Global biodiversity is increasingly under threat and species loss has prompted the argument that our natural world is experiencing a sixth major extinction event (Pimm & Brooks, 2000). Predators are especially vulnerable to extinction as they suffer population losses from many sources such as human–wildlife conflict, over-hunting, decline in prey and habitat loss. (Gaona, Ferreras & Delibes, 1998; Woodroffe, 2000; Treves & Karanth, 2003; Whitman et al., 2004). Parasites are increasingly linked to population impacts in wild felid and canid species (Pedersen et al., 2007). Many predator species exist in small and fragmented populations, vulnerable to stochastic events and other ongoing sources of population loss, which can drive them locally, if not globally, extinct. The Iberian lynx is a key example of an imperiled predator and is currently the most endangered felid in the world (Nowell & Jackson, 1996; Baillie, Hilton-Taylor & Stuart, 2004). This species may lose the survival battle without intense and continued conservation intervention.
In their paper, López et al. (2009) provide an excellent example of endangered species management, which demonstrates the importance of long-term population monitoring programs and the effectiveness of careful intervention design. Through their monitoring program, the authors identify the emergence of feline leukemia virus (FeLV) in the core population of Iberian lynx on the Iberian Peninsula. This pathogen is commonly found in domestic cats, which are considered the primary host (Arjona et al., 2007). While previous low-level FeLV exposure had been identified in the Iberian lynx population before the 2007 outbreak (Luaces et al., 2008; Meli et al., 2009), no associated mortality or other impacts had been identified. Then, inexplicably, FeLV emergence in 2007 causes an outbreak with mortality levels that threaten the survival of the species. Viral sequence from the 2007 outbreak is distinct from previous infections in the population but consistent with transmission from locally infected cats (Meli et al., 2009). In response to the outbreak, a FeLV control program is undertaken by the authors and other partners, which utilizes a test, removal and vaccination approach in Iberian lynx coupled with reduction of the sympatric feral cat population. It is successful and FeLV-associated mortality in the Iberian lynx ceases.
What can we learn from the approach taken by López and colleagues? Firstly, intervention for the Iberian lynx disease outbreak is designed and implemented through a partnership approach between many national stakeholders, project participants and experts. Often in wildlife management crises, consultation and inclusiveness of stakeholders is avoided in order to streamline processes and expedite action. But this can backfire when partner agencies and stakeholders are required in downstream management activities. This paper serves as a reminder that wildlife management is better implemented inclusively rather than exclusively.
Secondly, this study demonstrates the dynamic and unpredictable nature of pathogen invasion outcomes in a population. In this case, FeLV invasion in the population was not identified as an important problem but this changed dramatically in the 2007 outbreak. This highlights the danger of defining the threat level of a pathogen for a species. It is becoming clearer that pathogen behavior can vary widely between species, and within and between populations over space and time. A number of factors influence pathogen invasion outcomes as they operate and interact at the level of the host, pathogen and/or the environment, which can influence host susceptibility and/or pathogen virulence and change the nature of an outbreak in a susceptible host population (Hudson et al., 2002). Thus, as in forensic sciences, we are reminded to be cautious with ‘pathogen profiling’ or reliance on expected behavior of a pathogen, as seen here in the divergent nature of FeLV invasion in Iberian lynx or for example, distemper outbreaks in African wild dogs in Botswana (Alexander et al., 1996; Alexander et al., 2008)
The Iberian lynx story also exemplifies the cascading interactions of infectious disease within ecological communities and underscores the importance of infectious disease in ecosystem-wide processes. The decline of the Iberian lynx is linked to the disappearance of their primary prey species, the wild rabbit Oryctolagus cuniculus (Ferrer & Negro, 2004) due to the emergence of Myxomatosis virus in the 1950s and Rabbit Hemorrhagic Viral Disease in the 1980s (Delibes-Mateos, Ferreras & Villafuerte, 2008). Disease-related loss of prey and consequent reduction in the Iberian lynx population has now made this species, in turn, more vulnerable to infectious disease-mediated extinction risks. Had the population been as large as that before the disease-related decline of their prey, it is less likely that this FeLV outbreak would have posed a threat to survival of this species.
Lastly, the importance and value of long-term population monitoring cannot be over emphasized. Long-term monitoring allows population threats to be identified, intervention action taken and success measured against important baseline data. In most cases in wildlife management, we are operating in the dark; we lack funding to properly monitor both the population under question and our intervention outcomes. We are, more often than not, unsure of the long-term effects of our management actions. In short, while we might have significant theoretical assessments, we are often short on empirical studies that provide concrete insight into the control of infectious disease in endangered species. Studies such as this, conducted on a long-term basis, coupled with experimental and modeling approaches, can support the identification of a mechanistic understanding of disease invasion outcomes. This is ultimately the information required if we are to succeed in managing infectious disease threats to endangered species.