Animal assemblages are often viewed as a product of the ecosystems in which they live, but in reality they are often the reason an ecosystem looks the way it does. The roles of animals in shaping ecosystems are so important that two special issues recently published in PNAS and Ecography focus specifically on megafauna (literately translated as ‘large animal’) and the important roles they play in ecosystems, as well as what we may have lost through their extinctions across much of the globe.
Such large-bodied animals perform critical ecosystem roles, ranging from nutrient dispersal to altering the composition and structure of vegetation communities. However, it is not only large animals that perform these roles. Small bodied invertebrates are also crucial, sometimes even more so. Termites, for example, influence and control many ecosystem processes in the tropics and sub-tropics, including decomposition, nutrient cycling and soil hydrological processes, with wide ranging effects on vegetation and animal communities.
The CAO image above shows how woody vegetation (red color) is greatly reduced by large-bodied herbivores outside an exclosure area (upper part of the picture) in South Africa’s Kruger National Park.
The Carnegie Airborne Observatory (CAO) investigates the roles both large and small animals play in ecosystems, to answer questions at landscapes scales that were extremely difficult, if not impossible, to adequately address before. Although perhaps better known for our vegetation-based studies, a persistent and growing branch of the CAO is focused on animals, studying both their impacts on ecosystems and how ecosystems and their associated vegetation affect animal dynamics. CAO team members and collaborators seek to answer pertinent questions about how to conserve the dwindling numbers of many species, including the critical role of protected areas in this objective. These areas are in many ways the arks of the future, acting as the last remaining strongholds for many species. However, management of animals within them can be highly complex giving their smaller size compared to fully natural ecosystems.
Previous CAO animal ecology studies span a very wide range of animal body sizes, and encompass a large variety of related ecosystem processes. Several studies have investigated the role termites play in controlling soil nutrients and vegetation in African savannas, with far reaching implications for mammalian herbivores. By mapping termite mounds with LiDAR, CAO scientists have found that termites can alter as much as 20% of savanna landscapes, affecting the distribution of grasses and trees, and the foraging behavior of megaherbivores. Without the remote sensing technology, the far reaching effects termites have could well have been missed or underestimated.
The image on the left shows how termite mounds mapped with CAO LiDAR stand out from the surrounding terrain, while the right picture shows herbivores foraging on termite mound vegetation.
On the other end of the animal size scale, CAO studies have measured the impacts of elephants on savanna ecosystems. In a recent study published in the Ecography megafauna special issue, elephants in South Africa’s Kruger National Park where found to be the main determinant of treefall, outweighing all other investigated factors, including fire and natural mortality. Elephant numbers are falling in much of Africa, but the Kruger population has been growing at a remarkable rate, posing the opposite problem of too many elephants. Park management has to make some difficult decisions in the future as to how to balance the growing population with the need to conserve other ecosystem components, including large trees. The CAO has been a vital tool at understanding the patterns of elephant-related treefall, and how they vary throughout the heterogeneous park, providing insights into future directions and implications for elephant management.
CAO scientists have also investigated predator-prey interactions and being among the growing number of studies that challenge long-held views about predator behavior, showing, for example, that male lions actively hunt as females do, but that they use a different strategy in the form of dense vegetation, where human observation is difficult and likely responsible for the long-held view that male lions primarily scavenge their food from females. This finding has great significance for savanna management because it demonstrates that if sustainable predator-prey interactions are to be achieved in protected areas, heterogeneous landscapes will need to be maintained to cater for the hunting behavior of both lion sexes. Other CAO studies have looked at primate behavior in both the Amazon and Panama.
CAO imagery on the left shows lines of sight (white lines) radiating from a lion kill site, indicating the density of vegetation where such kills occur. A male lion in the Kruger National Park (right).
Looking forward, we are expanding our animal ecology research footprint at CAO. We continue to undertake studies in several South African reserves, working with park scientists and management to better understand both the ecosystem-scale impacts and conservation needs of several species. We are also moving beyond Africa and the Americas to incorporate animal ecology studies in upcoming campaigns in Borneo, where an impressive array of species persists within a heavily fragmented and degraded landscape. Much of their resilience relies on the persistence of a few remaining primary forest patches, almost entirely within protected areas. We hope to add to our understanding of how these animals survive in these landscapes and what their habitat needs are for the future, contributing to fundamental ecological science and the sustainable management and conservation of biodiversity.
Contributed by Dr. Andrew Davies, CAO postdoctoral researcher
Asner, G. P., N. Vaughn, I. P. J. Smit, and S. Levick. 2016. Ecosystem-scale effects of megafauna in African savannas. Ecography 39:240-252.
Bakker, E. S., J. L. Gill, C. N. Johnson, F. W. M. Vera, C. J. Sandom, G. P. Asner, and J.-C. Svenning. 2016. Combining paleo-data and modern exclosure experiments to assess the impact of megafauna extinctions on woody vegetation. Proceedings of the National Academy of Sciences 113:847-855.
Davies, A. B. and G. P. Asner. 2014. Advances in animal ecology from 3D-LiDAR ecosystem mapping. Trends in Ecology and Evolution 29:681-691.
Davies, A. B., C. A. Baldeck, and G. P. Asner. 2016. Termite mounds alter the spatial distribution of African savanna tree species. Journal of Biogeography 43:301-313.
Davies, A. B., S. R. Levick, G. P. Asner, M. P. Robertson, B. J. van Rensburg, and C. L. Parr. 2014a. Spatial variability and abiotic determinants of termite mounds throughout a savanna catchment. Ecography 37:852-862.
Davies, A. B., S. R. Levick, M. P. Robertson, B. J. Rensburg, G. P. Asner, and C. L. Parr. 2015. Termite mounds differ in their importance for herbivores across savanna types, seasons and spatial scales. Oikos online early: doi 10.1111/oik.02742.
Davies, A. B., M. P. Robertson, S. R. Levick, G. P. Asner, B. J. van Rensburg, and C. L. Parr. 2014b. Variable effects of termite mounds on African savanna grass communities across a rainfall gradient. Journal of Vegetation Science 25:1405-1416.
Levick, S. R., G. P. Asner, T. Kennedy-Bowdoin, and D. E. Knapp. 2010. The spatial extent of termite influences on herbivore browsing in an African savanna. Biological Conservation 143:2462-2467.
Loarie, S. R., C. J. Tambling, and G. P. Asner. 2013. Lion hunting behaviour and vegetation structure in an African savanna. Animal Behaviour 85:899–906.
Palminteri, S., G. V. N. Powell, G. P. Asner, and C. A. Peres. 2012. LiDAR measurements of canopy structure predict spatial distribution of a tropical mature forest primate. Remote Sensing of Environment 127:98–105.