Continental patterns in the diet of a top predator: Australia's dingo

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Biodiversity friend or foe: land use by a top predator,the dingo in contested landscapes of the Australian Wet Tropics

Dingoes (Canis dingo) in the coastal lowlands of Australia's Wet Tropics are perceived as a major threat to biodiversity and subjected to broad‐spectrum lethal control. However, evidence of their impacts is equivocal, and control programmes generally ignore the ecological benefits that dingoes might provide. Previous diet analysis has shown that dingoes in the Wet Tropics primarily prey on common, terrestrial mammals. However, little is known of dingo habitat use or prey acquisition in the region despite these activities having major implications for biodiversity conservation. We investigated land use by dingoes in the lowland Wet Tropics to enable predictions of potential prey types, relative prey use and modes of prey acquisition. Nine dingoes were tracked for 3–6 months. Home ranges and resting areas were estimated using multiple estimators, and habitat use was analysed using compositional analysis of habitat use and generalized additive models. Dingo ranging behaviour suggested that anthropogenic food subsidies were infrequently used. Each territory comprised several sclerophyll forest rest areas with adjacent sugarcane‐grassland high activity areas. Individuals used each rest‐activity area for extended durations before moving on to another. Sclerophyll and rainforests, which contain the fauna species of primary conservation concern, were generally used for rest/sleep, or movement between rest‐activity areas. Activity patterns were consistent with dingoes hunting in open sugarcane‐grassland habitats during daylight hours. Dingo activity was low in areas where fauna species of conservation concern occur, which suggests that dingoes do not pose a threat to their survival. Consequently, current broad‐spectrum lethal control may have minimal benefits or even incur costs for biodiversity. Maximizing the ecosystem services provided by dingoes while simultaneously minimizing their negative impacts requires a more targeted location‐specific management approach, one that assesses and mitigates impacts specifically where background circumstances suggest particular packs may be either a conservation or economic threat.     

Group size versus territory size in group-living badgers: a large-sample field test of the Resource Dispersion Hypothesis

Badgers ( Meles meles ) have been the focus for the development of a pervasive model of social grouping behaviour, relevant to a number of carnivore species and other taxonomic groups – the Resource Dispersion Hypothesis (RDH). The RDH hypothesises that the dispersion and richness of resources in the environment provide a passive mechanism for the formation of groups, even without any direct benefits of group living. However, few studies have tested the RDH in the field. The principal prediction is that, as opposed to enlargement of territory sizes to accommodate more members, territory size (TS) is independent of group size (GS). Instead, TS is determined by the spatial dispersion of resources, while GS is independently determined by the richness of those resources. However, these predictions provide only weak correlative tests, especially in non-experimental field studies. The first predicts an absence of correlation and is therefore prone to Type II error, especially given the small sample sizes and errors in estimating TS and GS of mammals in the field. We tested for independence of territory size and group size in all years with available data since the beginning of the long-term badger study in Wytham Woods in 1974. We used two methods of TS estimation, a sequential Bonferroni technique to adjust for multiple inference tests, a combined analysis and an analysis with pooled data. This prediction of the RDH could not be rejected on the basis of any of these analyses. Given this evidence that other processes are independently determining group size and territory size, further predictions of the RDH will be worth investigating in considerable detail.     

Sentenced without trial: reviling and revamping the Resource Dispersion Hypothesis

The resource dispersion hypothesis (RDH) offers a predictive model for how, in heterogeneous environments, some animals may form groups even without any direct benefits from doing so. Revilla (2003) levels a number of criticisms at the RDH, all of which we feel can be easily clarified or resolved (we address them in the order they appear in his critique). We argue that the RDH, despite its long history and despite our own efforts, still lacks convincing evidence to reject it. On the contrary, we see it as having weathered its critics very well. While there is steadily accumulating evidence in support of the RDH, there are very few empirical tests that provide decent evidence against it.     

Climate-driven range expansion of a critically endangered top predator in northeast Atlantic waters

Global climate change is driving rapid distribution shifts in marine ecosystems; these are well established for lower trophic levels, but are harder to quantify for migratory top predators. By analysing a 25-year sightings-based dataset, we found evidence for rapid northwards range expansion of the critically endangered Balearic shearwater Puffinus mauretanicus in northeast Atlantic waters. A 0.6 degrees C sea surface temperature increase in the mid-1990s is interpreted as an underlying controlling factor, while simultaneous northward shifts of plankton and prey fish species suggests a strong bottom-up control. Our results have important conservation implications and provide new evidence for climate-driven regime shift in Atlantic ecosystems.     

