Professor Rudi van Aarde directs the Conservation Ecology Research Unit (CERU) as a self-sufficient research entity in the Department of Zoology and Entomology at the University of Pretoria. His research focuses on the conservation management of savanna elephants and on the ecological restoration of coastal forests. He is the author or co-author of 195 peer-reviewed scientific papers, 13 book chapters, 126 technical reports, 56 popular articles, and has presented his research findings on 111 occasions at national or international conferences and public forums, several of these as invited speaker or guest lecturer. He has supervised 67 PhD and MSc students since 1991, as well as 11 post-doctoral fellows. He is an active member of the Royal Society of South Africa (RSSAf); the Zoological Society of southern Africa (ZSSA); the Southern African Wildlife Management Association (SAWMA); the Society for Restoration Ecology (SRE); and the Society for Conservation Biology (SCB). He has been a council member of ZSSA and SAWMA, president of SAWMA, and has served on several conservation management committees. He regularly reviews papers for high impact factor scientific journals in his field of specialisation, including Journal of Animal Ecology, Biological Conservation, Journal of Biogeography, Journal of Animal Conservation, Restoration Ecology, and the Journal of Applied Ecology, and serves on international research grant and evaluation committees. He frequently advises industry, government and conservation departments on conservation-related issues. The University of Pretoria has awarded him for exceptional academic achievement on four occasions, and he is a Fellow of the RSSAf.
Van Aarde established CERU in 1998. His chair is self-funded via grants from national and international organisations and private industries. These grants, as well as contracts, provide for the employment of research fellows, support staff and post-graduate bursaries. Collaborative research with Professor Stuart Pimm (Doris Duke Professor at Duke University, USA) strengthens CERU’s academic activity. Van Aarde is widely recognised for his research on the response of elephants to environmental gradients, and for applying ecologically-sound principles to the rehabilitation of coastal dune forest.
His research on elephants is conducted across gradients of environmental and management conditions in protected areas across Mozambique, Malawi, Zambia, Botswana, Namibia and South Africa. His development of the ‘megaparks for metapopulations’ concept is an innovative platform for elephant management and places emphasis on the spatial structuring of populations and their demographic responses to structural heterogeneity in environmental resources. This management is employed in several southern African countries and has important implications for the conservation of several mega-herbivores. Through his publications and invited participation in the science round-table that assessed elephant management in South Africa during 2007, he played a pivotal role in extending management options for elephants.
Van Aarde’s research on the restoration of coastal dune forest in northern KwaZulu-Natal (South Africa) started 25 years ago. The work is supported by industry, the NRF and THRIP. Coastal dune forest is rare in South Africa and falls within the Maputaland-Pondoland-Albany biodiversity hotspot. Some 10% of this forest is protected, but 43% has been transformed. The remaining 57% is threatened by tourism, dune mining and clearing for subsistence living. The narrow and linear natures of the forest further contribute to its sensitivity to transformation, isolation and fragmentation, and its restoration makes both conservation and economic sense. The project is now well established and van Aarde’s scientific achievements here provide a recognised scientific foundation for restoration ecology in southern Africa.
Brief description of completed research (2008 – 2017)
The spatial dynamics of southern Africa’s elephant populations
My research from 2008-2017 focussed on addressing the following questions. How many elephants should there be? What do elephants do to other species? What can we do for elephants? These revolve on the demographic and spatial responses of elephant populations to different environmental and management conditions as well as to the restoration of the spatial structuring of populations to reinstate metadynamics. Barriers and management actions that limit elephant dispersal, artificial water supplies that alter survival, and a spatial configuration of protected areas that hinders seasonal spatial use, may cause demographic anomalies that might explain perceived ‘elephant problems’. My research provides solutions to these problems.
