Disruption of an ant-plant mutualism shapes interactions between lions and their primary prey

Mutualisms often define ecosystems, but they are susceptible to human activities. Combining experiments, animal tracking, and mortality investigations, we show that the invasive big-headed ant (Pheidole megacephala) makes lions (Panthera leo) less effective at killing their primary prey, plains zebra (Equus quagga). Big-headed ants disrupted the mutualism between native ants (Crematogaster spp.) and the dominant whistling-thorn tree (Vachellia drepanolobium), rendering trees vulnerable to elephant (Loxodonta africana) browsing and resulting in landscapes with higher visibility. Although zebra kills were significantly less likely to occur in higher-visibility, invaded areas, lion numbers did not decline since the onset of the invasion, likely because of prey-switching to African buffalo (Syncerus caffer). We show that by controlling biophysical structure across landscapes, a tiny invader reconfigured predator-prey dynamics among iconic species.

“Ecology of fear” in ungulates: Opportunities for improving conservation

Because ungulates are important contributors to ecosystem function, understanding the “ecology of fear” could be important to the conservation of ecosystems. Although studying ungulate ecology of fear is common, knowledge from ungulate systems is highly contested among ecologists. Here, we review the available literature on the ecology of fear in ungulates to generalize our current knowledge and how we can leverage it for conservation. Four general focus areas emerged from the 275 papers included in our literature search (and some papers were included in multiple categories): behavioral responses to predation risk (79%), physiological responses to predation risk (15%), trophic cascades resulting from ungulate responses to predation risk (20%), and manipulation of predation risk (1%). Of papers focused on behavior, 75% were about movement and habitat selection. Studies were biased toward North America (53%), tended to be focused on elk (Cervus canadensis; 29%), and were dominated by gray wolves (40%) or humans (39%) as predators of interest. Emerging literature suggests that we can utilize predation risk for conservation with top‐down (i.e., increasing predation risk) and bottom‐up (i.e., manipulating landscape characteristics to increase risk or risk perception) approaches. It is less clear whether fear‐related changes in physiology have population‐level fitness consequences or cascading effects, which could be fruitful avenues for future research. Conflicting evidence of trait‐mediated trophic cascades might be improved with better replication across systems and accounting for confounding effects of ungulate density. Improving our understanding of mechanisms modulating the nature of trophic cascades likely is most important to ensure desirable conservation outcomes. We recommend future work embrace the complexity of natural systems by attempting to link together the focal areas of study identified herein.

Borrowing from Peter to pay Paul: managing threatened predators of endangered and declining prey species

Conservation policy and practice can sometimes run counter to their mutual aims of ensuring species survival. In Kenya, where threatened predators such as lion deplete endangered prey such as Grevy's zebra, conservation practitioners seek to ensure species success through exclusive strategies of protection, population increase and preservation. We found strong selection for the endangered Grevy's zebra by both lion and hyena on two small fenced conservancies in Kenya. Despite abundant diversity of available prey, Grevy's zebra were selected disproportionately more than their availability, while other highly available species such as buffalo were avoided. Lions were therefore not alone in presenting a credible threat to Grevy's zebra survival. Conservation practitioners must consider interlinked characteristics of prey selection, resource availability and quality, the interplay between carnivore guild members and landscape scale population trends performance in wildlife management decisions.

Advances in population ecology and species interactions in mammals

The study of mammals has promoted the development and testing of many ideas in contemporary ecology. Here we address recent developments in foraging and habitat selection, source–sink dynamics, competition (both within and between species), population cycles, predation (including apparent competition), mutualism, and biological invasions. Because mammals are appealing to the public, ecological insight gleaned from the study of mammals has disproportionate potential in educating the public about ecological principles and their application to wise management. Mammals have been central to many computational and statistical developments in recent years, including refinements to traditional approaches and metrics (e.g., capture-recapture) as well as advancements of novel and developing fields (e.g., spatial capture-recapture, occupancy modeling, integrated population models). The study of mammals also poses challenges in terms of fully characterizing dynamics in natural conditions. Ongoing climate change threatens to affect global ecosystems, and mammals provide visible and charismatic subjects for research on local and regional effects of such change as well as predictive modeling of the long-term effects on ecosystem function and stability. Although much remains to be done, the population ecology of mammals continues to be a vibrant and rapidly developing field. We anticipate that the next quarter century will prove as exciting and productive for the study of mammals as has the recent one.

Resolving a conservation dilemma: Vulnerable lions eating endangered zebras

When predators are removed or suppressed for generations, prey populations tend to increase and when predators are re-introduced, prey densities should fall back to pre-control levels. In cases of apparent competition where there are alternate abundant and rare prey species, rare species may decline further than expected or disappear altogether. Recently, concern about the impact of recovering predator populations on wildlife in Laikipia County, Kenya, has led to questions of whether lions (Panthera leo, IUCN Red List Vulnerable) exert top-down pressure on Grevy's zebra (Equus grevyi, IUCN Red List Endangered). We examined effects of lion predation on Plain's zebra (E. quagga, IUCN Red List Near Threatened) and Grevy's zebra populations in a 2,105 km2 area defined by lion movements. We used line transect surveys to estimate density of Grevy's (0.71/km2) and Plain's (15.9/km2) zebras, and satellite telemetry to measure movements for lions and both zebras. We tracked lions to potential feeding sites to estimate predation rates on zebras. We compared field-based estimates of predation rates on both zebras to random gas models of encounters that result in predation to ask if lions prey preferentially on Grevy's zebra at a sufficient rate to drive population declines. Lions preyed on Grevy's zebra significantly less than expected in 15 of 16 (94%) scenarios considered and lions preyed on Plain's zebras as expected or significantly less than expected in 15 of 16 scenarios. Population trend of Grevy's zebra indicates that the Kenya population may be stabilizing. Recruitment rate to the population has tripled since 2004, making it unlikely that lions are having an impact on Grevy's zebras. In Laikipia County, competitive displacement by livestock (Livestock: Grevy's zebra ratio = 864:1) and interference competition for grass with Plain's zebra (Plain's zebra:Grevy's zebra ratio = 22:1) are most likely the predominant threats to Grevy's Zebra recovery.

Demographic drivers of a refugee species: large-scale experiments guide strategies for reintroductions of hirola

Effective reintroduction strategies require accurate estimates of vital rates and the factors that influence them. The hirola (Beatragus hunteri) is the rarest antelope on Earth, with a global population size of <500 individuals restricted to the Kenya-Somali border. We estimated vital rates of hirola populations exposed to varying levels of predation and rangeland quality from 2012 to 2015, and then built population matrices to estimate the finite rate of population change (λ) and demographic sensitivities. Mean survival for all age classes and population growth was highest in the low-predation-high-rangeland-quality setting (λ = 1.08 ± 0.03 [mean ± SE]), and lowest in the high-predation-low-rangeland-quality setting (λ = 0.70 ± 0.22). Retrospective demographic analyses revealed that increased fecundity (the number of female calves born to adult females annually) and female calf survival were responsible for higher population growth where large carnivores were absent. In contrast, variation in adult female survival was the primary contributor to differences in population growth attributable to rangeland quality. Our analyses suggest that hirola demography is driven by a combination of top-down (predation) and bottom-up (rangeland quality) forces, with populations in the contemporary geographic range impacted both by declining rangeland quality and predation. To enhance the chances of successful reintroductions, conservationists can consider rangeland restoration to boost both the survival and fecundity of adult females within the hirola's historical range.