Low survival rate and high predation in the African hingeback tortoise Kinixys spekii

Live and dead Kinixys spekii were collected in the Sengwa Wildlife Research Area, Zimbabwe over a 12‐year period. Live tortoises were sexable at a midline plastron length of 100 mm; females were considered sexually mature at 140 mm (reached by age 9 years) and males at 120 mm (at age 7 years). Adult females were significantly larger than males, on average by 14 mm in length and by 1.43 times in mass. Mark–recapture analysis in a 2 km² area showed a population density of sexable tortoises of 0.16 ha^?1. The survival rate was estimated by recaptures, by the frequency distribution of age at death, and by the mean age of live tortoises, and averaged 0.74 year^?1. Seventy‐seven to 89% of dead tortoises showed evidence of predation, depending on the criteria used. Damage occurred in characteristic forms, loss of the front or rear of the plastron, or holes in the carapace and plastron, which were attributed to predation by mammals and ground hornbills, respectively. K. spekii had similar body size and sexual size dimorphism to Mediterranean tortoises (Testudo), but population density was much lower and the mortality rate was twice as high, probably due to the abundant African predators. High mortality was offset by a rate of juvenile growth twice that of Testudo.     

Ecosystem-level evidence for top-down and bottom-up control of production in a grassland stream system

Ecosystem-wide effects of introduced brown trout (Salmo trutta L.) and native river galaxias (Galaxiaseldoni McDowall) were studied by analysing ecosystem production budgets for two adjacent tributaries of a grassland stream-system in the South Island of New Zealand. One tributary was inhabited by brown trout, the other by river galaxias. No other fish species were present in either stream. The budget for the river galaxias stream indicated little top-down control of invertebrates by fish predation (river galaxias consumed ∼18% of available prey production). A large proportion of annual net primary production was required to support production by invertebrates (invertebrates consumed an average of ∼75% of available primary production), and mean surplus primary production (i.e. not consumed) was not significantly different from zero. Primary and secondary production were presumably mutually limiting in this system (i.e. controlled by simultaneous top-down and bottom-up mechanisms). In contrast, the budget for the brown trout stream indicated extreme top-down control of invertebrate populations by fish predation; essentially all invertebrate production (∼100%) was required to support trout production. Invertebrate production required only a minor portion of annual net primary production (∼21%) and primary production was presumably controlled by mechanisms other than grazing (e.g. sloughing, nutrient limitation). Predatory invertebrates had little quantitative effect on prey populations in either stream. Recent experimental studies of invertebrate behaviour, fish behaviour, and food-web structure in New Zealand streams with physically stable channels indicate that a trophic cascade should be observed in streams inhabited by brown trout, in contrast to those inhabited by native fish. The results reported here provide ecosystem-level evidence supporting this prediction. Received: 10 March 1997 / Accepted: 12 December 1997     

Brown trout and food web interactions in a Minnesota stream

1. We examined indirect, community‐level interactions in a stream that contained non‐native brown trout (Salmo trutta Linnaeus), native brook trout (Salvelinus fontinalis Mitchill) and native slimy sculpin (Cottus cognatus Richardson). Our objectives were to examine benthic invertebrate composition and prey selection of fishes (measured by total invertebrate dry mass, dry mass of individual invertebrate taxa and relative proportion of invertebrate taxa in the benthos and diet) among treatments (no fish, juvenile brook trout alone, juvenile brown trout alone, sculpin with brook trout and sculpin with brown trout). 2. We assigned treatments to 1 m² enclosures/exclosures placed in riffles in Valley Creek, Minnesota, and conducted six experimental trials. We used three designs of fish densities (addition of trout to a constant number of sculpin with unequal numbers of trout and sculpin; addition of trout to a constant number of sculpin with equal numbers of trout and sculpin; and replacement of half the sculpin with an equal number of trout) to investigate the relative strength of interspecific versus intraspecific interactions. 3. Presence of fish (all three species, alone or in combined‐species treatments) was not associated with changes in total dry mass of benthic invertebrates or shifts in relative abundance of benthic invertebrate taxa, regardless of fish density design. 4. Brook trout and sculpin diets did not change when each species was alone compared with treatments of both species together. Likewise, we did not find evidence for shifts in brown trout or sculpin diets when each species was alone or together. 5. We suggest that native brook trout and non‐native brown trout fill similar niches in Valley Creek. We did not find evidence that either species had an effect on stream communities, potentially due to high invertebrate productivity in Valley Creek.     