Based on the analyses of 73 independent time series we have identified 18 stable populations and characterised through modelling environmental parameters (EVI and distance from water) and social variables (poaching levels) that alter asymptotic levels Robson et al. (2017). Our model predicted asymptotes for non-stable populations and showed a 75% deficit in the 73 populations that collectively represent half of Africa’s savanna elephants. We thus now have an ecologically derived and novel estimate of the number of elephants that should occur in most of southern Africa’s protected areas and can inform conservation incentives to attain such levels. Our studies on the consequences of stability for other species and on the responses of age specific survival and reproduction to resource limitations that impose stability are still at an early stage but already have produced publishable results (i.e. Trimble et al. 2009; Shrader et al. 2010; Young & van Aarde 2010).
A recent update of elephant impact (Guldemond et al. in review) suggest that few studies meet criteria to be included in a proper meta-analysis, and that two thirds of those that do so suggest negative impacts that could not be assigned to elephant densities or management histories. Across Africa, impact is not a function of density, but difficult to assess because only a quarter of studies conducted since 1985 provide data for inclusion in our recent meta-analyses (Guldemond et al. in review). Lack of impact may be due to density dependent resource selection with selection decreasing with increasing density and in response to the distribution of artificial watering points (Purdon & van Aarde 2017). Birth rates varied little from year to year but survival of calves responded negatively to low rainfall (Robson 2016) and high densities, which induces changes in roaming behaviour and which reduces calve survival (Young & van Aarde 2010). Heat spells typical of much of the distributional range of elephants might explain calf mortalities as a cost induced by adaptive behavioural plasticity that limits foraging opportunities (Mole et al. 2016). These findings have important management implications (see Young & van Aarde 2011).
We built demographic profiles for 22 populations after designing a method to age elephants from body measures (Shrader et al. 2006a & 2006b; Trimble et al. 2011) and after evaluating and developing methods to quantify age at first breeding, length of calving intervals, and age-specific survival rates (Ferreira & van Aarde 2008). We related differences in fecundity and survival of 17 populations to rainfall and integrated normalized difference vegetation index (INDVI). For 12 of these populations, INDVI during conception and gestation best explained anomalous age structures. In dry savannas juvenile survival drove such anomalies (Trimble et al. 2009).
Elephants born in high rainfall years survived better than those born in low rainfall years, but the relationship was weak, except for fenced populations with access to artificial water, where rainfall greatly influenced juvenile survival. Food restrictions during droughts therefore reduced calf survival and we suggest that damage to vegetation can be prevented by reducing water sources and removing fences (Shrader et al. 2010). Satellite tracking of 73 breeding herds at 13 locations showed that certain management interventions reduced seasonal variation in ranging patterns and increased local impacts on vegetation. Artificial water sources allowed more extensive dry season ranging and enabled elephants to use vegetation in areas that would otherwise have been inaccessible (Purdon & van Aarde 2017). Fences also caused elephants to ‘‘bunch-up” against them during the wet season, again increasing their pressure on resources (Loarie et al. 2009).
Food availability during the wet season, and heterogeneity in its distribution during the dry season explained home range variability across southern Africa (Young et al. 2009a; Purdon 2016). However, as densities increased this relationship weakened and less preferred habitats were then occupied (Young et al. 2009b; Robson 2016). Across 13 protected areas, dry season daily roaming distances increased with densities and this reduced the survival of weaned calves. This analysis enabled the first quantification of behaviourally-mediated density dependence, but fences and artificial water negated dependence (Young & van Aarde 2010). Artificial water supplies drove vegetation impact by altering range use (Grainger et al. 2005; van Aarde et al. 2006; de Beer et al. 2006; de Beer & van Aarde 2008; Purdon 2016) and dictating habitat selection (Harris et al. 2008; Robson 2016).
Outside protected areas the spatial overlap between people and elephants causes conflict (Jackson et al. 2008; Roever et al. 2014). Range limitations can be addressed by linking protected areas in order to restore seasonal and regional land use patterns (van Aarde et al. 2006; Roever et al. 2013). We advocate scientifically-based management that relies on networks of national and trans-boundary megaparks to restore spatial dynamics (van Aarde & Jackson 2007). Implicit in this solution is the dispersal-associated stabilization in density, which we demonstrated for Africa’s largest elephant population (Junker et al. 2008), whereas anomalous growth rates were typical for populations deprived of dispersal opportunities (van Aarde et al. 2008; Robson 2016). Our literature review (Olivier et al. 2009) provided impetus for the application of metapopulation management but managers tend to rely on experience rather than scientific evidence (Young & van Aarde 2011). Our approach now requires implementation and SANPark’s moratorium on culling, reduced water supplies and increased ranges for elephants provide for the advocated spatial structuring of populations. Our focus on the development of sub-continental scale conservation management options for elephants may also benefit other species, and have positive spinoffs in socio-economic and political arenas.
