Local Extinction of African Wild Dogs in The Serengeti National Park

Transcription

1 Katie Holmes Sophomore College 2017 Local Extinction of African Wild Dogs in The Serengeti National Park Contents I. Abstract II. Introduction III. Methods IV. Background on African Wild Dogs V. Hypotheses VI. Findings VII. Conclusion Abstract African Wild Dogs are currently listed as an endangered species with the International Union for Conservation of Nature (IUCN). Today, only 6,600 remain and some populations have been wiped out entirely (Woodroffe et al 2012: 6). In the 1990s, this was the case for the population of wild dogs living in the Serengeti National Park in northern Tanzania. During this time, the population dwindled to the point of a local extinction. This paper investigates the major factors (causes that contributed most to the decline) that led to this local extinction with a specific focus on predation, interspecific competition, and rabies. 1

2 Introduction The African Wild Dog population has been rapidly declining for several decades. The population is threatened by climate change, interspecific competition, infectious disease, fragmented habitat, poisoning, shooting, and snaring (Creel & Creel 2002). Historically, the animals were thought to be brutal killers and dangerous to humans (neither of which is entirely accurate). Unfortunately, this negative perception has had dire consequences for the species. For example, over a 19-year period starting in 1956, more than 3,400 wild dogs were shot in Zimbabwe. In the decade following, hundreds were shot in a game reserve in Tanzania (Creel and Creel 2002: 8). In the 1980s, measures were taken to protect the population including legal protection in six countries: Botswana, Kenya, South Africa, Tanzania, Zambia, Zimbabwe. Unfortunately, the population did not recover even under new protection and was declared endangered in 2008 (Woodroffe et al 2012, 6). But, the trend has not stopped. Since the late 1990s, the population has decreased by more than 17%. Today, less than 6,600 animals remain, only 1,400 of which are mature adults (Woodroffe et al 2012, 6). To conserve this species, we must understand the reasons for its rapid decline. The Wild Dog population in the Serengeti National Park suffered a tremendous decline to the point of a local extinction. The population was low to begin with 2

3 at the time researchers began studying the population in the 1960s (less than 80 individuals), but by 1992, all the individuals had died or disappeared (figure 1) (Ginsberg et al. 1995: 223). To learn more, I posed the question: what were the main factors that led to the local extinction of the African Wild Dogs in the Serengeti National Park in the early 1990s? Methods To explore my research question, I read peer-reviewed papers from the 1990s to 2010s as well as articles from well-known media outlets. I also spoke with Tanzanians in-country to glean knowledge from local insight. Background on African Wild Dog Physical Features African Wild Dogs are known for their big ears and unique coloring. In fact, every animal has its own pattern. Pups are born black and white and then acquire the tan coloring as they age. Wild dogs are medium-sized, so they are slightly over 2 feet tall and weighing between 45 and 55 pounds (National Geographic 1999). Many people hear dog and assume that means wild dogs are closely related to domestic dogs. In fact, that is not the case. A wild dog, with its anatomy and behavior, is actually most similar to a wolf (National Geographic 1999). Understanding the specific behavior of this species is important to understanding the potential threats it may be experiencing. 3

4 Life in a Pack Wild dogs live in packs of generally about 10 individuals, but sometimes those packs get as big as 20 or 30 animals. In each pack, there is one alpha male and one alpha female. These two are the only pair that mate. A female generally has a litter of about 10 pups (the equivalent of an entire pack). The rest of the pack supports the alpha male and female in the raising of the pups (National Geographic) If more females were to give birth, there would be too many pups to look after. Wild dogs work together as a team in many ways. In the Serengeti National Park, their main prey is the Thomson's Gazelle (but their diet also includes Wildebeest calves during calving season) (Burrows 1994: 285). Wild dogs are generally not as fast as their prey, but have high endurance and work well in teams. African Wild Dogs are an important predator in the Serengeti. Especially with their specific focus on Thomson s Gazelle, wild dogs have a niche role that keeps other populations in check. Recent Discoveries in Interesting Behavior In recent news, media outlets like NPR and CNN shared a story in which they showed that wild dogs sneeze to make group decisions. When a wild dog thinks it s time to hunt he/she will sneeze. Others, if they agree, will sneeze as well. The pack has reached a consensus when all 4

5 members have sneezed (NPR 2017). Not only does this species play a key role in the ecosystem, but it can tell us a lot about a very unique form of group-decision making. Hypotheses For this research project, I had two hypotheses. 1. Increased predation and competition were majors causes of the wild dog decline in the Serengeti National Park. 2. An outbreak of rabies that spread from directly from domestic dogs was a major cause in the wild dog decline in the Serengeti National Park. Findings Increased Predation and Competition Hypothesis 1: Increased predation and competition were major causes in the decline of the wild dogs in the Serengeti National Park. 5

