Low Prey Availability Research Articles

Jaguars, pumas, their prey base, and cattle ranching: ecological interpretations of a management problem

Jaguar and puma depredation on livestock may be influenced by (1) innate and learned behavior; (2) health and status of individual cats; (3) division of space and resources among jaguar and puma; (4) cattle husbandry practices; and (5) abundance and distribution of natural prey. Our study in Los Llanos of Venezuela aimed to establish how all these elements related to cattle being lost to cat depredation. Prey distribution was influenced by forest composition, topographical characteristics, and degree of habitat interspersion. The biomass of natural prey in the study area was adequate to support the resident large cats without a subsidy of livestock. Selective rather than opportunistic hunting by the cats reinforced that conclusion. Puma were responsible for more attacks on livestock than jaguar, frequently in maternity pastures in upland areas of relatively low prey availability. Management recommendations are discussed that may be relevant to other savanna/forest mosaics of South America.

Feeding of diving predators and diel vertical migration of prey: King penguin diet versus trawl sampling at Kerguelen Islands

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 227:51-61 (2002) - doi:10.3354/meps227051 Feeding of diving predators and diel vertical migration of prey: King penguins¹ diet versus trawl sampling at Kerguelen Islands C. A. Bost1,*, T. Zorn1, Y. Le Maho1, G. Duhamel2 1Centre d¹Ecologie et Physiologie Energétiques, 23 rue Becquerel, 67087 Strasbourg Cedex 2, France 2Muséum National d¹Histoire Naturelle, Laboratoire d¹Ichtyologie Générale et Appliquée, 43 rue Cuvier, 75231 Paris Cedex 05, France *E-mail: charles.bost@c-strasbourg.fr ABSTRACT: The diving behavior and diet composition of King penguins were examined during summer 1995 at Kerguelen Islands. This was in relation to real-time estimations of diel prey availability during 2 sampling sessions totaling 10 d at sea. During daylight hours King penguins performed medium to deep dives of 120-250 m. At night, they dived no deeper than 60 m. Daytime, dusk and night-time sampling of prey was performed in the depth ranges corresponding to the depths of the penguins¹ dives in this study. The diversity in mesopelagic fish was found to be highest during the night at 0-50 m (15 vs 9 species during the day), and their number was up to 20-fold higher at these depths at night than during the day at the 150-250 m depth layer. The 3 myctophid species Electrona antarctica, Gymnoscopelus fraseri and G. braueri which were present in large sub-surface numbers during the night were virtually absent from the penguins¹ diet. The 2 species dominant in their diet, Muraenolepis marmoratus and Krefftichtys anderssoni (56.5 and 32.9% by number, 30.3 and 31.6% by biomass, respectively), were scarcely detected in the penguins¹ diving range during the night. In contrast, these 2 species, of which only the latter is bioluminescent, were significantly present during the day in the 0-300 m depth range (16.5 and 30.0% of the diurnal catches by number, respectively). In terms of biomass, these 2 prey types constituted only 6.3 and 12.6% of the total daylight trawls, which were dominated by the genus Protomyctophym (38.6% of the catches). The overlap between the penguins¹ diet and trawl content was the most significant with daylight sampled data. King penguin feeding success seems mostly dependent on deep dives during the day, despite lower prey availability than during the night. Ambient light levels, which were found to be higher at deeper depths (150-180 m) during the day compared to the sub-surface (0-60 m) at night-time, therefore appear to better determine King penguin foraging success than diel migration of prey to shallow depths. KEY WORDS: King penguins · Diet · Diel vertical migration · Myctophids · Foraging behavior Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 227. Online publication date: February 13, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

ADULT SIZE OF EIGHT HUNTING SPIDER SPECIES IN CENTRAL AMAZONIA: TEMPORAL VARIATIONS AND SEXUAL DIMORPHISMS

Abstract We studied temporal variation in adult size and sexual size dimorphism (SSD) of seven hunting spider species, Ctenus amphora, C. crulsi, C. manauara, C. villasboasi (Ctenidae), Phoneutria fera, P. reidyi (Ctenidae), and Ancylometes rufus (Pisauridae) in a tropical rainforest, and one species from a relatively open vegetation habitat, C. minor, in central Amazonia. Size variation was great within and among field trips. Spiders were generally smaller in October (end of dry season) when compared with other months: adults of C. amphora, C. crulsi and C. manauara were significantly smaller in October 1995 when compared to February 1996; P. fera were smaller in October 1998 than in June 1998; and A. rufus were smaller in October 1998 than in August 1998. The temporal variation in size is possibly a result of low prey availability during the dry season. Six species had significant differences in prosoma length between males and females: C. amphora, C. crulsi, C. manauara and C. minor had larger males (w...

