Thursday, July 9, 2009

Taking a Bite out of Niche Conservatism

In efforts to quash assumptions associated with niche conservatism, scientists from the Florida Museum of Natural History and the New York State Museum have enlisted the teeth of several fossil mammals to better understand the ecology of climate change.

Recently published at PLoS One, the research holds critical the idea that niches remain constant over extended periods of time. This idea, called niche conservatism, essentially holds that niches are highly specialized, ancestrally –linked, relatively inflexible and are therefore exceedingly susceptible to disturbance and rapid degradation in the face of change - particularly climate change.

While biologic response to environmental change is assumed, often such conservatism is overemphasized and is presented in a manner inconsistent with understanding gained through modern ecology and the insights of paleontology, which have both demonstrated incredible plasticity within the Earth’s biota.

Undoubtedly, the changing climate is of great concern and poses tremendous challenges to all organisms, but at the same time life is flexible and extinctions are not entirely unavoidable. As evidence to life’s flexibility, the currently discussed paper uses the testimony of change documented in the isotopic signatures of mammalian tooth enamel to show that the obstacle of climate change has been successfully negotiated in the past. More specifically, glacial-interglacial transitions during the Pliocene and Pleistocene are marked by substantial alterations in plant communities; however the contemporaneous uptake of vegetative food-stuffs by mammals seems to have fluctuated little.

The article is worth a read:
DeSantis, L., Feranec, R., & MacFadden, B. (2009). Effects of Global Warming on Ancient Mammalian Communities and Their Environments PLoS ONE, 4 (6) DOI: 10.1371/journal.pone.0005750

Vertebrates, and in particular mammals, are highly responsive to changes in the environment. Climate fluctuation can lead to an incredible amount of variation in the diet choice, distribution, and even the morphology of vertebrates.

Natural selection is a reflection of the biological and physical environment as transcribed into the genes of flora and fauna; however, the DNA found within living cells functions only as a recipe for ecological fit, the actual ingredients – the building materials - required to construct living tissue are harvested from surrounding chemistry. Because of variability inherit to this chemistry, the isotopic constituents that compose individuals may differ with respect to climate, diet, or a number of other variables.

For example, carbonate apatite - a primary constituent of both skeletal bones and dentition in vertebrates - is incorporated into organisms through diet and water uptake. Some conservationists use the isotopic signatures recovered from this apatite to better decipher the life histories of contemporary species in expectation of aiding in their continued preservation. As a case in point, remains from the world’s largest cavefish (Milyeringa veritas) have been used by Australian conservationists to better examine and comprehend the environment and ecosystem inhabited by the fish. The cavefish resides in deep water columns that are rich in dissolved limestone. Due to relative densities and variable solubility, different depths in the water column are correlated to specific concentrations of dissolved materials. By examining the isotopic signatures of the cavefish’s skeletal apatite, conservationists were able to discover the exact depth the fish occupies.

As demonstrated by the cavefish, uptake of elements within vertebrates (O, C, Sr & others) generates a highly detailed record of the environmentally available isotopes at a given point in time; this availability can even be indicative of climate.As another illustration of application, Thure Cerling and others at the University of Utah have refined the technique of laser ablation to such quality and precision that they can use it to vaporize the apatite found in teeth. They then analyze the resulting gas via spectrometry to determine its isotopic components. The teeth can be examined to such resolution as to be able to report the dietary preferences of mammals between C3 and C4 plants. A similar isotopes-from-enamel strategy was employed by the folks from the University of Florida to expound several fallacies of niche conservatism…

Examinations of isotopic records are commonplace for many paleontologists. Uncountable volumes have been written on Foram O-18 isotopes and their relationship to periods of increased glaciation, and similar correlations of speleothems and C-13, but accurate isotopic records of both of these elements can be obtained from other sources as well - including mammals.

As a side note - skeletal tissues, which possess apatite, are very susceptible to diagenic processes that can cause recrystalization and alter results, but dental samples seem to be far more reliable when it comes to maintaining their original isotopic signatures. This coupled with the knowledge acquired in the past few decades in regarding incorporation of specific O-18 and C-13 isotopes into biological entities has brought to light a highly accurate record of climate change – and the critters that adapted to it.

1 comment:

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