Based on the satellite tracking of 26 breeding herds for three consecutive years in Kruger National Park we established that artificial waterholes allowed elephants to use areas more than double the distance away from rivers, increasing the total area they used in Kruger by more than a third. Additionally, artificial waterholes increased the intensity of use in some areas. Water provisioning in Kruger alters elephant spatial utilisation patterns. Closing down these artificial waterholes might create a desirable outcome for conservation management centred on promoting ecological processes that may limit elephant numbers and their impact on vegetation (Purdon & van Aarde 2017).
Elephants occur in fragmented and isolated populations across southern Africa. Transfrontier conservation efforts aim at preventing the negative effects of population fragmentation by maintaining and restoring linkages between protected areas. We recently identified possible genetic linkages by comparing the genetic characteristic of elephants in Kruger National Park (South Africa) to populations in national parks in nearby countries (Botswana, Mozambique, Zambia and Zimbabwe. The mtDNA and nDNA population structure were incongruent, likely reflecting female philopatry and male-mediated dispersal. High genetic diversity among elephants in Kruger, and shared mtDNA haplotypes with parks north and south of Kruger suggest that this population was established by multiple founder populations and/or the original genetic diversity of the founder population has since been augmented through gene flow and immigrations from proximate parks (de Flamingh et al. in review). Our findings highlight the need for conservation initiatives that aim at maintaining connectivity between populations. Such initiatives may provide a sustainable, self-regulating management approach for elephants in southern Africa while simultaneously upholding/maintaining genetic diversity and gene flow within and between protected areas as we have illustrated for northern Botswana (de Flamingh et al. 2014).
Our efforts to answer three simple questions relevant to elephant conservation yielded exciting and original opportunities, proved to be productive and have yielded new opportunities of finding solutions.
Ecological restoration of coastal dune forests in KwaZulu-Natal
Research started in 1992 and for the last eight years emphasized ecological processes that may strengthen or derail forest restoration after strip mining activities. Thirty-eight years of post-mining restoration generated this outdoor research laboratory where the initial reshaping and stabilization of dunes provides for the regeneration of forests through natural processes (van Aarde et al. 1996; Wassenaar et al. 2005; Rolo et al. 2016). Our peer-reviewed science provides rigour for the evaluation of the restoration as a conservation initiative and for pro-active management (Wassenaar et al. 2008; Rolo et al. 2016).
We used our empirical data to verify expected succession, and to determine some of the local and regional drivers of colonisation processes (Olivier & van Aarde 2014; Rolo et al. 2016). We expect age-related regeneration to give rise to increased complexity and heterogeneity as forest communities re-assemble through the addition and replacement of species which may be limited by niche properties and regional events. Furthermore, regeneration should induce convergence towards bench-mark target values in assembly properties. To assess these we continued to survey community properties at various trophic levels along a succesional sere. We now have near annual data for a 20-year period on the compositional, structural and functional properties of seral stages of forest regeneration, as well as several old growth forest fragments that serve as benchmarks.