6 When looking at the population sizes for prey species of the African Wild Dog, the numbers suggest that prey was not lacking. In fact, during the period of the wild dog decline, the wildebeest population went up 400% and the Thomson's Gazelle population went up 150% (Ginsberg et al. 1995: 225) It is evident that African Wild Dogs were not suffering from limited prey availability. So if wildebeest and Thomson's Gazelle numbers were increasing, what did the competitor populations look like? It appears that they were increasing as well. The same study showed that hyena populations went up 150% and lion populations also increased dramatically (Ginsberg et al. 1995: 226). What effect might this have had on a wild dog population? In a 1997 study by Creel and Creel, lion populations in five protected areas were measured against wild dog populations. The trend among the data showed a negative correlation between the two population sizes (see figure 2). In other words, with more lions, there were fewer wild dogs and vice versa. This makes sense because lions are wild dogs main predators (National Geographic 1999). 6

7 With less predation, the wild dogs have a higher chance of survival. In the same study, the researchers found that hyena populations numbers have the same correlation with wild dog population numbers as lion populations do. In the same five protected areas, there is a similar trend line in that with more hyenas, there tends to be less wild dogs (figure 3). This is the case because hyenas steal kills from the wild dogs. In a study from 1985 to 1987, hyenas were present at 86% of wild dog kills and ate at 100% of them (Creel & Creel 1997: 4). This can have dire effects on a pack of wild dogs who cannot feed themselves. Hyenas are bigger and far more intimidating, especially when hunting in numbers. During the time of the decline, hyenas immensely outnumbered the wild dogs in the Serengeti National Park. In fact, it s estimated that there were more hyenas in the Serengeti than wild dogs in all of 7

8 Africa (Creel and Creel 1997: 4) Strong evidence exists in support of the hypothesis that increased predation and competition were factors in the decline of the Wild Dogs in the Serengeti National Park. Hypothesis 1 Increased predation and competition were major reasons for the decline of the wild dogs in the Serengeti National Park. Supported. Rabies in the Wild Dog Population Hypothesis 2: An outbreak of rabies that spread directly from domestic dogs to African Wild Dogs was a major cause of the decline of the Wild Dogs in the Serengeti National Park. When researchers started going into the Serengeti to observe populations in the 60s they began to see symptoms that resemble rabies symptoms such as weakness, incoordination, hind-limb paralysis, and discharge from the eyes in the population (Kat et al. 1995: 1) Then, in the Masai Mara, a protected area in Kenya that borders the northern boundary of the Serengeti, a pack was confirmed to have rabies. In just 44 days, 21 of the 23 individuals died from symptoms typical of rabies. Of the 21 deaths, 4 were confirmed to be rabies through laboratory testing (Kat et al. 1995: 1). When it became clear that the region was perhaps under threat of rabies, researchers actively looked for symptoms from the wild dogs in the Serengeti. 8

9 In August 1990, a wild dog was found dead. Next to the adult male was a living male and six pups. All the living animals were thin, restless, and generally acting out of the ordinary. The pups were even eating the carcass, a behavior that would not common within a healthy pack. A GPS-collar was placed on the living adult male. The next day, the pups could not be found, but the adult male was found 10 kilometers away. His behavior was even more bizarre and included lying out in the hot sun alone, chewing skulls, and suffering from hind limb ataxia (impaired coordination). Unfortunately, that dog was lost overnight (researchers believe he died underground) (Gascoyne et al. 1993: 397). These symptoms were terrible and unfortunately, not uncommon. At the same time, brain stem samples were collected from the dead wild dog. Those samples were sent to France to be tested in a lab. Rabies were confirmed both through direct immunofluorescence (direct testing) and mouse inoculation (Gascoyne et al. 1993: 396) This is evidence that rabies impacted individuals in that particular pack, but what do we know about the other remaining packs at the time? Well, between 1986 and 1991, fifteen packs remained. Of the fifteen, eight packs disappeared unobserved, two packs disappeared following undiagnosed signs of rabies, and fives packs had diagnosed rabies (Cleaveland 2007: 613). This means that up to half the population was affected by the disease. This may even be a low estimate considering the other half that disappeared unobserved could have had rabies as well. Rabies definitely took a toll on the remaining wild dog population in the Serengeti. 9

