1. 1. Life History Strategies Essay - UP677529 LIFE HISTORY STRATEGIES, RPPELLS VULTURE (Gyps rueppellii) AND INCREASED THREATS TO THE SPECIES SURVIVABILITY Interpreting the way in which different organisms utilise specific traits to survive and reproduce can be aided by the theoretical Darwinian Demon (Ferretti et al, 2005). An example of unlimited exponential growth, this hypothetical organism would produce infinite offspring as soon as it was born and would have ultimate levels of fitness, in a conjectural situation where evolution was wholly unimpeded (Hughes et al, 2002). In reality, various factors influence the life history strategies, or traits an organism possesses and utilises, in order to maximise its survivability (Mueller et al, 2001). The theory of life history strategy is founded on the idea that available resources in an environment are limited and certain characteristics such as, the reproductive lifespan of an animal, age of sexual maturity and the quantity and size of progeny produced are also deliberated (Roff, 2007). As resources available to an individual are finite in almost any given environment, the amount of energy and time given to one life strategy will reduce the amount of time and energy available for another (Bamford et al, 2009). As with Darwinian Theory, it is the specific combination of adaptations and traits displayed by a species that determine its overall survivability, and the extent to which a species can produce numerous, viable offspring (Antor et al, 2007). In his book, Ecological Adaptations for Breeding in Birds (1968), evolutionary ecologist Lack, D. advocated the theory that reproductive yield in avian species reflected their various adaptations to environmental factors, including available resources and predation risk, with subsequent studies adding further credence to the concept (Silby et al, 2012; Roff, 2007). Silby et al (2012), propagated that calculable trade-offs in energy allocation between different avian species would be the result when environmental confines were placed on energy supply, and similarly, when physiological constraints limited metabolic energy expenditure. The result of this study, along with separate investigations into demographic stochasticity and population viability in various avian species by Robert et al (2004) and Roff (2007), suggest that (i) as parental care in a species increases, reproductive output decreases, thus indicating the energy exchange between egg production and hatchling nurture and development, (ii) a high mortality rate is compensated for by a species investing in a high rate of reproduction output, (iii) and the amount of energy given to reproduction is dictated by mass-specific metabolic rate, indicating that with an increased body mass, reproductive rate usually decreases. This theory is significant when applied to the Rppells vulture (Gyps rueppellii) (Brehm, A., 1852), as the monogamous parent birds are an iteroparous, annually breeding species, that invests heavily in raising only one to two chicks in a single year (Ramreza et al, 2011). G. rueppellii is not sexually dimorphic and with a wingspan up to 8.5 feet wide, both males and females can reach up to nine kilos in weight (Ruxton & Houston, 2004). Consequently, the idea that an increase in body mass results in reduced reproductive output could indeed be applied to G. rueppellii (Weber et al, 2009). 1
2. 2. Life History Strategies Essay - UP677529 Expanding on the concept of life history strategies, MacArthur & Wilson (1967) hypothesised that selective pressures drive evolution in two distinctly separate directions (Coulson et al, 2010). Using ecological algebraic terminology, (r)selection (r representing high production or turnover), generally indicated a species that displayed traits such as small body mass, early maturation, short generation time, high fecundity rates and wide progeny distribution (Cardona et al, 2009). Whereas (K)selected species (K representing the carrying capacity of a population), commonly exhibited a large body mass, later age of maturation, longer generation time and extensive parental care given to fewer