The potential of Chrysoperla rufilabris and Doru taeniatum as agents for dispersal of Spodoptera frugiperda nucleopolyhedrovirus in maize

The behaviour of two abundant predators in Mesoamerican maize crops, Chrysoperla rufilabris larvae and Doru taeniatum adults, towards healthy and nucleopolyhedrovirus-infected Spodoptera frugiperda larvae was compared. C. rufilabris did not discriminate between healthy and virus-infected prey, although the mean search time was approximately two times longer towards virus-infected larvae. In contrast, D. taeniatum directed a greater proportion of their attacks towards virus-infected prey but there was no significant difference in the search time. Prey consumption time did not differ significantly for each type of prey by either predator, although prey consumption was much faster in D. taeniatum. Viable virus was detected in D. taeniatum faeces up to 3 d after feeding on infected S. frugiperda larvae, whereas virus was inactivated in the gut of C. rufilabris. Both predators were shown to have acidic guts. A field experiment demonstrated that D. taeniatum that had fed on infected prey could contaminate foliage resulting in the transmission of the disease at a low prevalence (4.7%) to S. frugiperda larvae in a field maize crop.     

Selection and capture of prey in the African ponerine antPlectroctena minor (Hymenoptera: Formicidae)

Prey selection by Plectroctena minor workers is two-fold. During cafeteria experiments, the workers always selected millipedes, their essential prey, while alternative prey acceptance varied according to the taxa and the situation. Millipedes were seized by the anterior part of their body, stung, and retrieved by single workers that transported them between their legs. They were rarely snapped at, and never abandoned. When P. minor workers were confronted with alternative prey they behaved like generalist species: prey acceptance was inversely correlated to prey size. This was not the case vis-à-vis millipedes that they selected and captured although larger than compared alternative prey. The semi-specialised diet of P. minor permits the colonies to be easily provisioned by a few foraging workers as millipedes are rarely hunted by other predatory arthropods, while alternative prey abound, resulting in low competition pressure in both cases. Different traits characteristic of an adaptation to hunting millipedes were noted and compared with the capture of alternative prey. We also noted the parsimony of the behavioural phases during their capture compared to the capture of alternative prey.     

The impact of predation by burbot (<Emphasis Type="Italic">Lota lota</Emphasis> L.) on the macroinvertebrate community in the littoral zone of a large lake

We studied the effects of predation by juvenile burbot (Lota lota) on the macroinvertebrate community in mesocosm experiments in the stony littoral zone of Lake Constance, a large prealpine lake in Central Europe. Although the growth data of the burbot suggest that the benthivorous fish exerts strong predation pressure on the invertebrate community, the predicted level of consumption is only poorly reflected by changes in biomass and abundance of most invertebrate prey taxa. High exchange rates of the prey between the mesocosms and the ambient littoral environment apparently masked the true predation effects of fish. Also, life-history events such as hatching or synchronised emergence of larvae led to temporal effects that obscured the impact of predation. However, for the dominant prey organism, the freshwater amphipod Gammarus roeseli, direct lethal effects appeared when its migration was limited. When exchange with the ambient littoral zone was possible, abundance and biomass of G. roeseli were unexpectedly high in the mesocosms stocked with burbot, indicating behavioural responses to fish presence. During the experiment, the burbot gained ca. 15% in length and about 60% in body mass. According to stomach content analyses at the end of the experiment, the ingested prey consisted mainly of relatively large and abundant invertebrates. Our study indicates that predation by juvenile burbot should be an important factor in structuring the benthic invertebrate community in terms of qualitative and quantitative effects.     

