Conservation and Ecology of Mammals IV

Contributed Paper
ROOM: Room 120 – Dona Ana

10:30AM Floods to Fire: Evaluating Sitatunga Space-Use During Varying Hydrologic Conditions
Camille H. Warbington; Mark S. Boyce
Across sub-Saharan Africa, freshwater wetlands serve as primary habitat for sitatunga (Tragelaphus spekii), a spiral-horned antelope species. Previous studies of sitatunga hypothesized, but did not quantitatively assess, that sitatunga avoid areas used by cattle, and used wetland habitats longer distances from shorelines during dry seasons and droughts. However, none of the previous studies occurred in wetlands dominated by papyrus (Cyperus papyrus), nor did they address habitat use during flood or high-water conditions. Beginning in 2015, we placed camera traps in three different habitat types in a papyrus wetland along the Mayanja River in central Uganda – wetlands adjacent to shorelines, wetlands along river channels, and dry land in gallery forests. In 2016, the Mayanja River area experienced a flood event, and in 2017 a severe drought predisposed a portion of the wetland to wildfire. We assessed the number of sitatunga encounters, other terrestrial vertebrate wildlife species (OTV) encounters, and human and livestock encounters per trap day in the three site types during normal (2015), flood (2016), and drought (2017) conditions. We tested for differences in the proportions of detections between hydrologic conditions using a modified Chi-squared statistic. Detections of sitatunga were significantly lower in the flood year compared to normal conditions for all types of sites. In contrast, detections of OTV in gallery forest habitats was substantially higher in flood conditions than during normal water levels, and had the opposite trend in their use of shoreline wetlands. Preliminary results suggest that drought conditions lead to increases in use of shoreline wetlands by cattle and OTV, and a decrease in use of shorelines by sitatunga. As climate change and human populations place pressure on wetlands, understanding the magnitude of sitatunga reliance on wetlands and their tolerance of livestock is crucial for effective management of the species.
10:50AM Savanna Elephant Numbers Are Only a Quarter of Their Expected Values
Ashley S. Robson; Morgan J. Trimble; Andrew Purdon; Kim Young-Overton; Stuart L. Pimm; Rudi J. van Aarde
Savannas once constituted the range of many species that human encroachment has now reduced to a fraction of their former distribution. Many survive only in protected areas. Poaching reduces the savanna elephant (Loxodonta africana), even where protected, likely to the detriment of savanna ecosystems. While resources go into estimating elephant populations, an ecological benchmark by which to assess counts is lacking. Knowing how many elephants there are and how many poachers kill is important, but on their own, such data lack context. We collated savanna elephant count data from 73 protected areas across the continent estimated to hold ~50% of Africa’s elephants and extracted densities from 18 broadly stable population time series. We modeled these densities using primary productivity, water availability, and an index of poaching as predictors. We then used the model to predict stable densities given current conditions and poaching for all 73 populations. Next, to generate ecological benchmarks, we predicted such densities for a scenario of zero poaching. Where historical data are available, they corroborate or exceed benchmarks. According to recent counts, collectively, the 73 savanna elephant populations are at 75% of the size predicted based on current conditions and poaching levels. However, populations are at <25% of ecological benchmarks given a scenario of zero poaching (~967,000)—a total deficit of ~730,000 elephants. Populations in 30% of the 73 protected areas were <5% of their benchmarks, and the median current density as a percentage of ecological benchmark across protected areas was just 13%. The ecological context provided by these novel benchmark values, in conjunction with ongoing census projects, allow efficient targeting of conservation efforts. Additionally, the model could be used as a management tool under future scenarios of water supplementation and climate change.
11:10AM Spatiotemporal Dynamics in Space Use of Mongolian Gazelle: Conservation Implication of Nomadic Movements
Nandintsetseg Dejid; Chloe Bracis; Kirk Olson; Thomas Mueller