offspring for a longer period of time (Grande et al, 2009). Through their work on The Theory of Island Biogeography (1967) MacArthur & Wilson theorised that although different species may physically co-inhabit the same environment, that particular environment may affect each individual species in an entirely different way, encouraging wholly different traits and life strategies (Lancaster et al, 2008). They suggested that (r)-selected individuals were more likely to face an unpredictable or fluctuating environment, such as that of a small prey species for example, which would render competitive traits among a species unnecessary, and instead favour high reproduction rates (Londei, 2010). Conversely, (K)-selected species, would exist around maximum carrying capacity in a relatively stable environment, requiring a species to adapt in order to successfully compete intra-specifically for limited resources (cite). In (r)/ (K)-selection theory, G. rueppellii could be identified as a predominantly (K) selective species (Virani et al, 2012). With G. rueppellii, parent birds equally share incubation responsibilities for up to 58 days, and after hatching, both birds provide parental care for an additional 90 day period until the chick is able to survive unassisted (Virani et al, 2012; Rose & Charlesworth, 1980). G. rueppellii have been recorded travelling distances of up to 150 kilometres away from a nest site in order to procure food for their chicks, and will store this food in their crops to regurgitate to the chick upon their return (Satheesan & Satheesan, 2000). Although as a (K)-selected species adult G. rueppellii are competitive inter and intra-specifically, to avoid predation and maximise infant mortality the species is colonial, nesting on cliffs in mated pairs up 100 strong in close proximity (Margalida et al, 2003). While G. rueppellii invest a significant amount of energy into rearing often only one chick, they increase their species continued survival rate by adopting a perennial breeding lifestyle as a monogamous pair, and will often reproduce every year, as long as there are sustainable resources to allow for breeding (Oro et al, 2008). Virani et al (2012) monitored a nest site of G. rueppellii in Kwenia between 2002 and 2009, and found that breeding was intrinsically related to rainfall in the previous year, and in turn, to ungulate migration of the Mara-Serengeti, which provided vital foraging ground for the scavenging species. G. rueppellii are a long lived species, often reaching an age of 50 years old in the wild (IUCN, 2013). The species does not reach sexual maturity until approximately five years old, insuring the animal has more chance of reaching optimal fitness and an ability to obtain food successfully before breeding (Anadn et al, 2010). Developing adequate scavenging skills ensures adult G. 2
3. 3. Life History Strategies Essay - UP677529 rueppellii are able to provide optimal levels of parental care to their progeny (Johnson et al, 2006). G. rueppellii frequently encounter other species of vulture, as well as jackals (Canis aureus) and spotted hyenas (Crocuta crocuta) at carcasses, and a number of intra and inter-specific interactions have been documented (Durieza et al, 2012). Mediation of competition via a trade-off in traits can enable co-existence between different species, and Pennycuick (2008) identified certain mechanisms between G. rueppellii and other vulture species, that reduced intra-specific competition. Social vultures of the Gyps genus, dominate carcass feeding sites when migratory ungulates are present in the dry season, which in turn causes smaller species such as the white headed vulture (Trigonoceps occipitalis) to employ an entirely different feeding and breeding strategy to avoid direct competition with larger vultures of the Gyps genus (Carrete et al, 2006). T. occipitalis lay their eggs between June and August, whilst G. rueppellii and Lappet-faced vultures (Torgos tracheliotos) for example, lay their eggs between February and May, and so raise their young at different times, reducing the potential for intra-specific conflict (Pennycuick, 