Seasonal Variation in Reproductive Traits of the Oviparous Water Snake, Natrix maura, in the Ebro Delta of Northeastern Spain

Seasonal Variation in Reproductive Traits of the Oviparous Water Snake, Natrix maura, in the Ebro Delta of Northeastern Spain

Predation by inland silversides on an exotic cladoceran, Daphnia lumholtzi, in Lake Texoma, U.S.A.

In the early 1990s, Lake Texoma was invaded by Daphnia lumholtzi, a large, spiny, exoticcladoceran. From April 1994 to April 1995 D. lumholtzi was most abundant in the lake in mid‐summer, after native zooplankton declined in early June. Inland silversides Menidia beryllina selectively preyed on D. lumholtzi but appeared to prefer the large native zooplankton when they were present. Daphnia lumholtzi was an important prey item for silversides during summer when large native zooplankton was scarce. The invasion of D. lumholtzi into Lake Texoma may benefit some zooplanktivorous fishes by increasing foraging opportunities during a time of low prey availability.

Superfluous killing in spiders: a consequence of adaptation to food-limited environments?

The hypothesis that superfluous killing, partial consumption, and abandonment of prey is a consequence of adaptation to foodlimited environments was tested in two feeding trials on a desert spider, Agelenopsis aperta. First, we made comparisons among populations inhabiting sites of high prey (HP) or low prey (LP) availability that differed in their degree of genetic isolation. Typically, A. aperta entirely consumed one or two of the prey items it captured in a feeding bout. Additional prey were partially consumed or abandoned without eating. Spiders from the genetically isolated HP population, however, captured fewer prey and showed a higher incidence of full feeding on prey than did individuals from the other populations. Only one spider from this population captured a prey item that it failed to feed on, whereas spiders from LP populations failed to feed on high numbers of captured prey. The greatest variability in feeding behavior was exhibited in the HP population that experienced gene flow. The second test was based on the finding that aggressiveness is largely a sex-linked trait in A. aperta: the aggressiveness of the female parent only is inherited by male offspring, whereas both parents contribute to this trait in female offspring. All female F1 hybrids between LP and HP parental types exhibited high levels of superfluous killing, as did male F1 hybrids derived from LP females. F1 hybrid males derived from HP females exhibited extremely low levels of superfluous killing. Superfluous killing thus has its basis in the genetic control of levels of aggression.

Competitive Interactions between Coyotes and San Joaquin Kit Foxes

Competitive interactions between coyotes ( Canis latrans ) and federally endangered San Joaquin kit foxes ( Vulpes macrotis mutica ) were investigated at the Naval Petroleum Reserves in California (NPRC) during 1984–1995. Coyotes and kit foxes used similar food items, indicating the potential for exploitative competition. Leporids were the primary prey for coyotes in all years, but small rodents were the primary prey for kit foxes in most years, although leporids were primary prey in other years. Coyotes were the main cause of mortality to kit foxes at NPRC, indicating that interference competition may be occurring. Population trends of kit foxes appeared to be strongly influenced by food availability, but competition from coyotes also may have affected population dynamics of kit foxes. Mechanisms employed by kit foxes, such as resource partitioning, greater dietary breadth, and year-round den use, may facilitate coexistence with coyotes. However, use of anthropogenic food sources by coyotes may intensify competitive interactions during periods of low prey availability.

