Christian Kiffner

Lion populations may be declining in Africa but not as Bauer et al. suggest

Historical knowledge and recent surveys attest that lions are declining across parts of Africa (1, 2). We applaud Bauer et al. (3) for assembling available counts because they motivate better monitoring and conservation support. Their own data, however, rejects their claims that lions are “declining everywhere, except in four southern countries” and that lions increase only where “intensively managed.”

Bushmeat Consumption in the Tarangire-Manyara Ecosystem, Tanzania

Illegal hunting, driven by demand for bushmeat, threatens animal populations throughout Africa. While bushmeat consumption is thought to be common in the Tarangire-Manyara ecosystem (TME) of Northern Tanzania, its magnitude and drivers are not well understood. This lack of knowledge may inhibit effective mitigation policies. We conducted 394 household interviews in the TME in 2013 and 2014 to assess both the scale and the possible drivers of bushmeat availability and consumption in the ecosystem. Using generalized linear mixed models, information theoretic model selection, and accounting for spatial clustering of the interviews, we tested multiple hypotheses that underlie bushmeat consumption. Bushmeat consumption in the TME was found to be widespread among the local population. Surprisingly, we found little differences in reported bushmeat consumption between survey years (2013: 38%; 2014: 33% of interviewees). Pastoral Maasai admitted to consuming bushmeat significantly less often (2013: 29%; 2014: 26%) than non-Maasai (2013: 38%; 2014: 34%). Interestingly, none of the hypothesized spatial- or household-level factors consistently correlated with reported bushmeat consumption. Neither alternative sources of available animal protein, nor relative wealth affected bushmeat consumption. In conjunction with the relatively low price of bushmeat (half the price of domestic meat), these results suggest that bushmeat consumption is largely driven by its availability and low cost, and only to a small degree by cultural differences. Thus, conservation interventions will likely be most successful if they holistically manage to increase the cost of bushmeat relative to alternative protein sources.

Seasonal Patterns of Mixed Species Groups in Large East African Mammals

Mixed mammal species groups are common in East African savannah ecosystems. Yet, it is largely unknown if co-occurrences of large mammals result from random processes or social preferences and if interspecific associations are consistent across ecosystems and seasons. Because species may exchange important information and services, understanding patterns and drivers of heterospecific interactions is crucial for advancing animal and community ecology. We recorded 5403 single and multi-species clusters in the Serengeti-Ngorongoro and Tarangire-Manyara ecosystems during dry and wet seasons and used social network analyses to detect patterns of species associations. We found statistically significant associations between multiple species and association patterns differed spatially and seasonally. Consistently, wildebeest and zebras preferred being associated with other species, whereas carnivores, African elephants, Maasai giraffes and Kirks dik-diks avoided being in mixed groups. During the dry season, we found that the betweenness (a measure of importance in the flow of information or disease) of species did not differ from a random expectation based on species abundance. In contrast, in the wet season, we found that these patterns were not simply explained by variations in abundances, suggesting that heterospecific associations were actively formed. These seasonal differences in observed patterns suggest that interspecific associations may be driven by resource overlap when resources are limited and by resource partitioning or anti-predator advantages when resources are abundant. We discuss potential mechanisms that could drive seasonal variation in the cost-benefit tradeoffs that underpin the formation of mixed-species groups.

Abundance estimations of ixodid ticks on Boran cattle and Somali sheep in Northern Tanzania

ABSTRACT Assessing tick abundance on live animals is often required for management or research purposes, but tick counts on the entire body are time-consuming. In order to develop models to estimate tick abundance on the entire body of an animal by counting ticks on only one or two body parts, we counted ticks on one lateral side of Boran cattle (n = 44) and Somali sheep (n = 20) in Manyara Ranch, Northern Tanzania. Ticks were counted on nine distinct body parts (head, ears, neck, forelegs, abdomen, udder/groin, hind legs, perineum and rest of body). A total of 2559 ticks representing 10 species were collected from the two livestock species. For cattle, tick counts on the combined head (head and ear) constituted 32.02% of total ticks per animal, and were positively and significantly correlated with tick abundance on the entire host animal. In sheep, tick counts on the head (constituting 32.48% of all ticks on a host) and head including the ears (48.08%) were also highly correlated with tick abundance on the entire body. Linear regression models were established to estimate total tick abundance for cattle and sheep based on tick counts on the head and ears. These models had high predictive power (cattle: R2 = 0.71; sheep: R2 = 0.88) and thus appear to reliably estimate tick abundance on a given host individual. These models allow for much quicker collection time in assessing tick abundance under field conditions and hence reduce examination-related stress to the animal.