2008). However, T. tracheliotos and G. rueppellii commonly coincide in raising their young and Kendall et al (2012) propose that Lacks theory of adaptation could explain how these two species avoid conflict. T. tracheliotos are solitary birds which do not nest in colonies and avoidance of competition between G. rueppellii and T. tracheliotos could primarily be due to a larger body mass in T. tracheliotos encouraging successful niche-separation (Selva & Fortuna, 2007). The inter-specific relationship between G. rueppellii and C. crocuta is also noteworthy, as it suggests commensalism, or facultative symbiosis on the part of G. rueppellii, with the morphology of C. crocuta being better adapted for tearing openings in flesh which the beaks of G. rueppellii are less well modified for (Durieza et al, 2012). Consequently, G. rueppellii are documented as waiting for an opportunity to feed on the cavities in carcass flesh provided by C. crocuta (Kendall, 2013). G. rueppellii has evolved to occupy an ecological niche as an obligate scavenger, totally dependent on carcasses for food (Shivik, 2006). Large individual body mass is selected for generationally if availability of carrion is infrequent, as it is for G. rueppellii particularly in the wet season, which allows the species to survive on body reserves in the periods between discovering food falls (Kendall et al, 2014). Subsequently, flight patterns and behaviour are also altered evolutionarily, and a heavy body mass necessitates soaring over flapping in flight, reducing speed and as a result, the energy costs of long distance transport (Ruxton & Houston, 2004). Due to this specialisation in high altitude soaring as a low energy form of flight, G. rueppellii have evolved away from an agile morphology that would facilitate hunting prey of their own (Koenig, 2006). Niche separation and specialisation such as that employed by G. rueppellii, have made them and related species successful worldwide (Thiollay, 2006). Vultures occupy a position in the ecosystem that is analogous to no other species, and they play an essential role in food cycles by improving nutrient recycling and the stability of populations in their environment (Selva & Fortuna, 2007). The important role vultures play ecologically was highlighted by the inadvertent poisoning of millions of 3
4. 4. Life History Strategies Essay - UP677529 Indian vultures (Gyps indicus) and other vulture species across Asia in recent decades, as a result of livestock being administered with the veterinary drug Diclofenac, a non-steroidal anti- inflammatory drug (NSAID) (Cuthbert et al, 2007). The decline of vulture species as a result of this abiotic/anthropogenic factor has had a significant knock-on effect to the environment and the human populace (Anderson et al, 2006). Carcasses, once utilised as food by vultures, rot in fields and contaminate drinking water (Cuthbert et al, 2007). In the absence of vultures, species such as rats and dogs have partially replaced them at carcasses, but the digestive abilities of these species are hugely inefficient by comparison to vultures, whos highly acidic, specialised digestive system has the ability to kill any pathogens during transit (Kendall & Virani, 2012). Thus, diseases such as anthrax and rabies are on the increase in Asia, and it is thought that over 30,000 people die of rabies in India alone every year as a direct result of vulture decline (Kendall & Virani, 2012). Similarly, use of NSAIDS in livestock, as well as pesticides, over hunting and persecution for trade of meat and body parts in recent years in Africa, has seen vulture numbers significantly fall (Thiollay, 2006). With these new environmental pressures, the life history strategies employed by G. rueppellii that successfully established them in their ecosystem may no longer be viable for the species prolonged survival, unless conditions are restored. Hypothetically, if the risk is not eliminated for G. rueppellii, it may be more sustainable for this (K)-selected species to adopt some (r)-selected traits to increase survivability, such as an increase in the number of breeding events and egg clutch size, for example. However, continued monitoring of significant G. rueppellii nest sites, as well as breeding and reintroduction programmes by conservationists are currently attempting to restore previous environmental stability, as threats to the species survival are comparable to a stochastic event, and it is unlikely the species could adapt to the changing environmental circumstances in time. Word count: 1638 4