Evaluating the influence of diet-related variables on breeding performance and home range behaviour of a top predator

Diet composition is linked to reproductive performance directly or indirectly by other life-history traits, including home range behaviour. The relationships between prey abundance, diet and individual fitness have often been explored. However, these relationships are complex and difficult to disentangle, especially in vertebrate top predators. Here, we present the results of a long-term study using multi-model inference procedures to elucidate the influence of diet-related variables on breeding parameters and home range behaviour of a top predator, the eagle owl Bubo bubo. Superpredation, diet diversity, rat biomass and rabbit mean weight were the most important variables when analysing reproductive parameters, suggesting that less diverse diets with greater rabbit biomass percentage may benefit reproductive performance, whereas rat biomass percentage is apparently associated with greater variation of breeding success. Earlier laying dates seem to be associated with the consumption, on average, of smaller rabbits. On the other hand, edge density was the most relevant factor determining the variation in home range behaviour, with individual characteristics, such as age and sex, also being important. Although the relative importance of the diet-related variables was generally low, mean weight of alternative prey, diet diversity and rabbit biomass also helped to explain home range parameters. In an optimal foraging context, centred on the abundance of the main prey species, our results suggest that when rabbits are less available eagle owls may increase home range size in order to obtain alternative prey, increasing at the same time their dietary diversity, which may also require higher movement speed.     

Home range, activity and movements of a wolf pack in central Italy

Home range, habitat use, activity and movement patterns were studied in a pack of wolves in a mountainous region of Abruzzo, central Italy from June 1986 to March 1987. The home range, estimated by the minimum convex polygon from 421 radio locations, measured 197 km² and comprised several infrastructures and areas of human presence, including four garbage dumps and two offal sites. Core areas, calculated by the harmonic mean method, were located toward the centre of the home range where human disturbance and road density were lowest but forest cover was highest. During the time-span of the study, home-range use and movement patterns suggested a marked centrality in spatial behaviour and traditionality in retreat areas year-round, both during pup-rearing season and the following months. In addition, by being essentially nocturnal, resident wolves appeared to adopt tactics of temporal segregation from people to exploit food resources safely in the proximity of human settlements. Overall activity correlated with distance travelled (r = 0.90, P << 0.001), and corresponded to cyclic nocturnal movements from retreat to feeding areas. Wolf movement rate between 20:00 and 04:00 h averaged 2.5 km/h but varied up to about 8 km/h, and daily distance travelled (= 27 km/night; range 17–38 km/night) mostly depended on the location of traditional feeding sites. Home-range configuration, habitat use, activity and movements all appeared highly integrated so as to represent the most functional compromise between avoidance of human inteference and exploitation of the available food resources.     

Home range size and activity of the wood lemming, Myopus schisticolor

We present the results from a radiotelemetric study on space use and activity in a natural population of the wood lemming Myopus schisticolor. Male home ranges were larger than females, and the ratio female home range to male home range was smaller than expected compared to other small rodents. Males moved distances 4-12 times longer than females. We argue that this difference in mobility gives a higher probability of capturing males than females in snap trap studies. If there is a sex biased trappability, this might explain the increasing female biased sex ratio during the snow free season (1:1 in spring, 3:1 [female:male| in autumn), as a higher mortality of males during the reproductive season.     

Movement,site fidelity and connectivity in a top marine predator,the killer whale

Movement, site fidelity and connectivity have important consequences for the evolution of population structure and therefore the conservation and management of a species. In this study photographs of naturally marked killer whales collected from sites across the Northeast Atlantic are used to estimate fidelity to sampling locations and movement between locations, expressed as transition probabilities, pt, using maximum likelihood methods. High transition probabilities suggest there is high inter-annual site fidelity to all locations, and large-scale movement between the spawning and wintering grounds of both Norwegian and Iceland stocks of Atlantic herring. There was no evidence of movement between the Norwegian herring grounds and Icelandic herring grounds, or between the mackerel fishing grounds and the herring fishing grounds. Thus the movement of predictable and abundant prey resources can lead to intrinsic isolation in this species We also find movement between the Northern Isles, Scotland and East Iceland. An association network indicates that killer whales predating seals around the Northern Isles, Scotland are linked to the community of killer whales that follow the Icelandic summer-spawning herring. This adds support to existing evidence of a broad niche width in some populations.     

Home range,habitat use,and activity patterns of free-roaming domestic cats

We used radio-telemetry and collar-mounted activity sensors to compare home range size, habitat use, and activity patterns of owned and unowned free-roaming cats on the outskirts of Champaign-Urbana, Illinois, USA. Owned cats (3 M, 8 F) had smaller home ranges than unowned cats (6 M, 10 F), but we failed to detect consistent differences in home range size between the sexes or among seasons. Home ranges of unowned cats included more grassland and urban area than predicted based on availability in all seasons, and farmsteads were selected in fall and winter. Within home ranges, unowned cats shifted their use of habitats among seasons in ways that likely reflected prey availability, predation risk, and environmental stress, whereas habitat use within home ranges by owned cats did not differ from random. Unowned cats were more nocturnal and showed higher overall levels of activity than owned cats. Space use and behavioral differences between owned and unowned cats supported the hypothesis that the care a cat owner provides influences the impact a cat has on its environment, information that is important for making decisions on controlling cat populations. © 2011 The Wildlife Society.     

