Large Prey Species Research Articles

Food habits and ontogenetic changes in the diet of the sandbar shark, Carcharhinus plumbeus, in Hawaii

The sandbar shark, Carcharhinus plumbeus, is a wide-ranging coastal species in tropical and temperate regions, and it is the most common species of shark in Hawaii, as in many locations where it occurs. Information on the diet and feeding habits of this species in the Pacific Ocean are extremely limited. For this study we quantified the diet of sandbar sharks in Hawaii based on records collected during the Hawaii Cooperative Shark Research and Control Program from 1967 to 1969. During this program a total of 565 stomachs were examined, of which 265 contained food. Sharks ranged in size from 59 to 190 cm total length. Teleosts were the most common prey group, but both cephalopods and crustaceans also occurred frequently. Ontogenetic changes in diet of sandbar sharks were apparent, with crustaceans forming a greater proportion of the diet of smaller sharks. Both cephalopods and elasmobranchs increased in importance with increasing shark size. Prey diversity also increased with size, with large, mobile, and reef prey species found more commonly in the diet of larger sharks. Mature male and female sharks appeared to segregate by depth, though major differences in the diet between the sexes were not apparent. However, there was some evidence of dietary differences between sharks caught in different depths and seasons. The results of this study suggest that sandbar sharks in Hawaii and throughout the world, are primarily piscivores, but also consume a variety of invertebrate prey, and that their diet varies with geographical location and stage of development.

Muscle enzymes reveal walleye (Sander vitreus) are less active when larger prey (cisco,Coregonus artedi) are present

Optimal foraging behaviour in walleye (Sander vitreus) was tested in eight lakes: four containing large prey (cisco, Coregonus artedi) and four without cisco. All eight lakes contained small prey (yellow perch, Perca flavescens). Activity costs and growth potential of walleye were estimated using white muscle enzymes. Anaerobic capacity, measured by lactate dehydrogenase (LDH), increased with walleye size and was lower in lakes with cisco. Aerobic capacity, measured by citrate synthase (CS), decreased with walleye size only in lakes without cisco. Growth potential of walleye, estimated by nucleoside diphosphokinase (NDPK), increased with size only in lakes with cisco. Overall, when cisco were available walleye were less active, able to maintain aerobic capacities, and increased their growth potential as they grew larger. Yellow perch LDH, CS, and NDPK were lower in lakes with cisco. This suggests that yellow perch were less active in lakes where walleye had an alternative large prey species, but yellow perch had higher growth potential when they were the only prey, reflecting the advantage of growth beyond edible sizes. This study reveals that there are physiological benefits for both predators and prey in communities with a wider range of prey sizes.

Prey selection by a reintroduced lion population in the Greater Makalali Conservancy, South Africa

Lion prey selection was studied on the Greater Makalali Conservancy (140 km2), Limpopo Province, South Africa, in order to assist with management strategies. Monitoring was carried out between February 1998 and December 2001. Lion killed 15 species, with warthog, blue wildebeest, Burchell’s zebra, kudu and waterbuck constituting approximately 75% of their diet. Between 2.2% and 3.1% of the available prey biomass was killed yearly, while each female equivalent unit (FEQ) killed between 3 kg and 3.2 kg daily. Lion predation was greater for warthog, wildebeest and waterbuck and less for impala than expected. When male lion were present, a greater number of warthog and giraffe were killed, while number of females had a significant effect on medium sized prey species and total prey species killed. Significantly more warthog, wildebeest and kudu were killed in winter than summer. More prey than expected was killed in open habitats and less than expected in thickets. Managers of small, enclosed reserves need to constantly monitor prey populations, especially medium sized prey and may be able to reduce predation on large prey species by manipulating male lion numbers. Reserves also need to contain adequate open habitats for lion to make use of these areas for hunting.

