Published online by Cambridge University Press: 04 June 2019
On the following morning we were up before the sun, and, travelling in a northerly direction, soon became aware that we were in a district frequented by elephants, for wherever we looked, trees were broken down, large branches snapped off, and bark and leaves strewn about in all directions, whilst the impress of their huge feet was to be seen in every piece of sandy ground. FC Selous (1881, 39), north of Gweru, Zimbabwe, in 1872
THE ISSUE of the effects of elephants within ecosystems has emerged strongly since the formulation of the concept of the ‘elephant problem and the concerns that elephants may irrevocably alter the remaining areas which are available to them’ (Caughley, 1976a). Two perspectives need to be kept in mind when these concerns are raised. Firstly, the order of Proboscideans (including the modern elephants) evolved in Africa as part of a unique group of mammals, the Afrotheria (Robinson & Seiffert, 2003), with their roots going back 80 million years. Proboscideans of various forms subsequently colonised all continents except for Australia and Antarctica; mammoths in the family Elephantidae remained abundant and widespread through most of Europe and North America until as recently as 12 000–16 000 years ago (Sukumar, 2003). The modern African elephant emerged about 3 million years ago. Hence, its relationships with other animal and plant species have been an integral part of the co-evolutionary history of the ecosystems and biodiversity of Africa.
Herbivores, through their consumption of plant tissues, affect the relative growth, survival and reproductive output of these plants, with consequences for vegetation structure, community composition and ecosystem processes (Huntly, 1991). Even relatively small herbivores can have profound effects in shaping ecosystem structure, particularly when they occur at high densities.
For example, Côté et al. (2004), writing about the increase in deer abundance, had the following to say:
They affect the growth and survival of many herb, shrub and tree species, modifying patterns of relative abundance and vegetation dynamics. Cascading effects on other species extend to insects, birds, and other mammals. Sustained over-browsing reduces plant cover and diversity, alters nutrient and carbon cycling, and redirects succession … simplified alternative states appear to be stable and difficult to reverse.