Population trend
Trend
Although Wild Dogs are crepuscular, they are infrequently seen, and it appears that populations have always existed at low densities compared to other large African carnivores (Creel & Creel 1996). Extreme fluctuations in population size and rapid pack fusion and dissolution, mean that the number of mature individuals alone is often not a good indicator of overall population size and trends. Pack number (the number of potential breeding groups) is therefore thought to be a more robust indicator of population viability, which has increased from an estimated 34 in 2000 to 37 in 2016, chiefly through the roll-out of a managed metapopulation plan (Gusset et al. 2008; Davies-Mostert et al. 2009). Although the increase in breeding groups is small, by January 2016 there were an additional 10 non-breeding groups in managed metapopulation reserves. Given the active management to ensure that dispersers find mates and form breeding groups, the population is likely to be more robust than suggested simply by calculating the number of actively breeding animals (see explanation below).
Estimating the number of mature individuals is challenging, because Wild Dogs are near-obligate cooperative breeders; within a pack, the alpha male and female are the parents of the majority of surviving pups (Girman et al. 1997), although see Spiering et al. (2010) for exceptions. In Wild Dogs, a high proportion of individuals are indeed reproductively suppressed (Creel & Creel 2002), but these animals do not quickly become reproductive if an alpha individual dies, because in southern Africa they are locked into a seasonal reproductive cycle (only breeding once a year; Courchamp & Macdonald 2001). Death of an alpha may therefore lead to the disintegration of the pack, with no breeding until new packs are formed (although this depends on how much time is available before the next breeding season, and can sometimes be countered by direct management). In instances where there are enough unrelated adult males and females (not alphas) to assume dominance, following the death of one or both alpha animals, there is a high probability of pack persistence in the next breeding season.
Mature individuals are defined as those animals considered capable of reproduction within the current breeding season. Two methods were used to determine mature individuals, based on the census data of 37 breeding packs and 382 adults and yearlings in January 2016.
Method 1 (following the 2004 national assessment):
This method assumes that there are, on average, 1.5 adult males and 1.5 adult females per breeding pack. This provides an estimate of 111 mature individuals in 37 breeding packs.
Method 2 (following the 2008 global assessment):
This method allows the estimation of numbers of mature individuals (Nm) from the census population of adults and yearlings (Nc), based on demographic data from large unmanaged populations (Table 2). It assumes that the number of mature individuals thus comprises the sum of the number of alpha males (NaM), alpha females (NaF) and subdominant (that is, non-alpha) animals (Nsub) that breed successfully (Woodroffe & Sillero-Zubiri 2012). It assumes an adult sex ratio of 0.56:0.44 males to females (Table 2).
The number of mature individuals is therefore estimated as:
NaM = Nc x 0.56 x PaM
+ NaF = Nc x 0.44 x PaF
+ Nsub = (NaM x 0.10) + (NaF x 0.08)
where PaM and PaF are the proportion of adults and yearlings that are alpha males and females, respectively (from Table 2). This equation was applied to each segment of the population, providing an estimate of 90 mature individuals (Table 3).
The changes observed over the past three generations can largely be attributed to an increase in the number of reserves participating in the Wild Dog managed metapopulation, which have increased from three in 2000 (Hluhluwe-iMfolozi Park, Madikwe Game Reserve, and Pilanesberg National Park) to 11 in 2016 (Table 4). This increase occurred despite several interim setbacks when Wild Dogs have been removed from some participating reserves. Removals were as a result of perceived impacts on prey populations, and unresolvable conflicts with neighbours due to repeated breakouts (Davies-Mostert et al. 2009). Although the metapopulation network has expanded, and the number of packs and mature individuals has increased slightly, continued work is required to maintain this increase and secure areas large enough to sustain resilient and dynamic packs of Wild Dogs (such as in Kruger).
Populations of Wild Dogs are prone to marked fluctuations at a variety of temporal and geographical scales, which are likely to both increase extinction risks and undermine the precision of population estimates. At the local scale, a combination of high mortality, high fecundity and dispersal by both sexes means that pack size fluctuates substantially over short periods, although fluctuation in numbers of mature individuals would be less dramatic. Because Wild Dogs are seasonal breeders across most of their remaining geographic range, fluctuations may be synchronised across packs. Managed subpopulations in metapopulation reserves are typically small (often only a single pack) and these populations are highly prone to stochastic events, further exacerbating population fluctuations.
The same demographic characteristics â high mortality, high fecundity, and long-distance dispersal â likewise lead to fluctuations at the population scale. This pattern is further exaggerated by the speciesâ susceptibility to infectious diseases which can cause rapid localised die-offs. Massive local declines are not uncommon, and are often both rapid and unanticipated. This is exemplified by the case of Madikwe Game Reserve where, in 1997, a population of 24 animals was reduced to just three individuals following a rabies outbreak in early 1998 (Hofmeyr et al. 2000). During two, more recent incidents, 23 of the 25 Wild Dogs in Khamab Kalahari Reserve (North West) were killed due to a canine distemper virus (CDV) outbreak in 2013, and a rabies outbreak in Madikwe Game Reserve (North West) reduced the population from 30 individuals to just five in December 2015 (WAG-SA minutes).
Similar die-offs have been documented in larger Wild Dog populations. For example, five of 12 study packs in Botswana (Alexander et al. 2010) and three of eight study packs in Kenya (Woodroffe 2011) have been reported as having died within short time periods during disease outbreaks. However, as most Wild Dogs in the metapopulation are regularly vaccinated against rabies and CDV (especially after these catastrophic outbreaks), they are less vulnerable to extinction from disease. Under good conditions, possibly inversely linked to rainfall (see Buettner et al. 2007), or few competing predators (Mills & Gorman 1997), Wild Dog subpopulations are able to grow relatively quickly, and rapid die-offs can be offset naturally by successful reproduction, or by active management, including artificial pack formation and reintroduction.
The Wild Dogâs capacity for very long-range dispersal means that subpopulations sometimes reappear unexpectedly and grow rapidly. Within the assessment region, though, this capacity to seed new subpopulations and grow rapidly is severely compromised by habitat fragmentation, geographic isolation and persecution, which will limit any population recovery. Although Wild Dog populations can exhibit substantial temporal changes, fluctuations in the assessment region have largely been contained by active metapopulation management. Nevertheless, the potential for rapid population fluctuations, combined with severe habitat fragmentation, contribute to their vulnerability to extinction within the region.