Regeneration trajectories for soil properties, herb, tree, dung beetle, millipede, bird, and mammal assemblages show that rehabilitation enables convergence in community properties within a reasonable period, but idiosyncratic trends vary from one trophic level to another (Wassenaar et al. 2005; Grainger et al. 2011; Rolo et al. 2016). Few assemblages converge exponentially and trends vary with indices. Consequently, the acceptance of convergence depends on what one measures (Wassenaar et al. 2005). Variability in composition and structure may be natural, unless induced by site-specific anomalies that could jeopardize restoration. We developed a technique to flag aberrations (Wassenaar et al. 2007) and this allows management to wisely use scarce resources to mitigate aberrations and improve restoration success. Our technique uses a permutation test to identify variables that vary more than expected. Consequently, we identified colonization constraints due to distance and isolation effects. Contrary to our expectations, patch age only explained the patch occupancy of a third of bird species and half of the woody plant species. Landscape parameters that measure edge, isolation, and area explained patch occupancy for most birds and half of the plant species. Varied responses are constrained by habitat and dispersal, but we cannot ignore regional limitations (Grainger et al. 2011). For instance, for birds Trimble & van Aarde (2011) illustrated that three quarters of bird populations in our study area declined at about 12% per year over a period of 13 years – this implies that bird numbers halved every five years. Below average rainfall may have contributed to declines, but species with larger ranges tended to decline more sharply than did others. Declines may thus be due to environmental changes at a broader geographical scale. These trends have undesirable consequences for restoration.
Taxon specific regeneration responses differed among taxa. For instance, dung beetles responded to micro-climatic conditions rather than the age of rehabilitating sites (Davies et al. 2003). Colonisation of regenerating forests by millipedes, on the other hand, is by distance to potential source areas (Redi et al. 2005) but induces successional patterns. Soil micro-arthropod communities are re-assembling at much slower rates than all other taxa (Kumssa et al. 2004). Edge effects of roads altered community composition and structure in different ways for millipedes, birds and rodents (Weiermans & van Aarde 2003) and may impair forest restoration. Edges along roads favour exotic invaders but these herbs assembled at rates similar to those of indigenous species and had no discernible effects on non-native plant species (Grainger & van Aarde 2011). Moreover, at the local scale, Grainger & van Aarde (2012) show that pioneer tree biomass and their replacement forest canopy trees support succession as the principle driver of early restoration.
We further validated that succession is the principle driver of regenerating trajectories by comparing predicted values of tree communities attributes to observed values over time. Our results indicate that changes in forest structure and function can be predicted using a space-for-time substitution approach (Rolo et al 2016). The sharply decrease in tree pioneer species at early regenerating stages predicted by a chronsequence was corroborated when surveying the same sites over time. Similarly, we observed that the functional diversity of regenerating forest developed in a predictable fashion and in accordance with the successional models of vegetation development (Rolo et al 2016). We observed that functional trait space, based on regenerating attributes, increased linearly over time. Indicating that tree communities at late regenerating stages are more functionally different than expected by chance. These results corroborate that the assemblage of tree species into communities is more likely to be driven by niche rather than by neutral processes. However, the functional trait space based on reproductive traits may be more linked to processes operating at the landscape scale than to local processes. Indeed, when assessing the functional trait space of regenerating forest based on functional traits that depend on local biotic and abiotic conditions, we observed the opposite pattern, showing a significant decrease over time.
At the regional scale, we developed a model to predict where coastal forests should occur in the absence of anthropogenic disturbances. Our model suggests that 82% of coastal forests in KwaZulu-Natal may have been lost and that the remaining forests now harbour an extinction debt of 14 bird species (Olivier et al. 2013). This highlights the importance of restoration efforts to regain some of the forest habitat that has been lost. To direct restoration efforts at the landscape scale, we developed a spatial model to identify which forest fragments in the region are degenerating and/or regenerating (Olivier et al. 2017). By restoring forest across the landscape, we not only increase forest habitat area, but also increase connectivity among remaining fragments. Our research on similar and other forests in southern Mozambique highlights the importance of connectedness between naturally fragmented forests (Guldemond & van Aarde 2010; Olivier & van Aarde 2014; Freeman in review). For instance, when human land-use types surround coastal forest fragments, forest specialist bird species disappear from these fragments (Freeman in review). This likely happens because human land-use types restrict the movements of fragment-dwelling species, but also because these habitats degrade the coastal forest tree community. Moreover, more connected habitats harbour more species of insectivorous bird species (Olivier & van Aarde 2016). Maximising fragment connectivity, but also protecting the tree community within fragments from degradation therefore seems to be an effective strategy to conserve coastal forest species.