Nutritional condition and vertical distribution of Baltic cod larvae

Newly hatched Baltic cod Gadus morhua larvae are typically found at depths >60 m. This is a region of low light and prey availability, hence generating the hypothesis that larvae have to migrate from hatching depth to the surface layer to avoid starvation and improve their nutritional condition. To test this hypothesis, Baltic cod larvae were sampled during the spawning seasons of 1994 and 1995 with depth‐resolving multiple opening/closing nets. Each larva was aged by otolith readings and its RNA/DNA ratio was determined as a measure of nutritional condition. The RNA/DNA ratios of these larvae aged 2‐25 days (median 10 days) ranged from 0.4 to 6.2, corresponding to levels exhibited by starving and fast‐growing larvae in laboratory calibration studies (starvation, protein growth rate, Gpi= ‐12.2% day−1; fastgrowing larvae, Gpi=14.1%day−1) respectively. Seventy per cent of the field caught larvae had RNA/DNA ratios between the mean values found for starving and fed laboratory larvae. Only larvae aged 8‐11 days had higher mean RNA/DNA ratios above 45 m than below (t‐test, P<0.05). However, the instantaneous protein growth rates were significantly higher for all larval age groups in the surface layers (t‐test, P<0.05). Starving larvae were found in all depths sampled (10‐85 m), whereas growing larvae (positive Gpi) were restricted to samples taken shallower than 45 m. These superior growth rates above 45 m corroborate the hypothesis and imply that migration to the shallow water layers is a prerequisite for good nutritional condition, growth and survival of Baltic cod larvae. The frequent occurrence of cod larvae older than 8 days in the deep water in poor condition suggests that a proportion of the larvae will die from Starvation in the deep layers of the Baltic Sea.

Diet and foraging behaviour of group‐living meerkats, Suricata suricatta, in the southern Kalahari

Slender‐tailed meerkats (Suricata suricatta) are small, diurnal, and gregarious mongooses which inhabit the semi‐arid regions of southern Africa. In the south‐western Kalahari, substantial fluctuations in productivity are caused by extreme seasonality in rainfall and temperatures. We observed the foraging behaviour of habituated meerkats from January to July, a period covering the entire birth season and stages of high and low prey availability. Insects were the most frequently occurring prey class (78.1%), of which larvae (33.4% total frequency) and adult Coleoptera (27.5% total frequency) were the most important prey items throughout the year. Reptiles were heavily utilized in terms of prey bulk‐an index of volume‐(19.9%), but not by frequency (9.2%). Consumption of Coleoptera was positively correlated with rainfall, and negatively with temperature. Meerkats used a mean of 6.7 ± 1.1 prey categories daily, and there were significant monthly differences in prey diversity in the diet. Dietary shifts were apparently related to fluctuations in prey availability and the presence of preferred prey. There were no differences between the sexes in dietary diversity or niche breadth, but pregnant and lactating females foraged at significantly higher rates than males. The timing of foraging activity altered over the months in response to changes in daylength and thermoregulatory constraints. Foraging behaviour and seasonality in foraging effort are described, and the implications of an insect prey base for meerkat socioecology are discussed.

Reproduction in the Rattlesnake, Sistrurus miliarius barbouri, in Central Florida

Reproduction in the Rattlesnake, Sistrurus miliarius barbouri, in Central Florida

Influence of reduced food availability on growth of captive American kestrels

Captive American kestrels (Falco sparverius) were used to model the effect of low prey availability on growth and survivorship potential in nestling raptors. The experimental design consisted of 4 treatments: nestlings were fed ad libitum (100% diet) or on increasingly restricted diets (90, 80, and 70% of the ad libitum diet). Nestlings fed a reduced diet grew significantly more slowly than those fed the ad libitum diet, as shown by the body mass growth constant. The restricted diet had no significant effect on the asymptotic size of the kestrels, i.e., body mass and tarsus and antebrachium lengths. However, young kestrels fed reduced diets (80 and 70%) had a lower body mass at fledging than those fed ad libitum and the 90% diet, although they fledged at the same age. The growth of the ninth primary was slower for birds on restricted diets than for those fed ad libitum. Sexual dimorphism was observed for body mass and antebrachium growth constants, with males growing faster than females. However, females reached a higher asymptotic body mass and antebrachium length, as well as a higher body mass at fledging, than males. Thus, when prey availability is reduced by as much as 30%, nestling kestrels grow more slowly and store less fat, which could lead to poorer postfledging survivability.

Insular Radiation in Life History of the Lizard Eumeces okadae in the Izu Islands, Japan

The life history of Eumeces okadae, an endemic lizard of the Izu Islands, Japan, was studied to determine whether life-history traits varied in relation to island biota. Analysis of predation revealed that populations of E. okadae were classifiable into three types that suffered predation mainly from insectivorous birds, snakes, or carnivorous mammals. Extremely high population densities (>100 lizards seen per hour of census) were found on islands where only avian predators were present. A suite of traits, including annual reproduction, large clutches (8.8) of small eggs (412 mg), and early maturity (2 yr) with a small body size at maturity (64 mm SVL), was found on islands with a high predation intensity mainly from carnivorous mammals. Biennial reproduction, small clutches (6.57.5) of large eggs (569-591 mg), and delayed maturity (3-4 yr) with a large mature size (72-75 mm) were found on islands with low overall predation but potentially severe predation on juveniles from insectivorous birds. Intermediate life-history traits were found on islands with moderate predation pressure from snakes. Analyses of prey abundance and stomach contents suggested that E. okadae on high-density islands experienced low prey availability, probably because of exploitation and intraspecific competition. Strong predation impact, along with variation in prey availability and intensity of intraspecific competition, have molded the ecological course of divergence in the life history of different E. okadae populations.

