This research project aims to establish the potential impact of climate change on free-ranging aardvarks Orycteropus afer within the Okonjima Nature Reserve. Previous research has shown aardvark to be vulnerable to climate change; in the semi-arid Kalahari aardvarks were recorded as responding to summer droughts in three main physiological ways – switching to diurnal activity patterns, lowering of core body temperatures during metabolically challenging periods and exhibiting basking behaviours. However, such responses were not always successful and resulted in mass mortality of aardvarks following summer droughts. Given the aardvark’s status as an ecosystem engineer a keystone species, due to its burrowing behaviours, the loss of aardvarks from an ecosystem due to climate change is likely to have cascading community impacts.
Climate change on global scale is now occurring at an unprecedented rate. Biodiversity worldwide has already been impacted, and it is predicted that over time many more organisms will be negatively affected. The rise in greenhouse gas emissions due to anthropogenic factors, has led to global temperate rise of approximately 1 o C since 1901, and it is expected to increase at a rate of 0.1 o C per
decade (Jones et al. 2012). Such temperate rises will in turn lead to increases in the number of hot days and nights globally (Alexander 2006) and an increase in the frequency and intensity of extreme weather events such as droughts and floods (Le Roux et al. 2016). Climate change in Africa has been predicted to increase twice as fast as the rest of the world (Niang et al. 2014), and rainfall over Africa has seen a declining trend, and a progressively delayed onset of rains since the mid-20th century (Alexander et al.2016). The southern African sub-region is expected to experience rapid rates of warming, with the strongest effects predicted to occur on the semi-arid south-western parts of Botswana and Namibia and north-western South Africa (Niang et al. 2014).
Aardvark Orycteropus afer, is a solitary, nocturnal, semi-fossorial and myrmecophagus mammal, distributed locally throughout sub-Saharan Africa (Skinner & Smithers 1990). Weighing 40-60 kg, aardvark spend most of their time resting in self-dug burrows from which they emerge from to forage at night. Inhabiting a variety of habitats including open grassland, savannahs, scrubland and thick forests, aardvarks are exposed to a variety of climatic conditions across their range (Lehmann 2009). The species is listed as ‘Least Concern’ by the IUCN Red List, and its distribution is proposed to be determined by the presence of sufficient ant and termite prey populations.
Aardvarks are strictly myrmecophagus; feeding almost exclusively on ants and termites, with several published studies finding ants to dominate the diet throughout the year, with termites being taken mainly in winter. The ants and termites on which aardvark prey live in large underground colonies and aardvark have specialized anatomy which enables them to feed on underground prey. Due to their burrowing activities, aardvarks are considered to be keystone species; impacting their community and ecosystem in a way that is disproportional to their body size (Power et al 1996). Aardvarks are also considered ecosystem engineers as they actively change their environment, by providing valuable microhabitats used by other species (Kinlaw 1999).
The burrows excavated by aardvark provide thermal refuge for a wide variety of species, and their foraging activities expose food sources for commensal feeders and promotes plant germination. Although aardvarks have been recorded as primarily nocturnal (Smithers & Skinner 1990), Taylor and Skinner (2003) recorded aardvarks leaving their burrows during the afternoons in the False Karoo winters. Furthermore, activity ceased during the coldest parts of the night and were never observed above ground at temperatures below 2 o C, which was proposed to be due to their sparse fur cover leaving them susceptible to cold.
Aardvarks are known to have a unique physiology, having a metabolism and body temperature lower than expected for a mammal of their size. Low metabolic rates and body temperature however are typical of myrmecophagus mammals, and have been hypothesised as an adaptation for a semi-fossorial life and a specialisation on a low energy diet of ants and termites (McNab 1984). In a study using internal biologgers in aardvark, Taylor and Skinner (2004) found internal body temperature to range from 34.5 o C to 37.5 o C in summer and from 33.5 o C to 37.5 o C during winter. Body temperatures were lower whilst resting in the burrow and higher when active and foraging, which was hypothesised to be due to the metabolically intensive digging producing body heat.
AARDVARK'S & CLIMATE CHANGE
In a recent study examining the flexibility of aardvark physiology in response to environmental fluctuations, Weyer (2018) found during drought summers in the Kalahari, aardvarks were not able to meet their energetic requirements, which was followed by mass mortality of aardvark at the end of summer, with the few surviving aardvarks showing poor body condition. The energy deficiency was hypothesised due to the droughts causing declines in plant productivity, which in turn resulted in crashes in ant and termite populations. Energy-deficient aardvarks were found to relax the precision of their body regulation, which resulted in a pronounced heterothermy, with low minimum 24-hour body temperatures being recorded, even in high air temperatures. This is in agreement with Rey et al. (2017) who found aardvark minimum 24-hour body temperatures to be lowest during a drought summer in the Kalahari. Body temperature amplitudes of 11.7 o C, and an overall range of 24 – 38 o C were recorded in aardvarks in poor body condition, along with a shift to diurnal activity during drought summers. During drought summers, Weyer (2018) recorded aardvarks shifting their activity by up to 12 hours earlier, becoming entirely diurnal in both the drought summers and winters of drought years, exposing themselves to intense heat which was hypothesised to lead to increased water stress.
Such a complete change in activity patterns of mammals is believed to be an adaptive mechanism which allows nocturnal animals to maintain their energy balance during metabolic challenges; shifting activity from night to day time is believed save up to 10% of a mammals energy output (Van der Vinne et al. 2015). Weyer (2018) believed aardvarks in the Kalahari were employing diurnality to prevent energy losses during high energy needs during cold periods, as well as during periods of low food abundance (i.e. during drought summers), however it was noted that due to the mass mortalities following drought summers, this response to drought was not always successful for aardvark.
During the drought summers in the Kalahari, Weyer (2018) found aardvarks to have remarkably low body temperatures, as low as 25 o C, occurring during foraging in the morning and midday periods. Aardvarks also showed a progressive lowering of body temperatures over several weeks, as their poor nutritional states resulted in them not being able to sustain high body temperatures. When in poor condition, aardvarks were seen to bask outside burrow entrances in winter during the early morning,
which was associated with a rapid, but short term, increase in body temperature. Furthermore, basking was only recorded when body temperatures were lower than normal, indicating they were likely energy deficient. Whilst basking was noted to be a solution to a lower than energy body temperature, Weyer (2018) noted that this behaviour would be associated with a higher predation risk.
AfriCat Aardvark Research
By using VHF tags, aardvarks across Okonjima will be tracked to establish home range sizes, overlap between individuals and burrow locations. Tracking tagged aardvark during the day will allow the active burrow to be locate and a camera trap set-up to record the time of emergence, which will be linked to weather variables to gain a greater insight into the potential impact of climate change on Okonjima’s aardvarks. Additionally, basking behaviours (as previously recorded for poor body condition aardvark) will be monitored with camera traps as will the body score of individual aardvarks, which will show further evidence for the impact of climate change on aardvarks. This will be the first in-depth study on aardvarks for Namibia and will no doubt help us gain a better understanding of these elusive and strange animals.