Unlike residency and migration, long distance nomadic movements of terrestrial mammals are little understood and conservation strategies for these animals are largely missing. Here, we studied spatiotemporal variability of space use of nomadic Mongolian gazelle (Procapra gutturosa) and conservation implications of their movements using GPS data of 25 individuals tracked from 6 months to over two years. We found a high degree of variability in space use among individuals within a year and also significant variability within individuals between years, where the same individuals often showed entirely different wintering areas between years. On average, single gazelle covered an area of ~22,000 km2 in one year and ~31,000 km2 in two years. A mere eight individuals that were caught at the same day and location and that were tracked over two years occupied an area of ~93,000 km2 (roughly the size of Indiana). Moreover, simulation experiments showed that gazelles avoided areas with high disturbances (e.g. oil fields, population centers). They also demonstrated that there was no particular preference for protected areas – although individuals moved through a total of six protected areas. In addition, border fences were an impermeable barrier for the gazelles’ movements and the average distance moved along these fences before giving up crossing them was 23 km. Our findings highlight that gazelles roam over large ranges that are highly variable in space and time indicating that landscape permeability is essential to sustain their movements. In addition, border fences obstructed the long-distance movements of gazelles and overall, linear barriers that are currently planned or under construction could pose the most significant risk to the integrity of the gazelles’ movement. Therefore, our findings recommend that new linear structures need to have frequent crossing options to mitigate disturbances to gazelle movements and to maintain landscape permeability.
11:30AM Movement Ecology, Habitat, and Nutrient Transfer Dynamics of the Common Hippopotamus
Tristan Nunez; Douglas J. McCauley; Justin Brashares
The common hippopotamus (Hippopotamus amphibius) is a vulnerable megaherbivore and keystone species that transports nutrients between the terrestrial and aquatic ecosystems of Africa. Its movements have never before been electronically tracked, so little is known about its basic movement behavior, habitat and space utilization, or the landscapes of biomass removal and deposition it creates. We tracked 13 individual H. amphibius in the Ewaso Ng’iro river in Kenya with GPS and accelerometer units at high temporal resolutions. We calculated the size, shape, and topographical and vegetation correlates of H. amphibius home ranges and habitat use using the GPS tracking data. H. amphibius movements on land are structured around pools used as thermal refuges during the day and grazing lawns exploited at night. In addition to describing basic movement and space use metrics useful for conservation planning, we quantified space and time budgets for different behavioral states, using this information to develop a spatially explicit biomass transfer model to map and described the spatial heterogeneity of the removal, deposition, and net transfer of biomass by H. amphibius. This mapping effort revealed biomass transfer hotspots arising from H. amphibius movements both in water and on land. Advances in tracking technologies provide an opportunity to greatly increase understanding of the spatial patterns of nutrient transfers from mobile organisms at ecologically relevant resolutions, helping understand the potential landscape- and ecosystem-level consequences of range-wide declines in distribution and abundance of H. amphibius in the last century.
11:50AM Ecosystem Engineering by Subterranean Insects Buffers Large Mammals Against Climate Warming
Ryan Long; Elyce Gosselin; Savannah Kollasch; Warren P. Porter; Robert M. Pringle
Tropical savannas support the most diverse assemblages of large-bodied mammals on earth, and also are commonly occupied by colonies of mound-building termites. These subterranean insects concentrate nutrients and water, which leads to dense, nutrient-rich vegetation on and/or around mounds. In addition to serving as “resource hotspots,” nest structures and associated vegetation generate heterogeneity in the thermal landscape that may be important for buffering large, heat-sensitive mammals against the energetic costs of rising environmental temperatures. We used a mechanistic model of heat and mass transfer to evaluate the importance of termite mounds as thermal refugia under current and future climate scenarios for three congeneric antelope species that varied five-fold in body size: kudu (Tragelaphus strepsiceros), nyala (T. angasii), and bushbuck (T. scriptus). Rates of evaporative water loss necessary to maintain homeothermy were significantly higher in matrix habitat than on mounds for all three species. However, the proportional reduction in water loss conferred by using mounds increased with body size. Similarly, under simulated climate-warming scenarios, the cost of using matrix habitat increased more rapidly than the cost of using mounds, and this discrepancy was most pronounced for larger species. Our results suggest that the importance of termite mounds as thermal refugia will increase considerably as global temperatures rise, but that the benefits of using mounds will accrue disproportionately to larger-bodied species. This could have important implications for competition and niche partitioning in size-structured communities of large mammals.


Contributed Paper
Location: Albuquerque Convention Center Date: September 27, 2017 Time: 10:30 am - 12:10 pm