Effect of cassava exudate and prey densities on the survival and reproduction of Typhlodromalus limonicus (Garman & McGregor) s.l. (Acari: Phytoseiidae), a predator of the cassava green mite, Mononychellus tanajoa (Bondar) (Acari: Tetranychidae)

The effects of cassava exudate and prey densities on reproduction and survival of the predatory mite, Typhlodromalus limonicus (Garman & McGregor) (Acari: Phytoseiidae), were investigated in the laboratory. Females were provided either cassava exudate ad lib. daily, low or high numbers of the cassava green mite prey, Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) daily, or exudate for 5 or 10 days before switching to a low or high prey diet. Females fed only exudate laid no eggs. Females fed exudate before prey experienced a significant decrease (30%) in the number of eggs laid compared to females fed high numbers of prey daily. The reduction in fecundity was the result of prolonged preoviposition periods (2.0 days on prey daily vs 4.0 days on exudate before prey) and reduced number of eggs laid per female per day (1.7 eggs per female per day on prey daily vs 0.4 eggs per female per day on exudate before prey). Females fed only exudate had a greater survival rate and longevity than females fed prey daily or females fed exudate before a diet of prey. These results suggest that T. limonicus can survice for a limited period on cassava exudate during periods of low prey availability, but requires prey to complete oogenesis and propagate the population.

The reproductive success of the dipper Cinclus cinclus in relation to the acidity of streams in south‐west Scotland

SUMMARY1. The breeding success of dippers Cinclus cinclus was assessed in south‐west Scotland over 3 years and related to the acidity of the streams along which they bred.2. At sites of high acidity, clutch and brood sizes were significantly smaller than those at sites of lower acidity.3. Egg weight and the incidence of second clutches increased significantly with pH, but there was no evidence to suggest an effect of acidity on hatching success.4. The rate at which food was delivered to individual nestlings was significantly lower at acidic than non‐acidic sites. Nestling weights and survival were lower at more acidic sites.5. Reduced brood sizes, low nestling survival and the low incidence of second brooding attempts resulted in a significant reduction in total productivity (number of fledglings produced, per pair, per year) at acidic compared with non‐acidic streams.6. It is suggested that pH‐related differences in the invertebrate fauna of streams result in low prey availability for dippers on acidic streams, leading to reduced productivity.

Dartford Warblers Follow Stonechats While Foraging

Some insectivorous birds wintering in an open Mediterranean habitat show following behaviour. Only typical gleaner species, such as the Dartford Warbler Sylvia undata, behaved as followers, whereas sit-and-wait species, such as the Stonechat Saxicola torquata, were followed. Both single individuals and homoor heterospecific flocks acted as followers. The composition of the following flock was highly dynamic, both with respect to number of species and individuals. The result was ephemeral groups consisting of one host and one or more follower individuals which usually broke up when the followed bird flew to a perch without being followed. We analysed the follower-followed relationships between the most interactive pair of species (Dartford Warbler and Stonechat). Following behaviour appeared to consist of two behavioural components: to follow the host when it changed foraging site and to glean prey close to it. When together with a Stonechat, the Dartford Warbler looked for prey mainly on the ground close to the former; when searching alone, it fed mainly in shrubs. The host may be a reliable and predictable indicator of optimum search areas, or the warbler may exploit its vigilance when looking for prey on the ground, or both. The proximity of a follower species altered the searching behaviour of the Stonechat and reduced its capture success by half. The Stonechat's antiparasite strategy mainly consisted of perch changes, to avoid interference. The ecological conditions favouring the development of this kind of following behaviour (habitat openness, cold temperatures, low prey availability, etc.) are discussed.

