levels of forest soil food webs

Nematodes are the most abundant invertebrates in soils and are key prey in soil food webs. Uncovering their contribution to predator nutrition is essential for understanding the structure of soil food webs and the way energy channels through soil systems. Molecular gut content analysis of consumers of nematodes, such as soil microarthropods, using specific DNA markers is a novel approach for studying predator–prey interactions in soil. We designed new specific primer pairs (partial 18S rDNA) for individual soil‐living bacterial‐feeding nematode taxa (Acrobeloides buetschlii, Panagrellus redivivus, Plectus velox and Plectus minimus). Primer specificity was tested against more than 100 non‐target soil organisms. Further, we determined how long nematode DNA can be traced in the gut of predators. Potential predators were identified in laboratory experiments including nine soil mite (Oribatida, Gamasina and Uropodina) and ten springtail species (Collembola). Finally, the approach was tested under field conditions by analyzing five mite and three collembola species for feeding on the three target nematode species. The results proved the three primer sets to specifically amplify DNA of the respective nematode taxa. Detection time of nematode DNA in predators varied with time of prey exposure. Further, consumption of nematodes in the laboratory varied with microarthropod species. Our field study is the first definitive proof that free‐living nematodes are important prey for a wide range of soil microarthropods including those commonly regarded as detritivores. Overall, the results highlight the eminent role of nematodes as prey in soil food webs and for channelling bacterial carbon to higher trophic levels.     

Diets and habitat preferences of three species of crocidurine shrews in arid southern Africa

The diets and habitat preferences of three species of crocidurine shrews, Crocidura cyanea, C. fuscomurina , and C. hirta (Insectivora: Soricidae), were studied in arid areas of Namibia in March and April, 1992. Simultaneous sampling of the prey ingested and available along foraging trails showed that, although the shrews are generalist insectivores that take most types of prey from the range available, each species selected Araneida, Chilopoda, Isoptera, and insect larvae but avoided Formicidae. The preferred prey were mostly soft-bodied with a relatively high ratio of body water to energy content, which may assist in maintenance of body water balance. The three species showed inconsistent preferences for rarer categories of prey such as Thysanura and Orthoptera, as well as for Coleoptera. Each species of shrew selected sites providing dense ground level vegetation and deep leaf litter, With the preference for cover being strongest in C. fuscomurina. Dense vegetation probably provides shelter from predators and high daytime temperatures; both C. fuscomurina and C. hirta used denser vegetation by day than by night. Each species foraged in leaf litter, perhaps increasing access to preferred types of prey. Preference for moist soil, especially in C. fuscomurina , probably also reflects increased access to preferred prey, although moist soil may also facilitate burrow construction. Because patterns of habitat and diet selection appear to be linked, future research on resource use in these shrews should be pursued most fruitfully in field experiments or captive laboratory trials.     

Diel and density-related changes in food consumption and prey selection by brook charr in a New Hampshire stream

Synopsis We report the results of a field study testing influences of both density and changes over the diel cycle on food consumption and prey selection by brook charr,Salvelinus fontinalis. Charr density in replicate 35 m long sections of a New Hampshire stream was adjusted to either medium or high levels (relative to natural densities). Diets of charr and the availability of drifting prey were then sampled every four hours for 24 hours. There were no significant diel changes in the weight of prey consumed by charr per four hours, though there was some indication of reduced feeding at night. Chary fed selectively on different prey taxa, showing most preference for cased caddis larvae. Several species of mayflies and stoneflies were selected more strongly during the day than at night. Charr fed selectively on larger prey during the daytime but showed no size-selection at night. The density of charr had no significant effects on either their rate of food consumption or on selection for prey of different taxa or sizes.     

Community-wide character displacement in New Zealand skinks

Aim  To test for community-wide character displacement in New Zealand skinks.
Location  Four small islands in the New Zealand archipelago.
Methods  (1) We conducted a field experiment on a single island to evaluate whether prey size selection is correlated with lizard body size. We pitfall trapped 69 skinks from three species, measured several aspects of their morphology and presented each animal with a variety of different-sized prey in a food choice experiment. (2) We tested whether the morphological characteristics associated with prey size selection were evenly partitioned in four island skink communities using null models.
Results  Prey size selection was associated with skink morphology; larger skinks consumed larger prey. Null model analyses showed support for evenly displaced body sizes on one island, weak support on one island and no support on two islands.
Main conclusions  Results showed mixed support for community-wide character displacement in New Zealand skinks. Differences in body sizes appear to reflect the use of different-sized prey. Even differentiation in body sizes on one island suggests that species coexistence is facilitated by interspecific differences in prey size selection. However, little support was found on other islands, suggesting that other factors, such as interspecific differences in habitat selection and/or diurnal activity patterns, may interact with differences in prey size selection to promote coexistence among New Zealand skinks.     

