Scholarly Work - Ecology

Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/8716

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Carnivores, competition and genetic connectivity in the Anthropocene
(2019-11) Creel, Scott; Spong, Goran; Becker, Matthew S.; Simukonda, Chuma; Norman, Anita; Schiffthaler, Bastian; Chifunte, Clive
Current extinction rates are comparable to five prior mass extinctions in the earth’s history, and are strongly affected by human activities that have modified more than half of the earth’s terrestrial surface. Increasing human activity restricts animal movements and isolates formerly connected populations, a particular concern for the conservation of large carnivores, but no prior research has used high throughput sequencing in a standardized manner to examine genetic connectivity for multiple species of large carnivores and multiple ecosystems. Here, we used RAD SNP genotypes to test for differences in connectivity between multiple ecosystems for African wild dogs (Lycaon pictus) and lions (Panthera leo), and to test correlations between genetic distance, geographic distance and landscape resistance due to human activity. We found weaker connectivity, a stronger correlation between genetic distance and geographic distance, and a stronger correlation between genetic distance and landscape resistance for lions than for wild dogs, and propose a new hypothesis that adaptations to interspecific competition may help to explain differences in vulnerability to isolation by humans.
Foraging investment in a long-lived herbivore and vulnerability to coursing and stalking predators
(2018-10) Christianson, David A.; Becker, Matthew S.; Brennan, Angela; Creel, Scott; Droge, Egil; M'soka, Jassiel; Mukula, Teddy; Schuette, Paul; Smit, Daan; Watson, Fred
Allocating resources to growth and reproduction requires grazers to invest time in foraging, but foraging promotes dental senescence and constrains expression of proactive antipredator behaviors such as vigilance. We explored the relationship between carnivore prey selection and prey foraging effort using incisors collected from the kills of coursing and stalking carnivores. We predicted that prey investing less effort in foraging would be killed more frequently by coursers, predators that often exploit physical deficiencies. However, such prey could expect delayed dental senescence. We predicted that individuals investing more effort in foraging would be killed more frequently by stalkers, predators that often exploit behavioral vulnerabilities. Further these prey could expect earlier dental senescence. We tested these predictions by comparing variation in age-corrected tooth wear, a proxy of cumulative foraging effort, in adult (3.4-11.9 years) wildebeest killed by coursing and stalking carnivores. Predator type was a strong predictor of age-corrected tooth wear within each gender. We found greater foraging effort and earlier expected dental senescence, equivalent to 2.6 additional years of foraging, in female wildebeest killed by stalkers than in females killed by coursers. However, male wildebeest showed the opposite pattern with the equivalent of 2.4 years of additional tooth wear in males killed by coursers as compared to those killed by stalkers. Sex-specific variation in the effects of foraging effort on vulnerability was unexpected and suggests that behavioral and physical aspects of vulnerability may not be subject to the same selective pressures across genders in multipredator landscapes.
Quantifying lion (Panthera leo) demographic response following a three-year moratorium on trophy hunting.
(2018-05) Mweetwa, Thandiwe; Christianson, David A.; Becker, Matthew S.; Creel, Scott; Rosenblatt, Elias G.; Merkle, Johnathan; Droge, Egil; Mwape, Henry; Masonde, Jones; Simpamba, Twakundine
Factors that limit African lion populations are manifold and well-recognized, but their relative demographic effects remain poorly understood, particularly trophy hunting near protected areas. We identified and monitored 386 individual lions within and around South Luangwa National Park, Zambia, for five years (2008-2012) with trophy hunting and for three additional years (2013-2015) during a hunting moratorium. We used these data with mark-resight models to estimate the effects of hunting on lion survival, recruitment, and abundance. The best survival models, accounting for imperfect detection, revealed strong positive effects of the moratorium, with survival increasing by 17.1 and 14.0 percentage points in subadult and adult males, respectively. Smaller effects on adult female survival and positive effects on cub survival were also detected. The sex-ratio of cubs shifted from unbiased during trophy-hunting to female-biased during the moratorium. Closed mark-recapture models revealed a large increase in lion abundance during the hunting moratorium, from 116 lions in 2012 immediately preceding the moratorium to 209 lions in the last year of the moratorium. More cubs were produced each year of the moratorium than in any year with trophy hunting. Lion demographics shifted from a male-depleted population consisting mostly of adult (â‰¥4 years) females to a younger population with more (>29%) adult males. These data show that the three-year moratorium was effective at growing the Luangwa lion population and increasing the number of adult males. The results suggest that moratoria may be an effective tool for improving the sustainability of lion trophy hunting, particularly where systematic monitoring, conservative quotas, and age-based harvesting are difficult to enforce.
