Showing posts with label ecology. Show all posts
Showing posts with label ecology. Show all posts

Thursday, April 7, 2011

Evidence of the Benefits of Biodiversity

The following is a press release from NFS - April 6, 2011
View a webcast with Bradley Cardinale of the University of Michigan.

Frequent reports of accelerating species losses invariably raise questions about why such losses matter and why we should work to conserve biodiversity.

Biologists have traditionally responded to such questions by citing societal benefits that are often presumed to be offered by biodiversity--benefits like controlling pests and diseases, promoting the productivity of fisheries, and helping to purify air and water, among many others. Nevertheless, many of these presumed benefits are have yet to be supported by rigorous scientific data.

But Bradley J. Cardinale of the University of Michigan has produced a new study that finally verifies that biodiversity promotes water quality and explains how it does so. Specifically, the study reveals how biodiversity helps remove excess levels of nutrients from streams that commonly degrade water quality.

Cardinale said, "This is the first study that nails the mechanism by which biodiversity promotes water quality. And by nailing the mechanism, it provides solid evidence of a cause-and-effect relationship between biodiversity and water quality that was previously missing."

Here's how Cardinale's mechanism works: as the number of species of algae in a stream increases, the geographical distribution of these organisms within the stream expands, and the more water these widely distributed organisms may cleanse through a pollution-removing process common to algae.

Cardinale's study, which appears in the April 7 issue of Nature, was funded by the National Science Foundation.

The cleansing power of biodiversity
Scientists have long known that ecosystems that have more plant species tend to have a greater capacity to remove pollutants from soil and water than do ecosystems that have fewer species. But, until now, no one knew how or why this is so.

Cardinale's study helps solve this mystery by explaining how biodiversity promotes the self-cleaning power of streams. According to the study, as algae grow in streams and produce more biomass, they incorporate into their bodies some common forms of pollution and thereby remove it from the water. Each species of pollution-removing algae has evolved and adapted to a different set of conditions, and so occupies a unique mini habitat, or niche, within a water body. Therefore, as the number of species of pollution-removing algae increases in a stream, so too does the number of unique niches that are occupied, filtered and cleansed by them. Hence: the more algae species a stream has, the more total pollutants these organisms may remove from the water.

"As the different habitats in a stream are filled by diverse populations of algae, the stream receives more total biofiltration," said Cardinale. "It's as if the algae work as a better sponge."

"Algae are the sort of thing that are easily overlooked, however Cardinale provides an elegant experiment that shows how the biological diversity of algal species greatly increases the removal of one of the most deadly and insidious toxins in our streams, lakes and rivers," said George W. Gilchrist, a program director in NSF's Division of Environmental Biology.

The process by which species evolve to inhabit their own, unique habitats is known as niche partitioning. "People as far back as Darwin have argued that species should have unique niches, and as a result, we should see a division of labor in the environment," Cardinale said. "But demonstrating that directly has proven very difficult."

The varied types of habitats that may exist within any particular stream include, for example, areas where water flows swiftly vs. areas where water flows slowly.

Study design
Cardinale began his study by growing from one to eight species of algae that are common to North America in each of 150 miniature model streams; each model stream was designed to mimic the varied flow conditions that exist in natural streams, including those dominated by riffles, runs, or calm pools. He then measured the ability of each algal community to soak up a nitrogen compound called nitrate. Cardinale chose nitrates to represent pollution in the study because excess nitrogen is the most common pollutant and the leading cause of degraded water quality worldwide.

Nitrogen is a nutrient found in all living organisms. But excess nitrogen is a pollutant that is usually carried to water bodies in runoff containing nitrogen-based fertilizers and nitrogen-bearing sewage.

Various species of algae were chosen to represent biodiversity in the study because algae are the primary organisms that take up excess nutrients, such as nitrogen, from streams, lakes and oceans.

The power of niche partitioning
Cardinale's results showed that nitrate uptake in the model streams increased linearly with species diversity. On average, the eight-species mix removed nitrate 4.5 times faster than did a single species grown alone.