Performance indices to identify attributes of highway crossing structures facilitating movement of large mammals

Studies assessing the efficacy of wildlife crossing structures often lead to spurious results because of their failure to address masking effects of confounding variables. Confounding variables include variation in human activity, density of crossing structures along the highway corridor, and equality of species' perceived access to each crossing structure. We investigated these issues for wide-ranging large carnivores and their prey species in Banff National Park, Alberta, using data obtained from systematic, year-round monitoring of 13 newly constructed crossing structures for wildlife (underpasses and overpasses) for 34 months post-construction. We standardized the first confounding variable by selecting crossing structures remote from areas of human activity. The second confounding variable we standardized by developing probability models of crossing structure usage assuming habitat homogeneity. We standardized the third confounding variable by developing species-specific, performance indices of crossing structures (=observed through passage usage–expected through passage usage). We regressed the species performance indices against 13 crossing structure variables encompassing structural, landscape, and human activity. Our results suggest that in absence of high human activity structural attributes best explained the performance indices for both large predator and prey species, while landscape and human-related factors were of secondary importance. Crossing structures that were high, wide and short in length strongly influenced passage by grizzly bears Ursus arctos, wolves Canis lupus, elk Cervus elaphus, and deer Odocoileus sp. More constricted crossing structures were favoured by black bears Ursus americanus and cougars Puma concolor. Distance to cover was the most important crossing structure landscape attribute for cougars (negative correlation) and was a significant factor determining passage for grizzly bears, elk and deer (all positive correlations). Our findings underscore the importance of: (a) integrating temporal and spatial variability a priori when addressing the efficacy of crossing structures, and; (b) demonstrate that species respond differently to crossing structure features. In light of these results, we suggest that to maximize connectivity across roads for multiple large mammal species, road construction schemes should include a diversity of crossing structures of mixed size classes. Mitigation planning in a multiple-species ecosystem is likely to be a challenging endeavour and long-term research will aid in the decision-making process.

Counting Tigers

Counting Tigers

Switching effect of predation on global large size prey species exhibiting group defence

The prey–predator model where the prey species exhibits group defence is considered. This mathematical model with one prey species living in two different habitats and a predator where a prey exhibits group defence is studied. The prey species is able to migrate between two different habitats due to change in seasonal conditions. The Routh–Hurwitz stability criteria for a critical point of the system where all species co-exist is investigated. Using rate of conversion of the prey to predator as bifurcation parameter, conditions for a Hopf bifurcation to occur are derived.

Habitat selection and demography of a nonmigratory woodland caribou population in Newfoundland

Several studies have shown that habitat selection and population limitation of woodland caribou (Rangifer tarandus caribou) is typically associated with the interaction among human-induced habitat alteration, wolf predation (Canis lupus), and the availability of alternative prey such as moose (Alces alces) and white-tailed deer (Odocoileus virginianus). Although woodland caribou inhabiting Newfoundland have been exposed to moderate levels of timber harvesting, black bears (Ursus americanus), not wolves, are the principal large predator in this system, and moose represent the alternative large prey species. During a 4-year period of timber harvesting, we monitored the location and status of 24 adults and 46 calves to determine coarse-scale habitat selection and survival rates of a nonmigratory and demographically isolated woodland caribou herd in Newfoundland. We also estimated pregnancy and recruitment rates and determined potential causes of mortality. Habitat selection significantly varied among seasons but was consistent with the hypothesis that caribou avoid habitats where the likelihood of contact with a predator or alternative prey was high. Population growth rate (rs = –0.01 ± 0.06 (mean ± 1SD)), calf recruitment (percentage of 10-month old calves = 13%), and adult survival rate (0.87) indicated that the population was stable. Mean pregnancy rate (96%), parturition date, and the lack of evidence for malnutrition in 22 carcasses suggested that the availability of quality forage is not a key factor limiting population growth. Although predation could not be linked to the death of adult caribou, black bears were responsible for 5 of 15 calf fatalities. This study suggests that black bears need to be considered more seriously as a factor influencing coarse-scale habitat selection and demography in woodland caribou herds.