Opposing effects of group size on reproduction and survival
(2015-07) Creel, Scott; Creel, Nancy M.
For cooperative breeders, we hypothesize that the effects of group size on reproduction and survival might run in opposition if the benefits of grouping cannot be shared without cost. We tested this hypothesis by examining relationships between group size, survival, and reproduction in African wild dogs (Lycaon pictus), cooperative hunters with highly cohesive packs within which reproduction is monopolized by the dominant male and female. The production and survival of pups are known to increase with increasing pack size, but the effect of pack size on adult survival has not been examined previously. Data from 366 individuals over a period of 6 years showed that the survival of adults decreased with increasing pack size, with a 25% difference between the largest and smallest packs after controlling for the effects of age, sex, social status, year of study, and pack identity. Several tests confirmed that undetected dispersal is unlikely to have produced this pattern. These results suggest that cooperative breeding in wild dogs cannot be fully explained by mutual direct benefit, thus reinforcing the prior inference that kin selection plays an important role in the evolution of their cooperation. The results also weaken support for the hypothesis that wild dogs are extinction prone due to group-level Allee effects. More broadly, the relationship of effects of group size on survival and reproduction might be predicted by considering whether cooperation yields benefits that accrue to all group members (e.g., through cooperative vigilance) or benefits that must be apportioned to individuals (e.g., through cooperative hunting).
The relationship between direct predation and antipredator responses: a test with multiple predators and multiple prey
(2017-08) Creel, Scott; M'soka, Jassiel; Smit, Daan; Becker, Matthew S.; Christianson, David A.; Schuette, Paul; Dröge, Egil
Most species adjust their behavior to reduce the likelihood of predation. Many experiments have shown that antipredator responses carry energetic costs that can affect growth, survival, and reproduction, so that the total cost of predation depends on a trade-off between direct predation and risk effects. Despite these patterns, few field studies have examined the relationship between direct predation and the strength of antipredator responses, particularly for complete guilds of predators and prey. We used scan sampling in 344 observation periods over a four-year field study to examine behavioral responses to the immediate presence of predators for a complete antelope guild (dominated by wildebeest, zebra, and oribi) in Liuwa Plains National Park, Zambia, testing for differences in response to all large carnivores in the ecosystem (lions, spotted hyenas, cheetahs, and African wild dogs). We quantified the proportion that each prey species contributed to the kills made by each predator (516 total kills), used distance sampling on systematic line transects to determine the abundance of each prey species, and combined these data to quantify the per-capita risk of direct predation for each predator-prey pair. On average, antelopes increased their vigilance by a factor of 2.4 when predators were present. Vigilance varied strongly among prey species, but weakly in response to different predators. Increased vigilance was correlated with reduced foraging in a similar manner for all prey species. The strength of antipredator response was not detectably related to patterns of direct predation (n = 15 predator-prey combinations with sufficient data). This lack of correlation has implications for our understanding of the role of risk effects as part of the limiting effect of predators on prey.
Spatial and temporal avoidance of risk within a large carnivore guild
(2017-01) Droge, Egil; Creel, Scott; Becker, Matthew S.; M'soka, Jassiel
Within a large carnivore guild, subordinate competitors (African wild dog, Lycaon pictus, and cheetah, Acinonyx jubatus) might reduce the limiting effects of dominant competitors (lion, Panthera leo, and spotted hyena, Crocuta crocuta) by avoiding them in space, in time, or through patterns of prey selection. Understanding how these competitors cope with one other can inform strategies for their conservation. We tested how mechanisms of niche partitioning promote coexistence by quantifying patterns of prey selection and the use of space and time by all members of the large carnivore guild within Liuwa Plain National Park in western Zambia. Lions and hyenas specialized on wildebeest, whereas wild dogs and cheetahs selected broader diets including smaller and less abundant prey. Spatially, cheetahs showed no detectable avoidance of areas heavily used by dominant competitors, but wild dogs avoided areas heavily used by lions. Temporally, the proportion of kills by lions and hyenas did not detectably differ across four time periods (day, crepuscular, early night, and late night), but wild dogs and especially cheetahs concentrated on time windows that avoided nighttime hunting by lions and hyenas. Our results provide new insight into the conditions under which partitioning may not allow for coexistence for one subordinate species, the African wild dog, while it does for cheetah. Because of differences in responses to dominant competitors, African wild dogs may be more prone to competitive exclusion (local extirpation), particularly in open, uniform ecosystems with simple (often wildebeest dominated) prey communities, where spatial avoidance is difficult.