Top-down population regulation of a top predator: lions in the Ngorongoro Crater

Efforts to determine whether bottom-up or top-down processes regulate populations have been hampered by difficulties in accurately estimating the population's carrying capacity and in directly measuring food intake rate, the impacts of interspecific competition and exposure to natural enemies. We report on 40 years of data on the lion population in Ngorongoro Crater, Tanzania, which showed strong evidence of density-dependent regulation at 100-120 individuals but has remained below 60 individuals for the past decade despite consistently high prey abundance. The lions enjoy a higher per capita food-intake rate and higher cub recruitment at low population density, and interspecific competition has not increased in recent years. These animals have suffered from a number of severe disease outbreaks over the past 40 years, but, whereas the population recovered exponentially from a severe epizootic in 1963, three outbreaks between 1994 and 2001 have occurred in such rapid succession that the population has been unable to return to the carrying capacity. The Crater population may have become unusually vulnerable to infectious disease in recent years owing to its close proximity to a growing human population and a history of close inbreeding. The Crater lions may therefore provide important insights into the future of many endangered populations.     

Friends and strangers: a test of the Charnov-Finerty Hypothesis

Summary We tested the hypothesis that populations composed of unrelated animals should perform worse than those composed of related animals by setting up two moderatedly dense field populations in adjacent enclosures: one was composed of related females and one of unrelated females; both had unrelated males. The survival and reproductive success of a number of litters located by spooling were determined. Final population size, pregnancy success, number of young recruited per pregnancy, and survival were similar in both populations. Thus, differences in relatedness produced no differences in demography. We conclude that the Charnov-Finerty Hypothesis in unlikely to be an explanation for microtine population fluctuations.     

Evolution of population structure in a highly social top predator, the killer whale

Intraspecific resource partitioning and social affiliations both have the potential to structure populations, though it is rarely possible to directly assess the impact of these mechanisms on genetic diversity and population divergence. Here, we address this for killer whales (Orcinus orca), which specialize on prey species and hunting strategy and have long-term social affiliations involving both males and females. We used genetic markers to assess the structure and demographic history of regional populations and test the hypothesis that known foraging specializations and matrifocal sociality contributed significantly to the evolution of population structure. We find genetic structure in sympatry between populations of foraging specialists (ecotypes) and evidence for isolation by distance within an ecotype. Fitting of an isolation with migration model suggested ongoing, low-level migration between regional populations (within and between ecotypes) and small effective sizes for extant local populations. The founding of local populations by matrifocal social groups was indicated by the pattern of fixed mtDNA haplotypes in regional populations. Simulations indicate that this occurred within the last 20,000 years (after the last glacial maximum). Our data indicate a key role for social and foraging behavior in the evolution of genetic structure among conspecific populations of the killer whale.     

Human-resource subsidies alter the dietary preferences of a mammalian top predator

Seasonal fitness declines are common, but the relative contribution of different reproductive components to the seasonal change in the production of reproductive young, and the component-specific drivers of this change is generally poorly known. We used long-term data (17 years) on breeding time (i.e. date of first egg laid) in northern wheatears (Oenanthe oenanthe) to investigate seasonal reproductive patterns and estimate the relative contributions of reproductive components to the overall decline in reproduction, while accounting for factors potentially linked to seasonal declines, i.e. individual and habitat quality. All reproductive components—nest success (reflecting nest predation rate), clutch size, fledging success and recruitment success—showed a clear decline with breeding time whereas subsequent adult survival did not. A non-linear increase in nest predation rate caused nest success to decline rapidly early in the season and level off at ~80 % success late in the breeding season. The combined seasonal decline in all reproductive components caused the mean production of recruits per nest to drop from around 0.7–0.2; with the relative contribution greatest for recruitment success which accounted for ~50 % of the decline. Our data suggest that changing environmental conditions together with effects of nest predation have strong effects on the seasonal decline in fitness. Our demonstration of the combined effects of all reproductive components and their relative contribution shows that omitting data from later stages of breeding (recruitment) can greatly underestimate seasonal fitness declines.     

Climate and density shape population dynamics of a marine top predator

Long-term studies have documented that climate fluctuations affect the dynamics of populations, but the relative influence of stochastic and density-dependent processes is still poorly understood and debated. Most studies have been conducted on terrestrial systems, and lacking are studies on marine systems explicitly integrating the fact that most populations live in seasonal environments and respond to regular or systematic environmental changes. We separated winter from summer mortality in a seabird population, the blue petrel Halobaena caerulea, in the southern Indian Ocean where the El Niño/Southern Oscillation effects occur with a 3-4-year lag. Seventy per cent of the mortality occurred in winter and was linked to climatic factors, being lower during anomalous warm events. The strength of density dependence was affected by climate, with population crashes occurring when poor conditions occurred at high densities. We found that an exceptionally long-lasting warming caused a ca. 40% decline of the population, suggesting that chronic climate change will strongly affect this top predator. These findings demonstrate that populations in marine systems are particularly susceptible to climate variation through complex interactions between seasonal mortality and density-dependent effects.