Observations on feed size and capture success in the larval butterfly splitfin (Ameca splendens Miller & Fitzsimons, 1971, Pisces: Goodeidae) reared on zooplankton

In this study, we quantified the feeding behaviour (encounter, attack, capture. and ingestion) of larval A. splendens on micro‐crustacean prey [cladocerans: Alona rectangula, Simocephalus vetulus (separately neonates and adults), Ceriodaphnia dubia, Daphnia pulex (juveniles), Moina macrocopa and ostracods: Heterocypris incongruens]. Although we initially (first 4 weeks) offered rotifers (Brachionus calyciflorus and B. patulus), they were not consumed by the larvae and hence observations with these prey were discontinued. Feeding behaviour was observed during the first 10 weeks. Fifteen observations were made with each prey species (seven diets × four replicates). Experiments were conducted in 50 ml transparent containers with 20 ml fish‐conditioned water into which one fry was introduced. Before introducing the fish, 20 individuals of a given cladoceran prey species or 50 individuals of a rotifer prey species were introduced. Until the fourth week, we used 20 ml of medium and thereafter 30 ml, but the prey density used remained constant (1 ind. ml⁻¹). Observations (10 min per fry per cladoceran replicate) were taken under a stereomicroscope (20×) for the first 2 weeks and later with a lamp and a magnifying lens. The number of encounters (E), attacks (A), captures (C) and ingestions (I) were recorded. During the study period, there was a 60% increase in gape size but only a 30% increase in body length. The number of encounters of larval A. splendens was highest (192) on M. macrocopa and lowest (29) on ostracods and adult S. vetulus (59). The inverse relationship between capture success and prey size was more pronounced during the latter half of the study period. Compared with all the other prey types offered, A. splendens fed maximally on M. macrocopa, which therefore could be a suitable diet for the larval rearing of this fish species.     

Comparative feeding ecology of Tropocyclops prasinus mexicanus (Copepoda, Cyclopoida)

The herbivorous and carnivorous feeding biology of Tropocyclopsprasinus mexicanus, an especially small cyclopoid copepod, wasstudied under in situ food conditions in three different lakesand under experimentally augmented food supplies. The mass-specificfood uptake is compared to that of two larger species—Cyclopskolensis and Cyclops vicinus. Under in situ food conditions,T.p.mexicanus depended to a larger extent on algae than invertebrateprey and showed lower mass-specific ingestion rates than thetwo larger species. Daily mass-specific uptake rates for algaeranged between 10 and 24% of its body mass versus 0.7–7%for invertebrate prey. The larger species C.vicinus and C.kolensisingested a total dry mass equivalent to 106% or up to 143% oftheir body mass with algae contributing 66 and 81%. However,under enriched food availability, T.p.mexicanus is able to ingesta biomass equivalent to its body mass, with an algae (54%) andprey (40%) portion similar to that of the larger species. Bodysize appears to be an important factor for the relative importanceof algal versus invertebrate prey for cyclopoid copepods.     

Foraging ecology of Gentoo Penguins Pygoscelis papua at Macquarie Island during the period of chick care

The diet, diving behaviour, swimming velocity and foraging range of Gentoo Penguins Pygoscelis papua were studied at Macquarie Island during the breeding season in the 1993–1994 austral summer. Gentoo Penguins are considered to be inshore feeders, and at Macquarie Island the diet and estimated foraging ranges supported this. The diet consisted of 91.6% fish and 8.3% squid, by mass. The dominant prey taxa were the fish Gymnoscopelus sp. and Paranotothenia magellanica. A mixture of pelagic and benthic prey was consumed, with a greater proportion of benthic species occurring later in the season. The penguins exhibited a strong diurnal pattern in their diving behaviour. Deep diving (≥30 m) began near sunrise (03.00 h) and finished close to sunset (21.00 h). Diving at night was less common and very shallow (<10 m). Early in the breeding season, dive profiles indicated that birds were probably following vertically migrating pelagic prey through the water column and were foraging in waters over 100 m deep. Later in the season, more uniform, shallower depths were used, suggesting an increase in benthic foraging activity. These changes in dive pattern and depth were consistent with the habitat preferences of prey species found in the diet. Gentoo Penguins swam at 1.04 m per s and had a maximum potential foraging range of about 26 km for single-day trips. They tended to forage within 14 km of the colony, with a mean range of 5.4 km. This range encompassed the deep ocean habitat to the west and east of the island and a shallow area to the north.     