Energy Landscapes and the Landscape of Fear
(2017-02) Gallagher, Austin J.; Creel, Scott; Wilson, Rory P.; Cooke, Steven J.
Animals are not distributed randomly in space and time because their movement ecology is influenced by a variety of factors. Energy landscapes and the landscape of fear have recently emerged as largely independent paradigms, both reshaping our perspectives and thinking relating to the spatial ecology of animals across heterogeneous landscapes. We argue that these paradigms are not distinct but rather complementary, collectively providing a better mechanistic basis for understanding the spatial ecology and decision-making of wild animals. We discuss the theoretical underpinnings of each paradigm and illuminate their complementary nature through case studies, then integrate these concepts quantitatively by constructing quantitative pathways of movement modulated by energy and fear to elucidate the mechanisms underlying the spatial ecology of wild animals.
The many effects of carnivores on their prey and their implications for trophic cascades, and ecosystem structure and function
(2016-09) Winnie, John A. Jr.; Creel, Scott
Despite some controversy, a wide range of research across multiple taxa have established that carnivores strongly influence prey population dynamics both through direct offtake and indirect risk effects. Because of these powerful top-down effects carnivores can influence ecosystems across multiple trophic levels. Here we discuss research addressing carnivore direct- and indirect effects on prey, and how these effects can influence overall ecosystem structure and function.
Hunting on a hot day: effects of temperature on interactions between African wild dogs and their prey
(2016-11) Creel, Scott; Creel, Nancy M.; Creel, Andrea M; Creel, Bridget
As global temperatures increase, interactions between species are affected by changes in distribution, abundance and phenology, but also by changes in behavior. The heat dissipation limitation hypothesis suggests that the ability to dissipate heat commonly limits the activity of endotherms, a problem that should be particularly acute for cursorial predators and their prey in equatorial ecosystems. Allometric relationships suggest that heat dissipation should be a stronger constraint for larger species, so that (smaller) predators should be less affected than (larger) prey. We used data from 266 complete days of direct observation of African wild dogs (Lycaon pictus) in five packs over a period of 2 yr to test how deviations of temperature from that expected for the time of day affected eight measures of hunting effort and success. We found that higher temperatures disadvantaged the prey of wild dogs more than the dogs themselves, with increased hunting success and shorter pursuits on warmer days. Broadly, our results demonstrate that effects of temperature on behavior can alter interactions between species, exacerbating or offsetting the direct effects of climate change.
Effects of a protection gradient on carnivore density and survival: an example with leopards in the Luangwa valley, Zambia
(2016-06) Rosenblatt, Elias G.; Creel, Scott; Becker, Matthew S.; Merkle, Johnathan; Mwape, Henry; Schuette, Paul; Simpamba, Twakundine
Human activities on the periphery of protected areas can limit carnivore populations, but measurements of the strength of such effects are limited, largely due to difficulties of obtaining precise data on population density and survival. We measured how density and survival rates of a previously unstudied leopard population varied across a gradient of protection and evaluated which anthropogenic activities accounted for observed patterns. Insights into this generalist's response to human encroachment are likely to identify limiting factors for other sympatric carnivore species. Motion-sensitive cameras were deployed systematically in adjacent, similarly sized, and ecologically similar study areas inside and outside Zambia's South Luangwa National Park (SLNP) from 2012 to 2014. The sites differed primarily in the degree of human impacts: SLNP is strictly protected, but the adjacent area was subject to human encroachment and bushmeat poaching throughout the study, and trophy hunting of leopards prior to 2012. We used photographic capture histories with robust design capture-recapture models to estimate population size and sex-specific survival rates for the two areas. Leopard density within SLNP was 67% greater than in the adjacent area, but annual survival rates and sex ratios did not detectably differ between the sites. Prior research indicated that wire-snare occurrence was 5.2 times greater in the areas adjacent to the park. These results suggest that the low density of leopards on the periphery of SLNP is better explained by prey depletion, rather than by direct anthropogenic mortality. Long-term spatial data from concurrent lion studies suggested that interspecific competition did not produce the observed patterns. Large carnivore populations are often limited by human activities, but science-based management policies depend on methods to rigorously and quantitatively assess threats to populations of concern. Using noninvasive robust design capture-recapture methods, we systematically assessed leopard density and survival across a protection gradient and identified bushmeat poaching as the likely limiting factor. This approach is of broad value to evaluate the impacts of anthropogenic activities on carnivore populations that are distributed across gradients of protection.

Scholarly Work - Ecology

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