5. 5. Life History Strategies Essay - UP677529 REFERENCES Anadn, J., D., Snchez-Zapata, J., A., Carrete, M., Donzar, J., A. & Hiraldo, F. (2010). Large- scale human effects on an arid African raptor community. Animal Conservation, Volume 13(5). 495-505 Anderson, M., D., Piper, S., E. & Swan, G., E. (2005). Non-steroidal anti-inflammatory drug use in South Africa and possible effects on vultures. South African Journal of Science, Volume 101(3-4). 112-114 Antor, R., J., Margalida, A., Frey, H., Heredia, R., Lorente, L. & Ses, J., A. (2007). First Breeding Age in Captive and Wild Bearded Vultures Gypaetus barbatus. Acta Ornithologica, Volume 42(1). 114-118 Bamford, A., J., Monadjem, A., Anderson, M., D., Anthony, A., Borello, W., D., Bridgeford, M., Bridgeford, P., Hancock, P., Howells, B., Wakelin, J. & Hardy, I., C., W. (2009). Trade-offs between specificity and regional generality in habitat association models: a case study of two species of African vulture. Journal of Applied Ecology, Volume 46(4). 852-860 Cardona, M., Colomer, A., Prez-Jimnez, M., J., Sanuy, D. & Margalida, A. (2009). Modelling Ecosystems Using P Systems: The Bearded Vulture, a Case Study. Lecture Notes in Computer Science, Volume 5391. 137-156 Carrete, M., Jos A Donzar, J., A., Margalida, A. & Bertran, J. (2006). Linking ecology, behaviour and conservation: does habitat saturation change the mating system of bearded vultures? Biology Letters, Volume 2(4). 624-627 Coulson, T., Tuljapurkar, S. & Childs, D., Z. (2010). Using evolutionary demography to link life history theory, quantitative genetics and population ecology. Journal of Animal Ecology, Volume 79(6). 1226-1240 Cuthbert, R., Parry-Jones, J., Green, R., E. & Pain, D., J. (2007). NSAIDs and scavenging birds: potential impacts beyond Asia's critically endangered vultures. Biology Letters, Volume 3(1). 91-94 Durieza, O., Herman, S. & Sarrazin, F. (2012). Intra-specific competition in foraging Griffon Vultures Gyps fulvus: 2. The influence of supplementary feeding management. Bird Study, 59(2). 193-206 5
6. 6. Life History Strategies Essay - UP677529 Ferretti, V., Llambas, P., E. & Martin, T., E. (2005). Lifehistory variation of a neotropical thrush challenges food limitation theory. Proceedings of the Royal Society of Biological Sciences, Volume 272(1564). 769-773 Grande, J., M., Serrano, D., Tavecchia, G., Carrete, M., Ceballos, O., Daz-Delgado, R., Tella, J., L. & Donzar, J., A. (2009). Survival in a long-lived territorial migrant: effects of life-history traits and ecological conditions in wintering and breeding areas. Oikos, Volume 118(4). 580-590 Gyps rueppellii. (2013). Retrieved from the IUCN Red List of Threatened Species website: http://www.iucnredlist.org/details/22695207/0 [Accessed on: 02/02/2014] Hughes, K., A., Alipaz, J., A., Drnevich, J., M. & Reynolds, R., M. (2002). A test of evolutionary theories of aging. PNAS, Volume 99(22). 1428614291 Johnson, J., A., Lerner, H., R., L., Rasmussen, P., C. & Mindell. D., P. (2006). Systematics within Gyps vultures: a clade at risk. BMC Evolutionary Biology, Volume 6(65). 1471-2148 Kendall, C., J. (2013). Alternative strategies in avian scavengers: how subordinate species foil the despotic distribution. Behavioural Ecology and Socio-biology, Volume 67(3). 383-393 Kendall, C., J. & Virani, M., Z. (2012). Assessing Mortality of African Vultures Using Wing Tags and GSM-GPS Transmitters. Journal of Raptor Research, Volume 46(1). 135-140 Kendall, C., J., Virani, M., Z., Hopcraft, J., G., C., Bildstein, K., L. & Rubenstein, D., I. (2014). African Vultures Dont Follow Migratory Herds: Scavenger Habitat Use Is Not Mediated by Prey Abundance. PLOS One, Volume 1317. Kendall, C., Virani, M., Z., Kirui, P., Thomsett, S. & Githiru, M. (2012). Mechanisms of Coexistence in Vultures: Understanding the Patterns of Vulture Abundance at Carcasses in Masai Mara National Reserve, Kenya. The Condor, Volume 114(3). 