SYSTEMATIC NOTES ON BIRDS OF THE CAPE PROVINCE: PART III.—PARISOMA SUBCAERULEUM (Vieillot): PART IV.—ANTHUS RICHARDI (Vieillot): PART V.—GALERIDA MAGNIROSTRIS Stephens

Fraser, M. W. 1984. Foods of Subantarctic Skuas on Inaccessible Island. Ostrich 55: 192–195.

Analysis of over 140 prey remains and 500 pellets of Subantarctic Skuas Catharacta antarctica collected from a site on Inaccessible Island. Tristan da Cunha, between October 1982 and January 1983 showed that 13 species of bird and one invertebrate were taken. Storm Petrels (Oceanitidae) made up 52% of the items recorded, Broadbilled Prions Pachyptila vittata 21%, and Common Diving Petrel Pelecanoides urinatrix 15%. Landbirds were rarely taken.     

Differential vulnerability determines the diet of a slow-moving predatory stream insect

1. We investigated the diet and prey electivity of Rhyacophila obliterata, a slow‐moving invertebrate predator capable of hunting in high‐flow microhabitats, and quantified the components of the predation sequence of fifth‐instar larvae foraging on mobile (Baetis mayflies, Amphinemura stoneflies) versus semi‐sessile (larval blackflies) prey. 2. In the field, fifth‐instar Rhyacophila consistently took more larval blackflies than more mobile prey. In behavioural trials, the number of attacks by Rhyacophila differed significantly between prey types, mobile prey being attacked more often than blackflies. Capture success, by contrast, was highest for blackflies, whereas Amphinemura and Baetis were rarely captured. In mixed‐prey feeding trials, Rhyacophila showed strong preference for blackflies and equally strong avoidance of Amphinemura and Baetis. 3. For mobile prey, the risk of being captured by this sluggish predator is very low, so they can afford to be in close contact with it. Rhyacophila was almost unable to capture any other prey but blackflies, resulting in strong passive selection for blackflies. 4. Therefore, the diet of fifth‐instar Rhyacophila can be predicted from laboratory observations and prey behaviour is the major determinant of the diet of this invertebrate predator.     

Age-specific Chaoborus predation on rotifer prey

SUMMARY. 1. This is the first study to examine predator-prey interactions between Chaoborm instars and rotifer prey. The predatory behaviour of instars I–III of Chaoborus pimctipennis and the diet selectivity of instars I—IV feeding on rotifers were examined in the laboratory. Prey used in direct observations of predatory behaviour included a variety of rotifers (Symhacta pectlnata, S. ohUmga, Polyarthra remata, Asplanchna girodi, Keratella crassa, spined and unspined forms of Keratella cochlearis) and two crustaceans (Bosmitia longirostris, Mesocyclops edax nauplii. 2. In general, strike efficiencies (percentage of strikes resulting in inges- tion) increased in successive instars I—III. Early instar (I and II) strike efficiencies were low when compared with other invertebrate predators. For a given instar. mean prey handling times varied among prey species more than strike efficiencies. Mean handling times for small, soft-bodied rotifers were lowest and those for wide, hard-bodied prey were highest. 3. Instar I exhibited significantly greater selectivity for the small, soft- bodied S. obUmga than for the larger S. pectinata, hard-bodied K. crassa, and spined and unspined forms of K. cochlearis. Instars II—IV positively selected both the large and small Symhaeta species over all Keratella species. The relationship between Chaobortts selectivity and prey value (weight of prey per unit handling time) can be described by a power function. Ingestion rates of rotifers by older instars (III and IV) are among the highest reported for invertebrate predators. 4. Rotifer vulnerability to Chaoborus predation probably depended on rotifer cuticle texture, body width, and hydrodynamic disturbances. Spined rotifers were not necessarily protected from Chaoborus predation because Chaohorus can manipulate and swallow them. Giguere et al.'s 1982) encounter rate model must be modified to predict encounter rates of slow-moving rotifer prey with Chaohorus.     