Evidence that these results were produced by niche partitioning includes the domination of differently shaped forms of algae in different types of stream habitats, as predicted by ecological theory. For example, high velocity habitats were dominated by small, single-celled species of algae that grew in ways that were resistant to displacement by the force of fast-moving water. By contrast, low velocity habitats were dominated by large, filamentous algae that were vulnerable to such forces.

In addition, as part of the research, streams were experimentally simplified until they contained just one type of a habitat, and no opportunity for species to express their niches. Results showed that each of these simplified water bodies then collapsed to one dominant species that singularly drove all nitrate uptake, without species diversity influencing such uptake. These result confirmed that niche differences among species provided the mechanism for biodiversity's cleansing ability.

"One of the primary contributions of this study," said Cardinale, "is that I was able to show exactly why streams that have more species are better at removing these nutrient pollutants from the water. It's just one study, but it's part of a growing body of scientific evidence that is now clearly showing that the modern mass extinction of species is going to affect humanity in some big, and important ways."

Implications of study
Cardinale continues, "One of the obvious implications of the study is that if we want to enhance water quality in large bodies of water, like the Chesapeake Bay watershed or around the Great Lakes, then the conservation of natural biodiversity in our streams would offer, among other benefits, help in cleaning them up."

Nevertheless, scientists are currently warning that accelerating species loses may ultimately lead to a mass extinction comparable in magnitude to that which wiped out the dinosaurs--a possibility that certainly threatens the biodiversity of rivers, streams and other water bodies.

Tuesday, February 22, 2011

The Fire & the Tortoise

Fire maintained ecosystems are often found in geographic regions with Mediterranean climates - southern California, southwest Australia, and of course the Mediterranean. Burning vegetation is an inconvenience, and even prescribed burns are often objected to by local citizens. But, burning-off left-over agricultural biomass has increased in many places. Suppressing fires can lead to the build-up of fuel -dead, dry vegetation- in fire maintained ecosystems and result in increased hazards to both humans and wildlife. How wildlife populations deal with fire is of interest for understanding adaptations to fire and for conservation. Ana Sanz-Aguilar and colleagues have examined how the Iberian Spur-thighed Tortoise, Testudo gracea ibera, manges to coexist with fire at the Cumbres de la Galera Biological Reserve in the Sierra de la Carrasquilla, in Spain. Their study area supported a high density population (about 20 tortoises per hectare) of Spur-thighed Tortoise and they estimated tortoise populations in areas that had frequent fires and areas that had not been burned. The Spur-thighed Tortoise is a long-lived species of the Mediterranean shrublands and the tortoises spend much of their lives sheltered under the vegetation or underground in burrows. These tortoises also bury themselves for hibernate and aestivate, so that they are protected from extreme temperatures, predators and possibly from fires. They found fire caused direct and delayed reductions in local survival, with young individuals being the most affected. Fire-related mortality was highest in juveniles and subadults than adults; this seemed to be related to differences in burrowing behavior. Summer fires had a lesser impact on adults because they spend summer and winter underground in burrows or by burying themselves to avoid temperature extremes. Juveniles and subadults tend to use more superficial burrows or take cover under the vegetation only a few centimeters in depth, thus and are exposed to higher temperature and smoke. The study areas that had fire frequencies similar to those occurring in areas uncontrolled for burns (less than one fire every 20–30 years) tortoise populations were able buffer the effects of fires. But, when fire frequency increased the probability of extinction dramatically increased, except for the largest populations. Thus, T. graeca is able to cope with natural fire frequencies, but the effects of more recurrent fires may severely threaten the species.