Performance of ground-based and aerial survey methods for monitoring wildlife assemblages in a conservation area of northern Tanzania

Validating and improving field-sampling techniques for estimating wildlife community composition and population size is essential for wildlife management and conservation. We conducted ground distance sampling surveys along line transects and block counts from a small aircraft in Manyara Ranch in Northern Tanzania and contrasted estimates of species richness and species-specific densities from both sampling techniques. We used regression analyses (logistic regression and generalized linear mixed models) and model selection to investigate whether a species’ body size, group size, body color, as well as vegetation cover explained the variation in species presence/absence and relative density differences in aerial vs. ground-based sampling. Ground surveys detected significantly more species than aerial surveys. However, aerial surveys detected three species that were missed by ground surveys (African lions, African buffalo, and spotted hyena). Model selection suggested that species with smaller body mass and small group sizes were more likely to be missed in aerial surveys. Densities estimated from the aerial surveys were generally but non-significantly lower than the densities estimated from the ground surveys, with the exception of density estimates for African elephants which were slightly higher from aerial surveys. Density differences between the two methods were greater for species with small group size, light body color, and in areas with denser vegetation cover; these variables explained 75% of the variation in density differences between the two survey methods. Albeit being similar in operational costs in our relatively small study area, ground surveys yielded (1) more complete information with respect to wildlife community composition and (2) density estimates were mostly higher and (3) more precise and (4) appear more feasible to be implemented in community-based conservation schemes.

Long‐term population dynamics in a multi‐species assemblage of large herbivores in East Africa

Wildlife population declines in Africa are widespread. However, species-specific population trends and dynamics in mammal community composition have rarely been described over long time periods. To describe population trends of 13 large herbivore species in Lake Manyara National Park (Tanzania) from 1959 to 2016 and to discover whether the herbivore community structure changed, we used general additive models and additional statistical methods to detect structural changes in the time series. Population dynamics were non-linear and population growth rates were not correlated with precipitation anomalies. Relatively steep population declines of three megaherbivores occurred during the 1980s and early 1990s, resulting in severe reductions in African elephant and buffalo populations and the local extinction of black rhinoceros. These declines coincided with reported peaks of illegal hunting of these species and expansion of agriculture at the periphery of the park. Population densities of elephant and buffalo seem to have stabilized in recent times, yet have not recovered to previous densities. In contrast, eight species (giraffe, zebra, waterbuck, wildebeest, warthog, impala, bushbuck, and baboon) have apparently fared well (similar or higher densities in most recent compared to first decade), despite having undergone substantial fluctuations over the past 58 yr. Population fluctuations in these species were likely caused by disease outbreaks, heavy bush encroachment, and reduced competition with buffalo. Possibly, declines in megaherbivore densities (mainly elephants) facilitated bush encroachment. Albeit grazers are still dominating in the herbivore community, the proportion of browsers is currently increasing, likely encouraged by dense vegetation in the shrub layer in large parts of the park. Overall, herbivore biomass density has declined by ~40% compared to the baseline estimate in the first decade of the time series. Our analyses and ancillary information provide evidence that this overall decline in the herbivore assemblage was triggered by human-induced reductions in megaherbivore population densities during the 1980s, either through excessive poaching, insularization of the park, or both. Likely, this had cascading and interacting effects on the vegetation structure and the herbivore assemblage. Thus, legacy effects of ineffective megaherbivore conservation efforts 30 yr ago are likely still affecting the ecology of this national park.