Invasive litter, not an invasive insectivore, determines invertebrate communities in Hawaiian forests

In Hawaii, invasive plants have the ability to alter litter-based food chains because they often have litter traits that differ from native species. Additionally, abundant invasive predators, especially those representing new trophic levels, can reduce prey. The relative importance of these two processes on the litter invertebrate community in Hawaii is important, because they could affect the large number of endemic and endangered invertebrates. We determined the relative importance of litter resources, represented by leaf litter of two trees, an invasive nitrogen-fixer, Falcataria moluccana, and a native tree, Metrosideros polymorpha, and predation of an invasive terrestrial frog, Eleutherodactylus coqui, on leaf litter invertebrate abundance and composition. Principle component analysis revealed that F. moluccana litter creates an invertebrate community that greatly differs from that found in M. polymorpha litter. We found that F. moluccana increased the abundance of non-native fragmenters (Amphipoda and Isopoda) by 400% and non-native predaceous ants (Hymenoptera: Formicidae) by 200%. E. coqui had less effect on the litter invertebrate community; it reduced microbivores by 40% in F. moluccana and non-native ants by 30% across litter types. E. coqui stomach contents were similar in abundance and composition in both litter treatments, despite dramatic differences in the invertebrate community. Additionally, our results suggest that invertebrate community differences between litter types did not cascade to influence E. coqui growth or survivorship. In conclusion, it appears that an invasive nitrogen-fixing tree species has a greater influence on litter invertebrate community abundance and composition than the invasive predator, E. coqui.     

Influence of season and body condition on plasma volume levels of white‐tailed deer,Odocoileus virginianus

Abstract

Changes in the circulating plasma volume were monitored for twelve consecutive months in five white‐tailed deer (Odocoileus virginianus) maintained outdoors in a 2.4‐ha enclosure in northern New York stale. The mean annual relative plasma volume of the two male white‐tailed deer (43.6 ± 1.0 ml/kg) was not significantly different from that of three females (45.7 ± 0.7 ml/kg). Mean annual absolute plasma volume, however, was significantly higher in males (2588 ± 90.7 ml) than in females (2092 ± 79.1 ml), mainly because of the greater body weights of males in late summer and early fall. Both sexes had a marked seasonality in the level of relative and absolute plasma volume regulation. Relative plasma volumes were lowest in February‐March and highest in May‐June and again in October, while absolute plasma volumes were lowest in late winter to early spring, when body weights in the annual cycle were lowest, and volumes were highest in mid‐fall, at the annual peak of body condition. Males had a greater excursion about their annual mean relative plasma volumes (‐16 to 13%) and absolute plasma volumes (‐23 to 32%) than did females (respectively, ‐11 to 9% and ‐13 to 19%). Variations in the level of plasma volume regulated are related to the annual cycle of environmental conditions and changes in body and physiological condition of white‐tailed deer.     

NOTICES

Steyn, P. 1975. Observations on the African Hawk-Eagle. Ostrich 46:87-105.