The community structure of a tropical intertidal mudflat under human exploitation

The impact of human exploitation on the community structure of intertidal mudflats was investigated in an exploited and unexploited control area at Inhaca Island, Mozambique. An increase in the species richness in the exploited area, as expected by the intermediate disturbance hypothesis, was not confirmed. The log body weight–log abundance regression lines were not steeper nor lower, as would be expected if larger species were taken relatively more often. Species diversity was similar in both areas but species composition was significantly different. When the species composition of the five different substrates in each of the two different areas was compared a negative correlation between the total biotic and abiotic stress load and the species diversity appeared. Substrates under a larger total stress load had a lower species diversity, a lower evenness and a higher dominance. A decrease in evenness in exploited areas was expected because of the disappearance of the larger prey species that are exploited by people. Evenness was indeed reduced but this was caused more by the increase of opportunistic species than by the decrease in the abundance of prey species. These findings suggest that intertidal mudflats are more structured through environmental stress factors than through top-down processes, such as competitive exclusion or predation. Human exploitation increased the total stress load of the substrates and thereby affected the species diversity negatively.

DIETARY OVERLAP BETWEEN WOLVES AND COYOTES IN NORTHWESTERN MONTANA

We studied effects of recolonizing wolves (Canis lupus) in the North Fork of the Flathead area of northwestern Montana on the diets of coyotes (C. latrans) from 1994 to 1997. Wolf and coyote diets differed in frequency of occurrence of prey species during 3 of the 4 summers and winters (P < 0.001) during the study. Coyote diets contained more murid prey items, and wolf diets contained more deer (Odocoileus virginianus and O. hemionus) in the summer and elk (Cervus elaphus) in the winter. Coyotes and wolves ate prey of different size during both the summer (P < 0.001) and winter (P < 0.001) months in 1994–1996: wolves took a greater proportion (P < 0.001) of large (>45 kg) prey species and coyotes, small (<2 kg) prey (P < 0.001). Wolves selected a larger proportion of adults (P < 0.001), whereas coyotes selected a larger proportion of juveniles (P < 0.001) during summer. We believe that differential use of food resources facilitates coexistence of wolves and coyotes in the North Fork of the Flathead area.

Prey concealment and spatiotemporal patrolling behaviour of the Indian tree ant Oecophylla smaragdina (Fabricius)

Oecophylla smaragdina workers conceal prey with leaves and twigs on discovering large prey on their ground territory. The prey concealment behaviour occurs concurrently with prey capture and killing. Ants were observed conducting spatiotemporal patrolling around large prey. The garden lizard Calotes versicolor and at least two predatory ant species were found to forage in the same area as O. smaragdina. It is suggested that the prey concealment behaviour of Oecophylla may be a strategy to prevent prey detection by vertebrate predators which use vision to prey on similar large prey species.

Diet choice and capture success of wild dog (Lycaon pictus) in Hluhluwe‐Umfolozi Park, South Africa

AbstractThe small population of wild dog Lycaon pictus (n= 3 to 30) in Hluhluwe‐Umfolozi Park (HUP) has declined since 1992. The survival of dogs in HUP is dependent on the reintroduction of more dogs; however, wild dog reintroduction programmes are fraught with problems and many have failed. In this paper the diet and capture success of the wild dog pack in the Hluhluwe Section, and the influence of dietary considerations on the success of the future reintroduction of wild dogs in this reserve, are investigated. Diet choice was determined from scat analysis, personal observation and field staff records. Eight ungulate prey species were identified from scat analysis: nyala Tragelaphus angasi and impala Aepyceros melampus were the most abundant ungulate species in HUP and accounted for 77% of the diet. On the whole, wild dogs included prey types in the diet consistent with a rate‐maximizing foraging approach, although some prey were clearly taken opportunistically. The dogs preyed mostly on small‐ (&gt; 25 kg) to medium‐sized (40–90 kg) prey, while the young of large (&lt; 90 kg) prey species or scavenged carcasses supplemented the diet during the dry season. Adult nyala were taken more frequently than other age classes, but wild dog preyed on juvenile impala more than expected. Female prey were taken more frequently than males but selection did not differ from prey population sex ratios. Prey capture success was similar to that of previous studies from both open and densely wooded habitats and the wild dogs successfully caught 48% of all prey species pursued. Results suggest that wild dogs are quite capable of adapting both their diet choice and foraging technique to the dense vegetation in HUP. We conclude that prey type, prey availability and habitat constraints on prey capture success, will not affect the reintroduction of more wild dogs into HUP.