523-531 Koenig, R. (2006). Vulture Research soars as the scavengers numbers decline. Ornithology, Volume 312. Lack, D. (1968). Ecological Adaptations for Breeding in Birds. London: Methuen & Co. Ltd. Lancaster, L., T., Hazard, L., C., Clobert, J. & Sinervo, B., R. (2008). Corticosterone manipulation reveals differences in hierarchical organization of multidimensional reproductive trade-offs in r- strategist and K-strategist females. Journal of Evolutionary Biology, Volume 21(2). 556-565 6
7. 7. Life History Strategies Essay - UP677529 Londei, T. (2010). The colourful White-headed Vulture Aegypius occipitalis: enhancement of threatening signals for interspecific competition? Ostrich: Journal of African Ornithology, Volume 81(2). 159-162 MacArthur, R., H. & Wilson, E., O. (1967). The Theory of Island Biogeography. USA: Princeton University Press Margalida, A., Garcia, D., Bertrand, J. & Heredia, R. (2003). Breeding biology and success of the Bearded Vulture Gypaetus barbatus in the eastern Pyrenees. Ibis, Volume 145(2). 244-252 Mueller, L., D., Guo, P., Z. & Ayala, F., J. (2001). Density-dependent natural selection and trade- offs in life history traits. Science, Volume 253(5018). 433-435 Oro, D., Margalida, A., Carrete, M., Heredia, R. & Donzar, J., A. (2008). Testing the goodness of supplementary feeding to enhance population viability in an endangered vulture. PLOS One, 1371. Pennycuick, C., J. (2008). Breeding of the lappet-faced and white-headed vultures (Torgos tracheliotus Forster and Trigonoceps occipitalis Burchell) on the Serengeti Plains, Tanzania. African Journal of Ecology, Volume 14(1). 67-84 Ramreza, J., Muoza, A., R., Onrubiaa, A., de la Cruza, A., Cuencaa, D., Gonzleza, J., M. & Arroyoa, G., M. (2011). Spring movements of Rppell's Vulture Gyps rueppellii across the Strait of Gibraltar. Ostrich: Journal of African Ornithology, Volume 82(1). 71-73 Robert, A., Sarrazin, F., Couvet, D. & Legendre, S. (2004). Releasing Adults versus Young in Reintroductions: Interactions between Demography and Genetics. Conservation Biology, Volume 18(4). 1078-1087 Roff, D., A. (2007). Contributions of genomics to life-history theory. Nature Reviews Genetics, Volume 8. 116-125 Rose, M. & Charlesworth, B. (1980). A test of evolutionary theories of senescence. Nature, Volume 287. 141 142 Ruxton, G., D. & Houston, D., C. (2004). Obligate vertebrate scavengers must be large soaring fliers. Journal of Theoretical Biology, Volume 228(7). 431-436 International Bird Strike Committee (2000). Serious vulture-hits to aircraft over the world. Amsterdam: Satheesan, S., M. & Satheesan, M. Selva, N. & Fortuna, M., A. (2007). The nested structure of a scavenger community. Proceedings of the Royal Society of Biological Sciences, Volume 274(1613). 1101-1108 7
8. 8. Life History Strategies Essay - UP677529 Shivik, J. A. (2006). Are Vultures Birds, and Do Snakes Have Venom, because of Macro and Micro scavenger Conflict? Bio Science, Volume 56(10). 819-823 Sibly, R., M., Witt, C., C., Wright, N., A., Venditti, C., Jetze, W. & Brown, J., H. (2012). Energetics, lifestyle, and reproduction in birds. PNAS, Volume 10(1073). Thiollay, J., M. (2006). The decline of raptors in West Africa: long-term assessment and the role of protected areas. Ibis, Volume 148(2). 240-254 Virani, M., Z., Kendall, C., Njoroge, P. & Thomsett, S. (2011). Major declines in the abundance of vultures and other scavenging raptors in and around the Masai Mara ecosystem, Kenya. Biological Conservation, Volume 144(2). 746-752 Virani, M., Monadjem, A., Thomsett, S., I., & Kendall, C. (2012). Seasonal variation in breeding Rppells Vultures Gyps rueppellii at Kwenia, southern Kenya and implications for conservation. Bird Conservation International, Volume 10. 1-10 Weber, R., E., Hiebl, I. & Braunitzer, G. (2009). High Altitude and Haemoglobin Function in the Vultures Gyps rueppellii and Aegypius monachus. Biological Chemistry, Volume 369(1). 241-250 8