Observations extending over 12 years were made on two pairs of African Hawk-Eagles Hieraaetus spilogaster at Essexvale, Rhodesia. Details on various aspects of adult behaviour are given, particularly on hunting methods and calls. Nest repair usually took about 4–5 weeks. and limited observations indicated that the male does most of the work. Incubation is done mostly by the female, the male relieving her when he brings prey. The incubation period is 43 ± 1 day. Details are given of parental behaviour during the fedging period; time on the nest showed a progressive decline although both adults still perched in the. nest tree a great deal. The male provided most of the prey. The growth and behaviour of the eaglet Is described; usually the eaglet becomes a “brancher” before its first flight which, in four cases, occurred between 61–71 days. Post-of edping attachment to the nest lasted about three weeks in one case. Frief mention is made on the development of adult plumage. Birds made up 74%. mammals 25% and reptiles 1% of 104 prey items recorded at Essexvale. Gamebirds are preferred. The two nests had completely different breeding histories. One pair reared no young while the replacement rate of the other pair was 0,83 voung/pair/year. The combined replacement rate of the two pairs was 0,48 young/pair/year. There appear to be no records of two eaglets being reared together in southern Africa.     

Patterns of prey use by lesser scaup <Emphasis Type="Italic">Aythya affinis</Emphasis> (Aves) and diet overlap with fishes during spring migration

Recent decline in the lesser scaup Aythya affinis population has been linked to changes in wetland conditions along their spring migration routes. In particular, the use of amphipod prey by lesser scaup has declined in many regions of the upper Midwest U.S.A. and has been linked to expanded fisheries, although empirical data on diet overlap are lacking. To explore patterns of prey use by lesser scaup and diet overlap with fishes, we quantified diets of scaup and fishes during the 2003 and 2004 spring migration in eastern South Dakota, U.S.A. We compared diet overlap between lesser scaup and fishes collected from Twin Lakes, South Dakota—an important stopover location for spring-migrating scaup. Plant seeds occurred in >95% of lesser scaup diets (n = 118) and represented an appreciable amount of consumed biomass (>70%). Gastropods, amphipods, and chironomids were the most abundant invertebrate prey taxa and occurred in 29–34% of lesser scaup diets. Although relatively frequent, these taxa each contributed only 4–27% of the diet by weight. Percent dry mass of amphipods, a preferred prey by lesser scaup, was low (4%) indicating that amphipod availability may be reduced during spring migration. Analysis of fish diets showed that black bullhead Ameiurus melas and yellow perch Perca flavescens had the highest diet overlap with lesser scaup at 94% and 92%, respectively. Moreover, mean size of amphipods and chironomids found in fish diets were significantly larger than that consumed by lesser scaup. Our findings support the notion that amphipod use by spring-migrating lesser scaup has declined and that size-selective predation by fishes may influence prey availability for lesser scaup. Handling editor: K. Martens     

PRESENCE OF CIRCADIAN RHYTHMS IN THE LOCOMOTOR ACTIVITY OF A CAVE-DWELLING MILLIPEDE GLYPHIULUS CAVERNICOLUS SULU (CAMBALIDAE,SPIROSTREPTIDA)

The locomotor activity of the millipede Glyphiulus cavernicolus (Spirostreptida), which occupies the deeper recesses of a cave, was monitored in light-dark (LD) cycles (12h light and 12h darkness), constant darkness (DD), and constant light (LL) conditions. These millipedes live inside the cave and are apparently never exposed to any periodic factors of the environment such as light-dark, temperature, and humidity cycles. The activity of a considerable fraction of these millipedes was found to show circadian rhythm, which entrained to a 12:12 LD cycle with maximum activity during the dark phase of the LD cycle. Under constant darkness (DD), 56.5% of the millipedes (n = 23) showed circadian rhythms, with average free-running period of 25.7h ± 3.3h (mean ± SD, range 22.3h to 35.0h). The remaining 43.5% of the millipedes, however, did not show any clear-cut rhythm. Under DD conditions following an exposure to LD cycles, 66.7% (n = 9) showed faint circadian rhythm, with average free-running period of 24.0h ± 0.8h (mean ± SD, range 22.9h to 25.2h). Under constant light (LL) conditions, only 2 millipedes of 11 showed free-running rhythms, with average period length of 33.3h ± 1.3h. The results suggest that these cave-dwelling millipedes still possess the capacity to measure time and respond to light and dark situations. (Chronobiology International, 17(6), 757–765, 2000)     

Diet of brown-nosed coatis and crab-eating raccoons from a mosaic landscape with exotic plantations in southern Brazil

