Research Article
Ecological traits of declining amphibians in upland areas of eastern Australia
- Jean-Marc Hero, Stephen E. Williams, William E. Magnusson
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- Published online by Cambridge University Press:
- 18 October 2005, pp. 221-232
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Catastrophic declines of amphibian populations have been reported from upland areas around the world, yet within regions not all species have been affected. Herein, we examine the relationships between conservation status and ecological traits for over 60 amphibian species from upland areas of eastern Australia. Among the 24 phylogenetic groups examined, eight groups contained only declining species, eight groups contained both declining and non-declining species and eight groups had no declining species, suggesting species declines are influenced by their evolutionary history. Declines have been reported for only one species (Philoria frosti) of 20 species (i.e. from genera Assa, Cophixalus, Austrochaperina and remaining Philoria/Kyaranus) with direct development in the terrestrial environment. Of the remaining 40 species that include an aquatic stage in the life history, species-specific traits associated with declines suggest species with stream-dwelling tadpoles are more likely to be declining than species that breed in ephemeral and isolated ponds. However, low ovarian clutch size is the most important ecological trait significantly associated with the tendency for a species to be declining (independent of phylogeny). Species with restricted geographic ranges are also more likely to be declining than widespread species (independent of phylogeny). While ovarian clutch size and geographic range are correlated they are both good predictors for the likelihood of decline for upland species independent of their phylogenetic history. We propose that low ovarian clutch size is an index of low fecundity, and indicates a reduction in population resilience, making those species more susceptible to population declines and extinction than highly fecund species. This provides the first ecological explanation for why some species are declining while other sympatric species are not. Geographic range provides an easily applied tool that can be used to predict the likelihood of species decline in other regions. These results support the hypothesis that a causal factor may be affecting all species of frogs, yet only those species with naturally low population resilience are susceptible to declines.
Assessing the age of Reeves' muntjac (Muntiacus reevesi) by scoring wear of the mandibular molars
- Norma G. Chapman, W. A. B. Brown, P. Rothery
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- Published online by Cambridge University Press:
- 18 October 2005, pp. 233-247
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The skulls and mandibles of 50 (28 male, 22 female) captive muntjac Muntiacus reevesi of exactly known age and four (two male, two female) of approximately known age were examined for their molar wear patterns. A procedure for scoring was based on earlier published work (Brown & Chapman, 1990, 1991) for fallow Dama dama and red deer Cervus elaphus, respectively. Specimens were also available from 17 male and 13 female wild muntjac whose approximate ages were known. The data show a curvilinear relationship between age and toothwear score, with increasing variability as the score increases. The predicted age and upper and lower limits of 95% prediction intervals are given for captive and wild muntjac deer. The range between upper and lower limits, though greater than was found for fallow and red deer, may still be a useful guide for assessing animals of unknown age.
Mandibular force profiles of extant carnivorans and implications for the feeding behaviour of extinct predators
- François Therrien
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- Published online by Cambridge University Press:
- 18 October 2005, pp. 249-270
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A biomechanical approach is used to model the mandibles of extant carnivoran predators (felids, canids, and hyaenids) as beams to gain insight into feeding behaviours. Because bite force applied at any given point along the mandible should be proportional to external dimensions at an analogous location (interdental gaps) on the mandible, patterns of variation in these dimensions will reflect the adaptation of the jaw to specific loads. The mandibular force profiles of extant carnivorans closely reflect particular feeding behaviours. Solitary hunters relying on a powerful canine bite to subdue their prey have a strong mandibular symphysis, while pack hunters delivering shallow bites have a relatively weaker one. Symphyseal shape also gives insight into the feeding behaviour of a predator: (1) a deeper-than-long symphysis indicates that stresses induced by the canine bite (or while cracking bones with the anterior dentition) are more important than those induced by struggling prey; (2) an equidimensional symphysis indicates that the symphyseal region is optimally designed to resist torsional stresses induced during prey capture and/or bone cracking; (3) a longer-than-deep symphysis indicates that stresses related to prey capture are predominant over those induced by the canine bite or while cracking bone. Mandibular force profiles of juvenile carnivorans also reflect documented ontogenetic changes in feeding behaviour. Because variation in mandibular cross-sectional properties are interpretable in terms of documented behaviours among extant predators, mandibular force profiles are developed to gain insight into the feeding behaviour of two extinct predators, Panthera atrox and Canis dirus. Results indicate that the feeding behaviour of P. atrox differed slightly from that of modern lions, as the powerful paws restrained prey more efficiently, while C. dirus hunted in a similar fashion to the gray wolf, although it may not have been an efficient bone cracker. Both extinct predators are inferred to have had a more powerful bite than their extant relatives.