Predation on moose and caribou by radio-collared grizzly bears in east central Alaska

Radio-collared grizzly bears (Ursus arctos) were sighted daily for approximately 1-month periods during spring, summer, and fall to estimate predation rates. Predation rates on adult moose (Alces alces) were highest in spring, lowest in summer, and intermediate in fall. The highest kill rates were by male grizzlies killing cow moose during the calving period. We estimated that each adult male grizzly killed 3.3–3.9 adult moose annually, each female without cub(s) killed 0.6–0.8 adult moose and 0.9–1.0 adult caribou (Rangifer tarandus) annually, and each adult bear killed at least 5.4 moose calves annually. Grizzly predation rates on calves and grizzly density were independent of moose density and are probably more related to area-specific factors, e.g., availability of alternative foods. An important implication of our results is that managers should not allow moose densities to decline to low levels, because grizzlies can have a greater relative impact on low- than on high-density moose populations and because grizzly predation can be difficult to reduce. Grizzly bears were primarily predators, rather than scavengers, in this area of low prey availability (11 moose/grizzly bear); bears killed four times more animal biomass than they scavenged.

Behaviour of young Ringed Plovers Charadrius hiaticula and its relationship to growth and survival to reproductive age

The behaviour, growth and survival of Ringed Plover chicks were studied in 1974 at Mestersvig, northeast Greenland, and from 1973 to 1976 at Lindisfarne, northeast England. Post‐fledging survival, dispersal and recruitment were also investigated for the Lindisfarne population.Growth rates were similar in both study areas, and to those reported from other sites. A diurnal rhythm in feeding activity was more evident in the Arctic than at temperate latitudes, despite continuous daylight in the former area. This was correlated with low nocturnal temperatures and prey availability. It is concluded that food supply did not limit growth or chick survival in either study area. Brooding decreased progressively during the pre‐fledging period; the relationship of brooding period to age, environmental conditions and area was investigated. The adaptations of feeding and brooding behaviour for arctic and temperate breeding Ringed Plovers are discussed.Survival from hatching to fledging varied between 40% and 60% in different areas and years, and at least 59% of birds survived from fledging to about one year old. Minimum survival from one to two years old was only 57%. but year‐to‐year survival of older birds was higher, that of breeding adults being at least so?;. Most birds returned to the breeding area and attempted to breed when one year old. The extent of dispersal from Lindisfarne and the wintering areas of the Lindisfarne‐breeding birds are investigated.

Feeding chronology, daily ration, and the effects of temperature upon gastric evacuation in the pipefish,Syngnathus fuscus

Feeding chronology, daily ration, and the effects of temperature upon gastric evacuation were examined in the pipefish,Syngnathus fuscus, from field and laboratory data.S. fuscus displayed a pattern of diurnal feeding, characteristic of syngnathids. Daily ration calculations yielded estimates of 4.0 and 4.4% body weight per day, which are comparable to estimates for other teleosts. Evacuation rate was found to be temperature dependent. with more rapid evacuation with increasing temperature. In addition, evacuation rate was found to be positively correlated with gut content. Slowing of evacuation rate with decreasing gut content may allow for increased assimilation efficiency during periods of low food availability. Daily ration, although controlled by the temperature dependence of evacuation rate, may also be controlled by prey abundance; fish maximize food intake during periods of high prey availability, and maximize upon assimilation during periods of low prey availability.

Effect of food level on reproduction and metamorphosis in the suctorian protozoanTokophrya lemnarum stein

A sessile predator, the ciliated protozoanTokophrya lemnarum, produces a motile embryo. The embryo attaches to a substrate and secretes a stalk at metamorphosis. Production of the offspring is closely synchronized with the feeding schedule, so that fecundity per individual varies directly with the food level. Some embryos produced by an adult do not attach at metamorphosis but become freely floating adults. The percentage of nonattaching embryos is compared between adults fed high or low level diets. Adults on the low level diet produce 25% or more nonattaching embryos compared to 10% or less produced by adults on a high level diet. If the adult is switched from a low level diet to a high level diet, or from high to low, the percentage of nonattaching embryos produced on each diet remains relatively constant. It is suggested that nonattachment provides one means for individuals to escape areas of low prey density and availability.

On the Foraging Strategies of Carnivorous Plants: I. Evidence for an Adaptive Response to Low Prey Availability in the Venus' Fly Trap, Dionaea muscipula

On the Foraging Strategies of Carnivorous Plants: I. Evidence for an Adaptive Response to Low Prey Availability in the Venus' Fly Trap, Dionaea muscipula