By Morgan Trimble
As I pushed through thick, towering reeds in the Bangweulu Swamps of northern Zambia, my heart pounded in anticipation of what creature I might find in the clearing beyond. But it was empty. Only a single set of huge, round impressions trailed through the soft mud—the tracks of an elephant that had passed through perhaps a week prior.
I never found their owner. No surprise really. Bangweulu’s few remaining elephants roam the Connecticut-size, 15,000-km2 ecosystem like ghosts. I’d been searching for elephants in one of the most elephant-impoverished parks in Africa.
In a study published today in the scientific journal PLOS ONE, colleagues and I estimate how many savanna elephants Africa’s protected areas would support if not for widespread poaching. The results are sobering. Collectively, these parks are missing 75 percent of their elephants, nearly three-quarters of a million individuals.
We’ve all heard that elephants are in trouble. Now we know just how much.
“It’s Ecology 101,” says Rudi van Aarde, Chair of the Conservation Ecology Research Unit at the University of Pretoria and supervisor of the study. “Resources like food and water limit population size and growth for elephants. Elephants inhabit an incredible array of landscapes, and it’s obvious that a harsh Namibian desert should support a lower density of elephants than, say, a rich, green floodplain along Zambia’s Luangwa river. If left alone, elephant populations will grow to a size dictated by their environment.”
So how many elephants should there be in any given protected area? Researchers have grasped the basic principles for a long time, but science-based estimates remained elusive until now.
As lead author of the study, Ashley Robson, explains, “If you try to relate current elephant density in protected areas across Africa to local vegetation and water availability, you’ll fail. From the colonial era to today, humans have so pervasively affected populations that few if any have grown to a size where resource limitation naturally kicks in to stop growth.”
Our team combed through census data from the past 25 years to find populations that have been relatively stable. We then measured the greenness and wetness of each place with remote sensing technology to quantify the most important resources for elephants.
“We were still missing an important factor,” says Robson, “—poaching. When we added a poaching index to our models, clear relationships emerged, and we had a powerful result. For the first time, we could predict how large savanna elephant populations across the continent would grow, both under the prevailing conditions of today and for a scenario without poaching.”
There are 73 large protected areas across Africa inhabited by savanna elephant populations. They span 21 countries and hold about 240,000 individuals, roughly 50% of the continent’s elephants (including both forest and savanna subspecies). Based on the environmental conditions in each of these parks, we predicted how large their elephant populations would grow if people stopped killing them.
Compared to our predictions, recent elephant census results trigger alarm. In total, 730,000 elephants are missing, and current populations are just a quarter of what they should be. Even worse, one-third of the 73 protected areas are missing >95 percent of their elephants.
“At first, our predictions surprised us,” says Robson. “They seemed high. But then we looked back at the oldest reliable census information from the 1960s and early 70s, before ivory poaching really took off. Places like Selous, Mkomazi, Murchison Falls, Tsavo and the Luangwa Valley had populations remarkably close to our predictions. The conditions we’ve experienced more recently clearly influenced our expectations—this is a case of shifting baselines.”
What are the consequences when an ecosystem loses 95 percent of its elephants? In truth, we don’t know exactly. But without elephants to disperse seeds, open up woodlands, bring leafy canopies to ground level by pushing over trees, and fertilize the savannas with their droppings, other species and ecological processes will suffer.
“Elephants drive savanna dynamics, and their presence creates habitats and opportunities for other species,” says Van Aarde.
We think of protected areas as havens where wildlife thrives without human interference. But when it comes to elephants, protected areas are failing. If elephant populations are so massively reduced even where protected, what about populations in the 70 percent of elephant range beyond park boundaries?
Still, this study has an element of good news.
Robson says, “For the first time ever, we have positive conservation targets. We no longer need to measure conservation success solely against the zero-point of extinction or in comparison to the previous years’ counts. Instead, we can aim for these ecologically relevant benchmarks. We can direct funding and effort where it’s needed most.”
Robson, Van Aarde, and I collaborated on this study with Andrew Purdon (University of Pretoria), Kim Young-Overton (Panthera), and Stuart Pimm (Doris Duke Professor of Conservation Ecology, Duke Nicholas School of the Environment). The International Fund for Animal Welfare, the National Research Foundation, and University of Pretoria funded the study.
Citation: “Savanna elephant numbers are only a quarter of their expected values,” Ashley S Robson, Morgan J Trimble, Andrew Purdon, Kim D Young-Overton, Stuart L Pimm, Rudi J van Aarde. PLOS ONE; April 17, 2017.
Dr. Morgan Trimble is an ecologist, writer, and photographer. The author’s opinions are her own and not necessarily those of her co-authors or their organizations.