Epsilon Archive for Student Projects

Abstract

African megaherbivores are ecosystem engineers, which are under threat of extinction caused by, among others, poaching and climate change. Their current rates of loss means that there’s a need to better analyse their impact on the environment, in order to predict the consequences of losing this group. One of the ways herbivores are influencing their habitat is by defecating in a certain spot, altering the nitrogen to phosphorus (N:P) ratio of the soil and therefore changing the nutrient availability to different plant species, which could change the structure and/or the composition of the vegetation. Therefore, the main objective of this thesis is to determine how body mass, feeding strategy and digestive type of various mammalian herbivores influences the spatial distribution of dung, nitrogen and phosphorus. I focused on two aspects in which species influence nutrient dynamics differently: (1) the variation among species in terms of dung nutrient content and (2) the way species differ in distributing dung and thus overall faecal nutrients.

From January to April 2018 I collected dung from all abundant mammalian herbivore species in Hluhluwe-Imfolozi Park (HiP). The nitrogen and phosphorus concentration in the dung samples were determined. I found that the N:P ratio in dung increases with body mass as a result of a decrease in the concentration of phosphorus. The N:P ratio in browser and mixed-feeder dung is significantly higher than the ratio in grazer dung, driven by higher concentrations of nitrogen in browser dung versus grazer dung. Also, the results showed that, even though the average N:P ratio in dung of ruminants and non-ruminants did not differ significantly, the concentration of nitrogen and phosphorus were significantly higher in ruminant dung.

In order to find the pattern of dung distribution through HiP, I combined my qualitative data with quantitative data from a long term study where herbivore dung was counted along 24 line transects. The impact of herbivores on the distribution of nitrogen and phosphorus is found to be highly complex. Differences between species in body mass, feeding strategy and digestive type all contribute to the concentrations of nitrogen and phosphorus in dung and therefore the distribution of these nutrients over an area. This leads to the conclusion that the effect of megaherbivore extinction will differ per area depending on the identity of the megaherbivores living in that area. Possible consequences for nature reserves are changes in abundance of smaller herbivore and vegetation structures.

In HiP the expected result of megaherbivore extinction, when looking at the nutrient distribution, will be a decrease in the amount of phosphorus distributed through herbivore dung. The nitrogen distribution through herbivore dung is expected to show minimal change.

The composition of the African herbivore community is changing and to predict the full consequences of these changes it is important to conduct additional research which combines the effects of herbivory with studies on nutrient distribution.