Detecting In Situ Copepod Diet Diversity Using Molecular Technique: Development of a Copepod/Symbiotic Ciliate-Excluding Eukaryote-Inclusive PCR Protocol

Knowledge of in situ copepod diet diversity is crucial for accurately describing pelagic food web structure but is challenging to achieve due to lack of an easily applicable methodology. To enable analysis with whole copepod-derived DNAs, we developed a copepod-excluding 18S rDNA-based PCR protocol. Although it is effective in depressing amplification of copepod 18S rDNA, its applicability to detect diverse eukaryotes in both mono- and mixed-species has not been demonstrated. Besides, the protocol suffers from the problem that sequences from symbiotic ciliates are overrepresented in the retrieved 18S rDNA libraries. In this study, we designed a blocking primer to make a combined primer set (copepod/symbiotic ciliate-excluding eukaryote-common: CEEC) to depress PCR amplification of symbiotic ciliate sequences while maximizing the range of eukaryotes amplified. We firstly examined the specificity and efficacy of CEEC by PCR-amplifying DNAs from 16 copepod species, 37 representative organisms that are potential prey of copepods and a natural microplankton sample, and then evaluated the efficiency in reconstructing diet composition by detecting the food of both lab-reared and field-collected copepods. Our results showed that the CEEC primer set can successfully amplify 18S rDNA from a wide range of isolated species and mixed-species samples while depressing amplification of that from copepod and targeted symbiotic ciliate, indicating the universality of CEEC in specifically detecting prey of copepods. All the predetermined food offered to copepods in the laboratory were successfully retrieved, suggesting that the CEEC-based protocol can accurately reconstruct the diets of copepods without interference of copepods and their associated ciliates present in the DNA samples. Our initial application to analyzing the food composition of field-collected copepods uncovered diverse prey species, including those currently known, and those that are unsuspected, as copepod prey. While testing is required, this protocol provides a useful strategy for depicting in situ dietary composition of copepods.     

STOMACH CONTENTS OF LONG-FINNED PILOT WHALES (GLOBICEPHALA MELAS) STRANDED ON THE U.S. MID-ATLANTIC COAST

Ten prey taxa were recorded from the stomach contents of eight long-finned pilot whales ( Globicepbala melas ) independently stranded along the U.S. mid-Atlantic coast. Relative importance of prey species was determined by methods that incorporate prey frequencies of occurrence, proportions of numerical abundance, and proportions of reconstructed mass. Separate analyses of trace (free, durable body parts representing well-digested prey items) and non-trace (relatively intact prey specimens) food material were conducted in order to address biases caused by differential rates of digestion and passage through the gastrointestinal tract. Different measures of prey importance yielded varying results, but the long-finned squid ( Loligo pealei ) was the most important prey species regardless of how prey importance was defined. Fishes were relatively unimportant in the diet. Our results indicate that the diets of western North Atlantic long-finned pilot whales differ substantially from what has been previously reported in the literature and that results from food-habits studies that utilize different techniques may not be comparable.     

Changing vulnerability to predation related to season and sex in an African ungulate assemblage

The consequences of predation for prey population dynamics depend on the extent to which this mortality is predisposed by malnutrition or senescence, or additive in the sense that animals that would otherwise not have died at that time were killed. In places lacking effective predators, few adult ungulates die during the summer or wet season months when food is plentifully available. Hence the seasonal distribution of predator kills as well as the age and sex classes of the prey indicates the extent to which malnutrition contributes to mortality as well as other influences on vulnerability. Using records of animal deaths assembled over 35 years in South Africa's Kruger National Park, these patterns were investigated for 12 ungulate species forming the prey of lions, and for three other large predators with respect to one prey species. Buffalo, kudu and giraffe were more strongly represented in kills made during the late dry season, while wildebeest and zebra made relatively greater contributions during the wet season. Impala, waterbuck, warthog and rarer antelope species became more prominent in kills during transitional periods between seasons. Five prey species showed an elevation in representation of males in lion kills during the mating season, as well as impala for all predator species. Females were more prominently represented in kills during the time of late gestation and parturition for three prey species. Hence reproductive activities as well as changing vegetation cover and food resources affected vulnerability to predation. Shifts in susceptibility to predation over the seasonal cycle corresponded with rainfall‐related variation in the annual representation of these ungulate species in lion kills. The availability of vulnerable prey species, age and sex classes at different stages of the seasonal cycle helps maintain a high abundance of lions. These factors contribute to the strong additive impact that predation has had on the abundance of some of these ungulate populations.