Elbows deep in ellie research
HOW DO you count small, soft honeydew melon seeds in steaming piles of elephant dung? Just ask Katherine Gordon.
But rummaging through the 100kg of dung a male elephant produces a night, she says, is “quite hard work”.
Her pioneering research, together with colleagues UCT Professor William Bond of the SA Environmental Observation Network and Michelle Henley, of Elephants Alive, has uncovered how the African pachyderms can transport seeds as far as 65km – farther than any other land animal.
Gordon spent a week feeding the fruit to two males and two female elephants at the Elephant Whisperers elephant sanctuary near the Kruger National Park.
“We recorded the time that the melon seeds were passed to generate what is called a ‘gut passage curve’,” she explains.
“We then combined this data with eight years of elephant movement data collected from 38 collared wild elephants in the Kruger, to estimate the spatial scale over which they disperse these seeds.
“They appear to disperse seeds further than every other terrestrial vertebrate disperser yet investigated. In addition, they disperse seeds in an order of magnitude greater than the distances achieved by Asian forest elephants (6km in maximum gut passage time).”
Their paper, Seed dispersal kernel of the largest surviving megaherbivore – the African savanna elephant, published in the journal Biotropica, provides the first detailed account of the spatial scale at which African savanna elephants disperse seeds.
“These findings suggest the savanna elephant is the longest distance terrestrial vertebrate disperser yet investigated,” says Gordon. “Our mechanistic model predicts that 50% of seeds are carried over 2.5km, and distances up to 65km are achievable in maximum gut passage time.
“Maintaining their ecological role as a seed disperser may be a significant factor in the conservation of large-fruited tree diversity within the savannas.”
The idea grew while she worked as a field assistant on a chimpanzee and gorilla study in the Cameroonian lowland forests.
“We followed groups of gorillas and chimps for the duration of each day and made observational notes in addition to collecting their faeces to quantify how many seeds from how many different plant species they were responsible for dispersing.”
Then, while doing her honours at UCT, she became captivated by an ecology course by Bond. “On meeting, William suggested that using the data I had collected we could explore how far chimps and gorillas were moving seeds. Moving on to our local savanna megaherbivores was a natural progression.”
The African savanna elephant, the largest remaining megaherbivore, offers valuable insights into the seed dispersal services provided by extinct megafauna in prehistoric times, say the authors.
This research highlights the important role of megaherbivores, animals that weigh over 1 000kg, in the dispersal of large savanna seeds.
But climate change presents uncertainties. “Biomes will need to move in response to a changing climate.
“If the seeds are not present in the seed banks of surrounding areas, the biomes will not be able to shift. Megaherbivores might have a very important role in moving seeds to new seed banks.”
Elephant killings, too – on the rise in the Kruger – could affect seed dispersal. “The loss of elephants will likely have very negative consequences for those species that are highly reliant on elephants for their effective dispersal,” Gordon says.
“A few examples of savanna tree species are the marula, baobab and the manketti. We’re exploring the consequences of the loss of elephants to these species and to a number of others.”
Bond says: “Kath’s study showed elephants can move a seed up to 60km or so! That is pretty amazing.”