10 Source of the Rabies The next part of hypothesis two involves the source of the rabies. To this day, the source of the rabies is still not entirely clear. Many believe that the wild dogs were the direct source of the disease. There is evidence to support this. For one, 80% of confirmed Tanzanian rabies cases at the time were reported in domestic dogs (Gascoyne 1993: 418). Also, there were approximately 30,000 dogs living within 20 kilometers of the Serengeti Park boundaries (Cleaveland 2006: 618). While it's unlikely that Tanzanians were frequently reporting rabies cases in non-domestic animals living outside the community, there is something to be said for the large numbers of domestic dogs carrying the virus. Further, the virus found in the African Wild Dog was was indistinguishable from the virus isolated from a domestic dog in an area adjacent to the Serengeti National Park. (Gascoyne 1993: 416) This similarity in viral make-up made researchers wonder if the disease was contracted from domestic dogs. It is clear that both domestic dogs and African Wild dogs were exposed to the virus, but can we conclude one species directly gave it to the other? To support this, evidence of direct contact is necessary. During the time of the population collapse, there was no empirical evidence to suggest that the two groups of animals did in fact interact. To learn more about the likelihood that they did come into contact, I looked at more studies of the population in the region today. 10

11 One of those studies explored the large home ranges of African Wild Dogs. This 2012 study tracked two different packs as they moved through the Serengeti-Mara Ecosystem. One pack was tracked for 120 days and traveled 1642 kilometers. The other pack was tracked for 261 days, and traveled 3892 kilometers (Masenga et al. 2012: 2). Those routes were mapped and both packs traveled through areas of human settlement (figure 4). With the wild dogs extensive home range movement, it s likely that wild dogs from the Serengeti moved through communities, possibly coming into contact with domestic dogs. Another recent study explored the contact rate between wild and domestic dogs, again hoping to shine light on the reason for the local extinction in the Serengeti. This study, conducted from 2004 to 2005 took place in the Laikipia, Samburu, and Isiolo districts of Kenya. To investigate transmission risk, GPS collars were placed on 21 domestic dogs and individuals in 15 wild dog packs. This study mapped patterns of movement from all individuals to see how often these animals came into contact. The results did not support the hypothesis suggesting domestic dogs were directly transmitting rabies. In the 183 days that the study took place, wild dogs and 11

12 domestic dogs were never found less than 500 meters apart (Woodroffe et al. 2011: 1349). This means that for the duration of the study (approximately six months), there was a contact rate of zero between the species. Domestic dogs were far more likely to stay near bomas (Maasai communities) and the opposite was true for wild dogs (see figure 5) (Woodroffe et al. 2011: 1349). This transmission rate does not support hypothesis two. If not directly transmitted from domestic dogs, what other species could have been transmitters? There were several other animals with rabies at the time. Lions, jackals, Bat-eared foxes, and Spotted hyenas all suffered from the virus. The Bat-eared fox population especially suffered during this period; one study showed that 60% of the adult female population and 20% of the adult male and cub population died from rabies (Cleveland 2007: 631). As mentioned earlier, Spotted hyenas were found at most of the wild dog kills in the Serengeti. It s possible that rabies could have been transmitted during these encounters. Wild dogs are vulnerable to this type of transmission (called spillover transmission) from more abundant carnivores, particularly where interspecific competition is intense (Creel and Creel 1997: 13). It should be mentioned that domestic dogs could have transmitted rabies to these other animals, although that is unclear at this point to. Through this research, we can 12

13 partially support hypothesis two; we do know that rabies were a factor in the decline of the wild dogs in the Serengeti National Park, but the direct source may not have been domestic dogs (although it could have been an indirect source). With knowledge that other animals were rabies-positive and with limited evidence of transmission rates, more evidence is needed to support that part of the hypothesis. Hypothesis 2 An outbreak of rabies that spread from directly from domestic dogs was a major cause of the decline of the wild dogs in the Serengeti National Park. Partially supported, partially inconclusive. Conclusion Wild Dogs in the Serengeti Today In the 1990s, researchers vaccinated two of the remaining packs in the Serengeti. While vaccinating wild animals is still controversial, this round of vaccinations seemed to have been successful. Recently, kin of those packs were found outside of the Serengeti National Park. Those packs (and a few others) have now be relocated back into the park through the Serengeti Wild Dog Conservation Project (singita.org). So far, the relocated Wild Dogs seem to be doing okay! Finding Meaning from the Research From this research, there is evidence to support that the Serengeti Wild Dog population was affected by interspecific competition, predation, and an outbreak of rabies (for which we do not know the direct source of transmission). While this research is certainly revealing of threats 13