Sexually dimorphic patterns of space use throughout ontogeny in the spotted hyena (Crocuta crocuta)
- Erin E. Boydston, Karen M. Kapheim, Russell C. Van Horn, Laura Smale, Kay E. Holekamp
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- Published online by Cambridge University Press:
- 18 October 2005, pp. 271-281
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Observational and telemetry data were used in a geographic information system database to document the ontogenetic development of sexually dimorphic patterns of space use among free-living spotted hyenas Crocuta crocuta in Kenya. No measures of space use were sexually dimorphic among den-dwelling cubs, nor were sex differences apparent among hyenas that had ceased using dens for shelter until these animals were c. 30 months of age. Significant sex differences emerged late in the third year of life, and persisted throughout the remainder of the life span; males were found farther from the geographic centre of the natal territory than were females, and the mean size of individual 95% utility distributions was larger for males than females. Most dispersal events by radio-collared males were preceded by a series of exploratory excursions outside the natal territory. All collared males dispersed, but no collared females did so. Most dispersing males moved only one or two home ranges away at dispersal, roughly 8–10 km distant from the natal territory, before settling in a new social group.
Diet and food resource use by the pygmy skunk (Spilogale pygmaea) in the tropical dry forest of Chamela, Mexico
- Lisette Cantú-Salazar, Mircea G. Hidalgo-Mihart, Carlos A. López-González, Alberto González-Romero
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- Published online by Cambridge University Press:
- 18 October 2005, pp. 283-289
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The diet and pattern of food resource use by the pygmy skunk Spilogale pygmaea, an endemic and threatened species of western Mexico, was evaluated in the tropical dry forest of Chamela, Jalisco. Analysis of scats (n = 104) and stomach contents (n = 5) obtained during 1997, 1998 and 2000 showed that pygmy skunks fed mainly on invertebrates. Insect larvae constituted the most represented food item in samples. During 2000, food resource use was quantified by comparing occurrence of available prey with occurrence of items found in scats. Even though pygmy skunks seem to be opportunistic foragers, some invertebrates were positively selected, such as insect larvae and Myriapoda, thus suggesting that pygmy skunks may target prey of high nutritional value. The diet varied considerably between consecutive dry and rainy seasons of the studied years, with little overlap in food items. Pygmy skunks may adjust food resource use in response to temporal variations in prey abundance, by incorporating other food items in their diet during the dry season, when food is scarce. Dietary switching between seasons indicates that pygmy skunks may exhibit strategies similar to those of other tropical carnivores to deal with a highly seasonal environment.
Alternating sexual segregation during the mating season by male African buffalo (Syncerus caffer)
- Wendy C. Turner, Anna E. Jolles, Norman Owen-Smith
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- Published online by Cambridge University Press:
- 18 October 2005, pp. 291-299
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Patterns of association in many ungulate species vary throughout the year, with males periodically segregating from females. Sexual segregation can occur if males and females use different habitats (habitat segregation), occupy exclusive ranges (spatial segregation) or occur in separate social groups (social segregation). Previous studies on social segregation in ungulates have focused mostly on non-reproductive periods and species in temperate systems with short mating seasons. This study examined social segregation in African buffalo Syncerus caffer at Hluhluwe-iMfolozi Park, South Africa, during their 6-month mating season. During this period, mature male buffalo alternated between joining mixed-sex herds which comprise females and young, and small all-male groups. Activity patterns of male buffalo in both group types were examined to determine if differences in time allocation or activity asynchrony could explain the observed segregation. Mature males foraged for less time than both adult females and younger males when they were with mixed herds. Mature male buffalo differed in how their active time was apportioned to foraging and reproductive activities between the two group types. Females maintained group cohesion despite only low synchrony in activity, therefore segregation of male buffalo could not be explained by the activity budget hypothesis. For males in mixed-sex herds, reproductive activities were apparently at the expense of foraging time. The high time and energy costs of reproductive activities were probably responsible for the periodic separation of male buffalo from mixed herds during the extended mating period.