Citation:Sanz-Aguilar, A., J. D. Anadon, A. Gimenez, R. Ballestar, E. Gracia, and D. Oro.. 2011. Coexisting with fire: The case of the terrestrial tortoise Testudo graeca in mediterranean shrublands. Biological Conservation (2011), doi:10.1016/j.biocon.2010.12.023

Tuesday, December 14, 2010


Pseudoboa neuweiidi, Trinidad, JCM
 There are six species of snakes in the genus Pseudoboa, all occur in South America, with one species, Pseudoboa neuweiidi, extending its range into the Lesser Antilles (Trinidad, Tobago, Grenada) and possibly into Panama. Pseudoboa coronata (the type species of the genus) and P. neuwiedii occur throughout the Amazon basin. Pseudoboa haasi and P. serrana are endemic to the southeastern and southern regions of the Atlantic rainforest respectively. Pseudoboa nigra occurs throughout the Caatinga, Cerrado, and Chaco biomes in Bolivia, Paraguay, and possibly Argentina. And, the most recently described species, Pseudoboa martinsi (Zaher et al. 2008), is from the Brazilian Amazon basin in the states of Pará, Amazonas, Roraima, and Rondônia. Recent molecular (Vidal et al. 2010) work places these snakes in the family Dipisididae, subfamily Xenodontinae, tribe Pseudoboini. The tribe also includes the genera Boiruna, Clelia, Drepanoides, Mussurana, Phimophis Oxyrhopus, Siphlophis, and Hydrodynastes. All of these are rear-fanged, venomous, and tend to feed on squamates and most of them show interesting ontogenetic color changes with the smaller individuals being more brightly colored or having more contrasting patterns, presumably the coloration and pattern are aposematic.  Hydrodynastes may be the exception to most of these generalizations. Additionally many of these snakes have a nape marking that is collar-like that may last into adulthood. 

Recently, Orofino et al (2010) have reported on the natural history of Pseudoboa nigra using 147 museum specimens. That had been collected in Brazil’s Cerrado mostly from the states Sao Paulo and Mato Grosso. Females were found to be larger than males, the presence of eggs and neonates throughout the year suggests year round reproduction, and they suggest nigra has smaller clutches than other species in the genus. They found it feeds mostly on lizards, Ameiva were the most commonly found food. While the authors suggest that nigra is found in open habitats and other members of the genus are found in more forested environments, my experience with neuwiedii suggests it occurs in a variety of habitats including savanna, coastal, and semi-urbanized habitats that are open (Murphy 1997). While P. nigra may be uniform black in color, it can also have white, irregular blotches that could be considered aposematic coloration. Robert Mertens (1956) considered Pseudoboa a model for more palatable mimics in his proposed mimicry complex hypothesis that eventually became known as Mertens mimicry. To be sure the venom of Pseudoboa neuwiedii is quite toxic, being reported to kill cats, as well as conspecifics (Murphy, 1997). The fact that so many of these snakes are red or orange with a dark collar may mean they are all part of a mimicry complex that use the pattern to remind predators that the head is the business end of the snake. And, because the aposematic coloration is most often found in small individuals and usually not large adults, the warning message may be directed at smaller predators not capable of dealing with a larger snake.

Mertens R. 1956. Das Problem der Mimikry bei Korallenschlangen. Zool. Jahrb. Syst. 84:541–575.

Morato, S. A. A., J. C. de Moura-Leite, A. L. C. Prudenete and R. S. Bernils. 1995. A new species of Pseudoboa Schneider, 1801 from southeastern Brazil (Serpentes: Colubridae: Xenodontinae: Pseudoboini). Biociências 3 (2):253-264.

Murphy, J. C. 1997. Amphibians and Reptiles of Trinidad and Tobago. Malabar: Krieger Publishing.
Orofino, R. de P., L. Pizzatto, and O, A. V. Marques. 2010. Reproductive biology and food habits of Pseudoboa nigra (Serpentes Dipsididae) from the Brazilian Cerrado.  Phylomedusa 9:53-61.

Vidal, N., M. Dewynte,r and D. J. Gower. 2010. Dissecting the major American snake radiation: A molecular phylogeny of the Dipsadidae Bonaparte (Serpentes, Caenophidia). Comptes Rendus Biologies, 333:48-55

Zaher, H.; Oliveira, M.E. & Franco, F.L. 2008. A new, brightly colored species of Pseudoboa Schneider, 1801 from the Amazon Basin (Serpentes, Xenodontinae). Zootaxa 1674: 27-37