Free Essay: Tracing Migration Patterns of Terrestrial Animals Using Stable Isotopes

Isotopic analysis is a common method in modern ecological investigations and in studying animal migration. Application of this technique in the field of science, especially in archaeology, can provide fundamental information of not only how species work but also in understanding ecosystems that existed thousands of years ago. Carbon isotopes can be used specifically to distinguish plants that used different photosynthetic pathways such as C3, C4, and CAM. C4 and CAM pathways often lead to a lower carbon fractionation than C3 photosynthetic pathways because of their specialized structures. C4 have a structure called bundle sheath that allows them to increase CO2 concentration. Due to the presence of the specialized structure, C4 plants do not discriminate against a particular carbon isotope like CAM plants with their temporal adaptation (Kelly et al., 2000). Based on the differences in carbon isotope ratios that these different photosynthetic pathways create one can reconstruct migratory patterns of herbivores.

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Dietary determinations can be made from tissue analysis using carbon isotopes based on the isotopically distinct plant groupings that form the animal's diet. Tropical and subtropical grassland environments consist mostly of C4 grasses. On the other hand, temperate grassland environments are mainly made up of C3 plant species (Keegan, 1989). When herbivores feed on a plant, they acquire the carbon isotope signature from that particular plant. As herbivores migrate around to other regions, they acquire the isotope signatures of the plants in the different food webs. Based on the isotope ratios, animals retain information of the feeding locations they have been at. Each environment has its unique carbon isotope signature that represents the plants that can be found in that region. After performing isotope analysis on a tissue, one compares the results to the carbon isotope signature of the environment to figure out where the animal has been feeding at and to reconstruct its migratory routes (Hobson, 1999).

It can be quite challenging when using isotope analysis for paleontology. Although the process of isotope analysis to determine migratory routes is quite simpler, there are a few challenges that may be encountered. One of the challenges is correctly reconstructing the local environment based on the isotopes found in the tissue. As earlier seen, one can determine what type of plants the animal has been feeding on based on the results. Therefore, for this to be the case isotopes should be correctly identified; otherwise reconstructing the environment will not be possible (Hobson, 2005). Another problem is the recovery of isotope data through bones. Isotope signatures in bones can be altered when they get buried in the ground. Paleontologists have to go through a specialized procedure to purify and extract the correct isotope signature from the sample tissue.

Nonetheless, successful isotope analysis can lead to fascinating results for the researchers. For example, a group of paleontologists was able to find several bison bones that dated back to seven thousand years ago in a region of Canada called Albania. This huge finding represented an opportunity to know how the local environment was and the feeding habits of prehistoric bison. Paleontologists were able to perform carbon isotope analysis on the bone samples, and the average bone value of around -18 parts per thousand (Leyden et al., 2001). The results correspond to values mostly found in C3 plants. C3 plants tend to have a higher carbon isotope discrimination rate compared to other photosynthetic pathways, and that is why it has high negative values. The paleontologists thus concluded that bison was mostly feeding on C3 plants seven thousand years ago (Leyden et al., 2001). However, modern understanding of bison is that it is unselective in the type of grass it consumes. This is because of its huge size which makes it graze indiscriminately feeding on a wide variety of grass. As a result, bison tends to have carbon isotopes signatures that represent a variety of different plants. Since the carbon isotopes signatures found in the bones of prehistoric bison had high negative values, it is thought that the region mostly had C4 plants. To reconstruct the migration pattern of bison thousands of years ago, there have to be more bison bone discoveries. It is imperative to compare the carbon isotope values of more bison bones in to decisively determine the migration routes and how the environment was in the region.

Other important isotopes used to determine migration patterns of animals are hydrogen and oxygen isotopes. The abundance of the hydrogen and oxygen isotopes throughout different regions is well established. For example, water is composed of two hydrogens and one oxygen, but their isotopes can vary. A water molecule can be composed of 1H or 2H and same goes for the oxygen. The most common oxygen isotopes are 18O and 16O (Clark & Fritz, 2013). It means that a water molecule can be composed of a combination of any of the mentioned isotopes. Mostly, water molecules that are composed of heavier isotopes tend to be found in the coastal region because they are the first ones to fall from the clouds. As clouds move into the continent, the isotope signature becomes more negative, meaning the lighter isotopes are the ones that remain behind (Clark & Fritz, 2013). Based on this pattern, each body of water will have its particular isotope signature depending on the location. When animals drink water, they acquire the isotope signature of that particular body of water. Animals retain information of the location where they have been feeding and drinking water. This is particularly helpful when investigation animals that migrate throughout for long distances such as birds. Based on the isotopes found in the water molecules one can easily reconstruct the migration pattern for such an animal.

Leapfrog migration refers to the migration pattern where birds travel to the southern part of a region. Birds often travel thousands of miles during this migration to find an area to reproduce. Wilson Warblers is an example of birds that take part in the leapfrog migration (Kelly et al., 2002). Knowing the migration routes and patterns of birds as well as other animals is crucial to conservational efforts. It helps the conservationists to know where birds and animals reproduce so that such areas can be conserved to minimize disturbance and allow the species to procreate. Notably, most birds and animals have been extinct because humans have interfered with their natural habitats where they usually reproduce (Engen & Saether, 2017). Understanding the migration routes of birds and animals allows conservationists to focus on such areas that are important for reproduction and protect them to allow species to undertake their reproduction processes and prevent extinction. Also, isotope analyzes are helpful in the investigation of migratory patterns of birds that take part in leap migration as they have a high mobility that makes it difficult to trace their migration routes using other methods. The importance of knowing the migration patterns for animals cannot be underestimated. The applications that one can derive from reconstructing the migration routes of species is fundamentally important to many ecological areas and with isotope analyzes one can easily do so. Many species are not well studied, and it is extremely important to educate the population on how humans are impacting the different ecosystems. Isotope analysis allows people to figure out the migration patterns for many terrestrial species including those that lived thousands of years ago.

References

Clark, I. D., & Fritz, P. (2013). Environmental isotopes in hydrogeology. CRC press.

Engen, S., & Saether, B. E. (2017). Extinction Risk and Lack of Evolutionary Rescue under Resource Depletion or Area Reduction. The American Naturalist, 190(1), 73-82.

Hobson, K. A. (1999). Tracing origins and migration of wildlife using stable isotopes: a review. Oecologia, 120(3), 314-326.

Hobson, K. A. (2005). Using stable isotopes to trace longdistance dispersal in birds and other taxa. Diversity and Distributions, 11(2), 157-164.

Keegan, W. F. (1989). Stable isotope analysis of prehistoric diet. Reconstruction of Life from the Skeleton, 223-236.

Kelly, J. F. (2000). Stable isotopes of carbon and nitrogen in the study of avian and mammalian trophic ecology. Canadian Journal of Zoology, 78(1), 1-27.

Kelly, J. F., Atudorei, V., Sharp, Z. D., & Finch, D. M. (2002). Insights into Wilson's Warbler migration from analyses of hydrogen stable-isotope ratios. Oecologia, 130(2), 216-221.

Leyden, J. J., & Oetelaar, G. A. (2001). Carbon and nitrogen isotopes in archeological bison remain as indicators of paleoenvironmental change in southern Alberta. Great Plains Research, 3-23.