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There is an ongoing debate in all fields related to the conservation of endangered species, and one which will probably never come to a final resolution. It concerns the impact that handling has on wildlife populations, as well as the effects that marking and collaring animals has on their behavior and survival.
A few studies have demonstrated that altering the morphology of an animal with man-made markings or devices to study that animal can have measurable effects on behavior, and even reproductive success.
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Negative Effects of Invasive Sampling Methods
Animals are marked in order to perform mark-recapture studies, used to estimate population abundance and density of specific populations. Marking consists of exactly what the name implies; adding some kind of distinguishing mark, often a bright color, to an animal. Sometimes these markings and tracking devices may be quite conspicuous and they often come with consequences. Studies have shown, for example, that birds possessing colored bands are actually more attractive to mates.
Animals can also be affected internally by human study techniques. When animals are handled, levels of stress hormones increase and this can lead to a variety of consequences, such as the depression of immune functions. This could make an organism more susceptible to disease or other latent ailments, leading to sickness and potentially death. An outcome like this is especially disturbing in threatened or endangered species.
Furthermore, human study techniques could alter an animal’s behavior. An animal who has had a particularly traumatic experience during handling may avoid the location where it was trapped, leading to that animal becoming “trap shy". If the area being avoided is an important dispersal corridor or an area rich in food or mates, that animal could suffer from avoiding it. An animal that was lured into a trap by food and perceives that the food reward was worth being poked and prodded may become “trap happy" and frequent areas where it has been trapped, perhaps disturbing the resident fauna and flora. In addition, animals that are trap happy or trap shy tend to distort researchers’ views of population numbers and estimates.
Other, even more serious problems include outright harming animals (albeit without malice) through the use of data-gathering methods. Some tracking devices have been implanted in animals and in a number of cases these malfunctioned and risked causing the animals severe illness and even death. Many early studies based on molecular biology techniques required a great deal of genetic information that necessarily meant the destruction of the animal being sampled.
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Non-Invasive Sampling to the Rescue. Kind of.
Due to the unacceptability of these results, biologists created an approach that would minimize any potential harm to the animals being observed. The result was non-invasive sampling.
In the articles “What is Molecular Ecology" and “Using Genetics in the Conservation of Endangered Species," we discussed the new tools that scientists are using to study wildlife populations - mainly genetics - and the huge variety of information that can be gleaned from those tools. Non-invasive sampling is the method by which scientists gather the genetic material. At this point in time, scientists have been able to obtain genetic material from:
- Owl pellets (which are essentially bits of undigested and regurgitated skin, fur, saliva and bones of animals that the owl has eaten)
- Eggshell membranes
- Snake skin
- Sloughed off whale skin
The most commonly used sources of DNA in non-invasive sampling studies are feces and hair. Fecal samples contain a high number of sloughed intestinal epithelial cells, which contain the DNA of the organism doing the defecating. The benefit of fecal samples, in addition, is that you can get DNA of prey items as well, and so you can analyse a predator’s diet as well as study the presence and abundance of prey species. Hair samples, on the other hand, give you information only on the animal to which the hair belongs; DNA is extracted from cells in the root of the hair.
Scientists have been quite crafty in their collection of non-invasive samples. They have obtained DNA from coyote saliva from scented lures that were chewed on. They have placed double sided sticky tape at the entrances of bear and wombat burrows to collect hair samples when the animals exit their burrows. They have skillfully collected plumes of feces from the water after dolphins defecate. Some researchers have also been able to use blood sucking insects, like the Kissing Bug, to collect blood samples non-invasively. In none of these studies were the animals handled, and in many of them, human researchers went nowhere near the wildlife. Furthermore, non-invasive sampling is essential in cases where particular species are highly elusive or move over vast territories.
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Problems with Non-Invasive Sampling
While obtaining genetic material from non-invasive sources has obvious benefits with regards to minimizing impacts on wildlife, there are still problems with the technique when the time comes to analyze the data in the lab. Non-invasive sampling was made possible by the elaboration of the Polymerase Chain Reaction, or PCR, one of the most fundamental processes performed in huge numbers of labs around the world; essentially, what PCR does is produce millions of copies of a particular DNA sequence starting from a very minute quantity of DNA, sometimes even a single molecule.
Often, when performing PCR on DNA extracted from non-invasive samples, there is the possibility of “allelic dropout", or the failure of the PCR technique to amplify (i.e. make many copies of) one of the alleles in a heterozygote, thereby giving the false impression that an individual is a homozygote. Furthermore, there can be “aberrant alleles", or mistakes in the PCR amplification process. Contamination can also be a problem with non-invasive samples.
These errors are being worked out as more and more studies are including non-invasive sampling components. Though these sampling techniques might not completely supplant other, more traditional techniques used in wildlife conservation research, they provide a welcome alternative to use in cases where direct contact with wildlife species is not possible or not recommended.
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L.P. Waits and D. Paetkau. "Non-invasive Genetic Sampling Tools for Wildlife Biologists: A Review of Applications and Recommendations for Accurate Data Collection." Journal of Wildlife Management. 2005.
S.D. Hoyle et al. "Demographic monitoring of an entire species, the northern hairy-nosed wombat (Lasiorhinus krefftii), by genetic analysis of noninvasively collected material." Animal Conservation. 2003.
S.C. Minta and K.S. Heinemeyer. "DNA-based analysis of hair to identify species and individuals for population research and monitoring." Wildlife Society Bulletin. 1997.
P. Taberlet et al. "Non-invasive Genetic Sampling: Look Before You Leap." Trends in Ecology and Evolution. 1999.
P. Taberlet and G. Luikart. "Non-invasive Genetic Sampling and Individual Identification." Biological Journal of the Linnean Society. 1999.
Conservation of Wildlife Populations: Demography, Genetics, and Management (Mills, 2006).