Ecological correlates of home-range size in spring–summer for female roe deer (Capreolus capreolus) in a deciduous woodland
- Sonia Saïd, Jean-Michel Gaillard, Patrick Duncan, Nadine Guillon, Noël Guillon, Sabrina Servanty, Maryline Pellerin, Karen Lefeuvre, Cécile Martin, Guy Van Laere
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- Published online by Cambridge University Press:
- 18 October 2005, pp. 301-308
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Data on 22 radio-collared adult female roe deer Capreolus capreolus in the Chizé forest were used to test whether their home-range size was influenced by resource availability and reproductive status. As roe deer females are income breeders and invest heavily in each reproductive attempt, they should be limited by energetic constraints. Thus it was expected that: (1) heavier females should have larger home ranges; (2) that home-range size should decrease with increasing vegetation biomass; (3) home-range size should increase with increasing reproductive effort (i.e. females with two fawns at heel should have larger home ranges than those with one fawn, which should have larger home range than females without fawns). To test these predictions, variation in spring–summer home-range size was studied in 2001 and 2002, using 95% kernel home-range estimation. Results showed that females do not adjust their home-range size in response to body mass or age. Home-range size increased with increasing reproductive success, but the magnitude of the change varied over the period of maternal care. Finally, although their home-range size decreased with increasing plant biomass (slope = −0.11, SE=0.065), female roe deer at Chizé did not fully compensate for declines in food availability by increasing home-range size.
Prey preferences of the lion (Panthera leo)
- Matt W. Hayward, Graham I. H. Kerley
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- Published online by Cambridge University Press:
- 18 October 2005, pp. 309-322
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Lions Panthera leo are generally thought to prey on medium to large ungulates. Knowledge of which species are actually preferred and which are avoided is lacking, however, as is an understanding of why such preference or avoidance may arise. An analysis of 32 studies over 48 different spatial locations or temporal periods throughout the distribution of the lion shows that it preferentially preys upon species within a weight range of 190–550 kg. The most preferred weight of lion prey is 350 kg. The mean mass of significantly preferred prey species is 290 kg and of all preferred species is 201 kg. Gemsbok, buffalo, wildebeest, giraffe and zebra are significantly preferred. Species outside the preferred weight range are generally avoided. Species within the preferred weight range that are not significantly preferred (such as roan, sable and eland) generally have features that reduce predation either morphologically (e.g. sable horns), ecologically (e.g. roan and sable occurring at low density), or behaviourally (e.g. the large herd size and increased vigilance of eland). Warthog are below the preferred weight range yet are taken in accordance with their availability and this is probably due to their sympatry with lion, their relatively slow evasion speed and their lower level of vigilance. Plots of prey preference against prey body mass follows a bell curve with a right skew that, we argue, is caused by collective hunting by lions of larger-bodied prey. Our methods can be used on all large predators and are likely to be useful in assessing competition in sympatric communities of predators, cooperative hunting and predicting predator diets. This will allow us to move beyond descriptive dietary studies to improve our predictive understanding of the mechanisms underlying predator–prey interactions.
Comparative seasonal acclimatization of food and energy consumption in adjacent populations of common spiny mice (Acomys cahirinus)
- Michael Scantlebury, Uri Shanas, Daniel Afik, Abraham Haim
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- Published online by Cambridge University Press:
- 18 October 2005, pp. 323-328
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Animals inhabiting environments with low productivity and food availability commonly have reduced energy demands and increased digestive efficiencies. The dry matter intake (DMI), apparent digestible dry matter (ADDM), digestible efficiency (DE) and digestible energy intake (DEI) of two populations of common spiny mouse Acomys cahirinus were compared during both winter and summer under conditions of simulated water stress. Mice were captured from the north- and south-facing slopes (NFS and SFS) of the same canyon that represent mesic and xeric habitats, respectively. Measured variables were also compared between F1 mice that had been born to either NFS or SFS mice, and raised in the laboratory. SFS mice were able to assimilate energy more efficiently than NFS mice during the summer. By comparison, NFS mice were able to assimilate more energy during the winter. During winter, NFS mice assimilated more energy at low levels of water stress, whereas SFS mice assimilated more energy at higher levels. Differences were also apparent in F1 mice. It is therefore suggested that local climatic conditions can impose physiological adaptations that are retained in succeeding generations, creating unique meta-populations.