We described the diets of two procyonids, the brown-nosed coati Nasua nasua and the crab-eating raccoon Procyon cancrivorus, through analysis of stomach contents of road-killed specimens in southern Brazil. We compared them with previously published dietary information for another syntopic mesopredator, the crab-eating fox Cerdocyon thous. The landscape of the study area includes native grasslands, forests, exotic tree plantations, and other crops. Food items were represented by frequency of occurrence (FO) and relative volume (RV). Stomach contents of 23 coatis were analyzed. Animal and plant items were equally frequent, although the volume of plants was greater. Exotic plant species were consumed more than native plants. Among prey items, invertebrates were more important than vertebrates, mainly because of the frequency of coleopterans and annelids and the volume of necrophagous dipteran larvae. Five specimens of raccoons were analyzed, in which animal items had the highest FO and plant items had the highest RV. Both invertebrate and vertebrate prey had the same FO, although vertebrates had a higher RV. Our data suggest that these procyonids are opportunistic hypocarnivores, utilizing anthropic sources, with diet overlap. The coatis also overlapped their diet substantially with the foxes. The stomach-contents analysis revealed the importance of fruit pulp biomass, soft-bodied animals such as larvae, and also soil, which might indicate feeding habits such as scavenging and geophagy.     

Dietary partitioning of three large carnivores in Majete Wildlife Reserve,Malawi

Between 2011 and 2012, the carnivore guild in Majete Wildlife Reserve (MWR), Malawi, was restored following the reintroduction of lion (Panthera leo) and leopard (Panthera pardus). The aim of this study was to describe and compare the diet of lion, leopard and resident spotted hyaena (Crocuta crocuta) using scat analysis. Lions and spotted hyaenas displayed the greatest dietary overlap (O_ab = 0.88) and selected mainly medium- to large-bodied prey species. Lions had a mean preferred prey weight of 120.33 ± 42.14 kg (SE), with warthog (Phacochoerus africanus) and waterbuck (Kobus ellipsiprymnus) making up 60.64% of relative biomass consumed. Spotted hyaenas had a mean preferred prey weight of 102.40 ± 41.69 kg and had a more generalised diet (B_a = 0.46) compared to lions (B_a = 0.36). In contrast, leopards occupied a dietary niche substantially lower than that of lions and spotted hyaenas, selecting relatively smaller prey with a mean preferred prey weight of 27.50 ± 6.74 kg. Our results suggest that coexistence between the resident hyaena and reintroduced lion and leopard in MWR is facilitated by dietary partitioning. We advise long-term monitoring of reintroduced carnivores in small, enclosed reserves to assess their impacts on predator and prey populations.     

Interactions between adult and larval bluegill sunfish: positive and negative effects

Adult fish may affect the growth and survival of conspecific larvae through a variety of pathways, including negative interactions via competition for shared limiting resources or via predation (i.e., cannibalism), and positive interactions due to the consumption of larval predators and via resource enhancement (i.e., presence of adults increases availability of larval prey). To examine the overall effect of adult bluegill sunfish (Lepomis macrochirus) on larval bluegill, we conducted a field experiment in which we manipulated adult densities and quantified larval growth and survival, prey abundance, invertebrate predator abundance, and cannibalism. The presence of adult bluegill had a negative effect on final larval mass. This response was consistent with competition for zooplankton prey. Adult bluegill reduced the abundance of large zooplankton (e.g., Chaoborus and Daphnia), which were the dominant prey of bluegill larvae in the absence of adults. Larvae in the no-adult treatment also had significantly more prey in their stomachs compared to larvae in the presence of adults. Larval survival was maximized at intermediate adult densities and the overall production of larvae peaked at intermediate adult densities. The higher larval survival at intermediate adult densities is attributed to a reduction in invertebrate predators in treatments with adult bluegill; invertebrate predators experienced an 80% reduction in the presence of adult fish. Decreased larval survival at the highest adult density was not due to resource limitation and may be due to cannibalism, which was not directly observed in our study, but has been observed in other studies.