14 to wild dogs, we must be cautious with how we apply the findings. This specific population was affected by these threats, but that does not mean that all populations are. Further, it is likely that the population plummeted because multiple factors were at play. In a simulation run by Vucetich and Creel in 1999, the probability that a population of 98 wild dogs would last 50 years during an outbreak of rabies was plotted. The independent variable was lion density. With a high lion density, the estimated chance of population survival was considerably lower than with a moderate lion density (figure 6) (Vucetich & Creel 1999: 1177). Creel and Creel put it well: while it is clear that infectious diseases can deliver a knockout punch to a population such as the one in the Serengeti National Park (SNP), it may be misleading to generalize conclusions from SNP about the broader role of disease in wild dog population dynamics (Creel & Creel, 2002: 270). We see in other parks like Selous Game Reserve, disease makes up only 4% of all wild dog deaths (Creel & Creel 1997: 4). It s important to consider results case-by-case and apply findings to the bigger picture when appropriate. There is enough research available to support the findings from my research, but as the general African Wild Dog population is further threatened, more research will better future 14

15 conservation measures. For now, I am left wondering a few questions What are the consequences of vaccinating and relocating populations? With the large home ranges that wild dogs have, will these populations just end up outside of the park again? Additionally, with human population growth, what measures can be put in place to protect this species from the impacts of human behavior? I look forward to learning more about African Wild Dogs and hope for good news for the future of this population. 15

16 Works Cited Africa's Wild Dogs. (1999, May). National Geographic, 195(5), Burrows, R., Hofer, H. and East, M.L., Demography, extinction and intervention in a small population: the case of the Serengeti wild dogs.proceedings of the Royal Society of London B: Biological Sciences, 256(1347), pp Burrows, R., Hofer, H. and East, M.L., Population dynamics, intervention and survival in African wild dogs (Lycaon pictus). Proceedings of the Royal Society of London B: Biological Sciences, 262(1364), pp Creel, Scott, and Nancy Marusha. Creel. The African wild dog: behavior, ecology, and conservation. Princeton University Press, Creel, S. and Creel, N. M. (1999), Six ecological factors that may limit African wild dogs, Lycaon pictus. Animal Conservation, 1: 1 9. doi: /j tb00220.x Cleaveland, S., Mlengeya, T., Kaare, M., Haydon, D.A.N., Lembo, T., Laurenson, M.K. and Packer, C., The conservation relevance of epidemiological research into carnivore viral diseases in the Serengeti. Conservation Biology, 21(3), pp Dwyer, Colin. Democracy By Sneeze: When Wild Dogs Must Decide, They Vote With Their Noses. NPR, NPR, 7 Sept. 2017, -not-just-snot-it-s-a-way-to-vote. Gascoyne, S. C., Laurenson, M. K., Lelo, S., & Borner, M. (1993). Rabies In African Wild Dogs (Lycaon Pictus) In The Serengeti Region, Tanzania. Journal of Wildlife Diseases,29(3), Ginsberg, J. R., et al. Local Extinction in a Small and Declining Population: Wild Dogs in the Serengeti. Proceedings of the Royal Society B: Biological Sciences, vol. 262, no. 1364, 1995, pp , doi: /rspb Masenga, E.H., Jackson, C.R., Mjingo, E.E., Jacobson, A., Riggio, J., Lyamuya, R.D., Fyumagwa, R.D., Borner, M. and Røskaft, E., Insights into long-distance dispersal by African wild dogs in East Africa. African Journal of Ecology, 54(1), pp Masenga, E. H., Lyamuya, R. D., Nyaki, A., Kuya, S., Jaco, A., Kohi, E.,... & Røskaft, E. (2013). Strychnine poisoning in African wild dogs (Lycaon pictus) in the Loliondo game controlled area, Tanzania. Int. J. Biodivers. Conserv, 5(6), Rates and causes of mortality in endangered African wild dogs Lycaon pictus: lessons for management and monitoring. Oryx, 41(2), pp

17 Serengeti Wild Dogs Conservation Project Conservation, General. Singita, 24 Mar. 2017, singita.com/conservation-singita/serengeti-wild-dogs-conservation-project/. Woodroffe, R., Davies-Mostert, H., Ginsberg, J., Graf, J., Leigh, K., McCreery, K., Robbins, R., Mills, G., Pole, A., Rasmussen, G. and Somers, M., Woodroffe, R. and Donnelly, C.A., Risk of contact between endangered African wild dogs Lycaon pictus and domestic dogs: opportunities for pathogen transmission. Journal of applied ecology, 48(6), pp Woodroffe, R. & Sillero-Zubiri, C Lycaon pictus. The IUCN Red List of Threatened Species 2012: e.t12436a UCN.UK.2012.RLTS.T12436A en Vucetich, J.A. and Creel, S., Ecological interactions, social organization, and extinction risk in African wild dogs. Conservation biology, 13(5), pp