Foraging dynamics of lions in a semi-arid environment

Direct observations on the foraging activities of lions, based on 920 attempts to capture prey and 156 kills, on the plains of Etosha National Park, Namibia, revealed a regular nocturnal pattern of mostly coordinated group hunting. Lions scavenged rarely and killed mainly prey animals weighing less than 50 kg, which contributed to 73% of the observed kills and 50% of the estimated biomass consumed. Capture success increased with lion group size and was also greater during coordinated group hunts. Lions hunted most of the prey that they encountered, showing a preference for large prey species. Average food acquisition ranged from 8.7 kg/day per lioness in the dry season to 14 kg/day per lioness in the wet season. During the dry season, coordinated cooperative hunting was essential and lionesses most often formed groups of 2, thereby acquiring higher daily food intake than groups of other sizes. In the wet season, lioness groups of all sizes obtained more than the estimated daily requirements, and lionesses did not uniformly forage in the smaller groups capable of greater food acquisition.

Prey Consumption by Larvae of Tetanocera ferruginea (Diptera: Sciomyzidae) in Relation to Number of Snail Prey Species Available

The foraging strategies of predatory Tetanocera ferruginea Fallen larvae change as the diversity of available prey-snail species increases. When prey species diversity increased from one to four, T. ferruginea larvae ate an average of 34.6 versus 19.9 prey, respectively. Length of time required for T. ferruginea to complete larval development was significantly longer when one species of snail was available (22 d) compared with four (19 d). Increasing prey species diversity resulted in significantly greater quantities of snail biomass being eaten (248.4 mg of snails eaten when only one species was present compared with 334.0 mg when four species were present). These patterns resulted from larvae choosing a few larger prey species rather than many small prey, thus maximizing their energy accumulation and minimizing foraging time.

Assessing the Diet of Dingoes from Feces: A Comparison of 3 Methods

I assessed diet of the dingo (Canis familiaris dingo) from 2,495 fecal samples using frequency of occurrence of prey types, relative weight of remains of prey types, and biomass of ingested prey types. There were no significant differences between methods in ranking prey types provided that _70 fecal samples/ month were analyzed. The widely used frequency method that is used to understand what and relatively how much is eaten is justified in diet studies of dingoes and other carnivores. Only the biomass ingested method allows an evaluation of the biomass or numbers of particular prey species that are eaten. For dingoes, and probably also for other carnivores, objective adjustments need to be applied to account for differences in size between juvenile and adult large prey species and for differences in the proportion of each age class

Predation by Didinium Nasutum: Effects of Predator and Prey Size

Experimental manipulation of the size of Didinium nasutum, a protozoan predator, feeding on large and small Paramecium species was used to examine the effects of predator and prey size on predator behavior and capture success. Didinum size is a function of prey size; large and small Didinium were obtained by conditioning predators on large or small prey species prior to experimentation. The predatory behavior of large and small predators feeding on large and small prey was monitored through an entire division cycle. Large Didinium had shorter handling times and encounter times on both sizes of prey than small Didinium. Large Didinium made more captures per division on either size of prey. Large prey required longer handling times, longer engulfing times, and were encountered more frequently than small prey for both sizes of predator. First captures were more difficult than subsequent captures for all predators. Small predators were more successful initially in capturing small prey than were large predators; first captures by large predators on small prey were particularly difficult. Encounter times, the number of encounters per capture, capture times, and handling times varied with the size of the predator and also varied within the division cycle of the predator. The effect of time within the division cycle may be due to increasing size as prey are captured and/or to adaptations to the specific prey species following initial captures. Didinium may adapt to new prey species through morphological changes in the oral apparatus, chemoreceptors, or extrusive organelles, in addition to shifts in size. That each size of Didinium had more successes per encounter on the size of prey to which it had been conditioned suggests that the size shift improves that aspect of the predatory behavior. However, other aspects (such as handling time and time to each encounter) show a clear advantage to large size. Large size also improves survival ability of Didinium under conditions of starvation (Hewett 1987). For large predators to maintain a large size on small prey would require a substantial increase in the division time. Selection forces favoring fast division rates, may impose restraints, making the size of Didinium on any prey species a compromise.

Predatory feeding behavior of the marine cyclopoid copepod Corycaeus anglicus

Feeding rates, patterns of prey selection, and starvation tolerance were investigated for adult males and females of the cyclopoid copepod Corycaeus anglicus collected from the waters of Friday Harbor, Washington, USA. Selection by C. anglicus was determined largely by prey body-size, but was also affected by species and developmental stage. Small developmental stages of all prey species were fed upon at relatively low rates. The small calanoid species Acartia clausii was increasingly vulnerable to predation by C. anglicus as it progressed through successive developmental stages. Larger prey species, Pseudocalanus sp. and Calanus pacificus, were more vulnerable in intermediate stages, the C3 and N6 stages, respectively. Larger and smaller prey were characteristically attacked at different sites on their bodies; however, attack sites fell within a similar range of body widths, 130 to 170 μm. Males of Corycaeus anglicus killed a maximum of 1.4 prey d-1 when feeding on the optimally-sized adult females of Acartia clausii, which are approximately equivalent to its own body length. Males fed at approximately double the rates of females. Despite its small size and apparent lack of metabolic stores, this cyclopoid is highly tolerant of starvation conditions. Median survival time without food is at least 2 wk for both males and females. In its predatory behavior, C. anglicus employs an ambush-type strategy and seems to be adapted for infrequent encounters with relatively large prey.

The Ecology of the Dingo in North-Eastern New South Wales. 2. Diet.

The diet of two populations of dingoes, from adjacent areas different in topography and altitude, from 1969 to 1974, were similar. The remains of native mammals were found in over 90% of the scats, and Wallabia bicolor was the most important single prey species in both areas. The high frequency of large native species in this and other studies of dingoes' diet suggested that dingoes may be essentially predators of the larger native species. The mammalian composition of the diet varied significantly between May-October and November-April; this reflected a change in the hunting strategy ofthe dingo, as an outcome of behavioural necessity rather than a change in the relative abundances of prey species. Concurrent with an increase in the dingo population, the composition of the diet changed between 1972 and 1974, with an increased concentration on larger prey species in the later years; this also indicated a change in hunting strategy. Large prey species provide potentially more biomass per unit kill; and this change in hunting strategy may be a behavioural mechanism for buffering dingo populations against either increases in their own population or decreases in those of their prey.

A field study of prey selection in planktivorous fish larvae.

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.

The Effect of Prey Size on the Functional and Numerical Responses of a Protozoan Predator to Its Prey

The functional response of Didinium nasutum to variation in density of three Paramecium species was found to decrease with increasing prey size. The attack coefficient is similar on small and intermediate—sized Paramecium and declines sharply on the largest prey species. Handling time increases with increasing prey size. Actual division rates of the predator are highest, however, on the intermediate—sized prey and lowest on the smallest prey species. This suggest that there is an optimal Paramecium size at which Didinium division rates are highest. The density of prey and the size of prey were also found to have a significant effect on the volume of the Didinium cells. It is suggested that there may be contrasting advantages to Didinium of being of as large a size as possible and of dividing as quickly as possible.

FEEDING OFNEOMYSIS MERCEDIS(HOLMES)

The diet of the opossum shrimp, Neomysis mercedis, in the Sacramento River Estuary was studied in relation to food availability, i.e., plankton, from January through November, 1976. The composition of the diet of N. mercedis varied in relation to mysid size and prey availability. Mysids exhibited strong positive selection for the large diatom prey species while "avoiding" small diatom prey. Although diatoms were the most abundant prey identified from the guts of specimens of N. mercedis it was determined that predation on rotifers and copepods accounted for > 80% of the energy consumed by other-than-juvenile mysids (≥7 mm in length). Juvenile mysids (≤ 3 mm in length) ingested rotifers when rotifers were abundant but were not found to consume copepods. Laboratory feeding experiments indicate a density-dependent feeding by N. mercedis on copepods, i.e., as copepod density increases mysid predation on copepods also increases. Feeding observations indicate that N. mercedis is not a particularly active predator, capturing prey drawn into its feeding current but not actively pursuing prey. N. mercedis appears to feed continuously, with a peak in activity for mature mysids during darkness, a pattern not apparent in immature mysids. Consumption of the detritus was not considered significant. Although herbivory may be of direct importance during the spring diatom increase, carnivory was the major source of energy for N. mercedis in the Sacramento River during 1976.