Archive for: January, 2010

Climate change, invasives and extinction in Thoreau's Woods

...I walk encouraged between the tufts of Purple Wood-Grass, over the sandy fields, and along the edge of the Shrub-Oaks, glad to recognize these simple contemporaries. With thoughts cutting a broad swathe I “get” them, with horse-raking thoughts I gather them into windrows. The fine-eared poet may hear the whetting of my scythe. These two were almost the first grasses that I learned to distinguish, for I had not known by how many friends I was surrounded — I had seen them simply as grasses standing. 

From "Autumnal Tints" by Henry David Thoreau The Atlantic Monthly October 1862. In this photo from 1908, the rocks mark the location of his cabin in relation to Walden Pond.

ResearchBlogging.orgAround 1851, after completing the retreat that inspired Walden, Thoreau had taken his interest in nature and made it a more scientific part of his work routine, walking the woods and fields around Concord, Massachusetts recording his observations of plants and animals through the seasons in the area. He paid particularly close attention to the flowering days of local plants, which has been of interest to the scientific community of late.

The data that Thoreau collected is meticulous enough to be considered a viable, useful data source by modern researchers. Thoreau's records of the area's wildlife have been carried on by others, providing us with over 150 years of data regarding the phenology of Northeast American flora; that is, life cycle events like fruiting or flowering days or migration and how these events are influenced by the seasons and the climate. Simply put, after 150 years of suffering the effects of disturbance and climate change, the natural communities of Concord are not quite the forests and fields of yore.

In the past two years or so there have been a handful of studies based on the data set that Thoreau started. In February 2008, Rushing and Primack published a study in Ecology discussing how global warming had affected flowering times in Concord. The average temperature has increased in the area by approximately 2.4° C since 1852, which has, on average, pushed flowering times up by 7 days since Thoreau's time. It was also observed that two non-native plants common in the Northeast, St. John’s wort (Hypericum perforatum) and highbush blueberry (Vaccinium corymbosum), could be useful as bioindicators of the future effects of climate change due to how quickly they responded to the changing temperatures; their mean first flowering days shifted forward approximately three days per 1° C increase in temperature.*

Later that year, Willis et al. published a study in PNAS using the data set started by Thoreau, this time looking at the data from a phylogenetic perspective. It was shown that flowering time was strongly correlated with abundance and that the species seemingly incapable of a relatively quick response to the change in climate were declining. The pattern is phylogenetically selective, strong evidence of climate change as an extinction risk.

In the near term, this pattern of phylogenetic selectivity is likely to have an accelerated impact on the loss of species diversity: groups of closely related species are being selectively trimmed from the Tree of Life, rather than individual species being randomly pruned from its tips.

A more recent study from Willis and his colleagues published in PLoSONE takes a look at how these flowering times differ between native and non-native species, determining how each has been able to respond over the past 150 years. It was previously demonstrated that the non-natives St. John's wort and highbush blueberry have been apt conformers to the changing climate, but neither are considered invasive.

The researchers placed the Concord flora in four comparative categories for analysis - Native vs. non-native, Native vs. non-native, non-invasive, Native vs. invasive, Non-native, non-invasive vs. invasive - and examined phenologically and ecologically important traits such as plant weight at maturity and flower diameter.

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The results are remarkable, and reveal another layer of danger to native plants in the area. In general, non-natives were shown to adapt to changing temperatures better than the natives. Invasive species are particularly apt; they flower 11 days earlier than natives and 9 days earlier than the non-native, non-invasives. The results of the study also backed up earlier evidence that abundance was tied to earlier flowering days; invasives displayed greater relative abundance than the natives and non-native, non-invasives. But in general, non-natives in the area are equipped with certain traits that better prepare them for changes in climate.

Already the Concord area has lost about 27 percent of the species that once inhabited Thoreau's woods and another 36 percent have become incredibly rare. If the projections of 1.1° - 6.4° C increases in average temperature over the next century are correct, this trend will continue, progressively selecting traits that promote invasive growth and pushing natives that much closer to extinction.

*It's not always a boon for the flowering days of plants to be pushed forward in the season. If flowering too early, they may miss their pollinators or succumb to a late frost.

Willis, C., Ruhfel, B., Primack, R., Miller-Rushing, A., Losos, J., & Davis, C. (2010). Favorable Climate Change Response Explains Non-Native Species' Success in Thoreau's Woods PLoS ONE, 5 (1) DOI: 10.1371/journal.pone.0008878

Willis CG, Ruhfel B, Primack RB, Miller-Rushing AJ, & Davis CC (2008). Phylogenetic patterns of species loss in Thoreau's woods are driven by climate change. Proceedings of the National Academy of Sciences of the United States of America, 105 (44), 17029-33 PMID: 18955707

Miller-Rushing AJ, & Primack RB (2008). Global warming and flowering times in Thoreau's Concord: a community perspective. Ecology, 89 (2), 332-41 PMID: 18409423

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>Climate change drying up streams, reducing the reproductive success of bats in the Rockies

Jan 28 2010 Published by under Animals, Conservation, Ecology, Environment, Research Blogging

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Bats
From left to right: fringed myotis (Myotis thysanodes), the big brown bat (Eptesicus fuscus) and the long-eared myotis (Myotis evotis).

ResearchBlogging.orgWith the widespread effects of the changing climate on biological communities and landscapes across the world, it has become increasingly important for ecologists to identify indicator species among these ecosystems that can indirectly relate information about environmental changes that are not apparent or easily accessible. So it is in the west, the Rocky Mountains and in particular the Colorado River Basin, where temperatures have increased more than anywhere else in the contiguous United States, an average 1.2° C higher than the 20th century averages. The biggest increases in temperature happens at the highest elevations, which is

With warming temperatures comes less precipitation and less snowpack, which means during the summer months, the breeding season for most species, there is significant reductions of stream discharge, which has reduced the flow of the Colorado River. Thirty million people rely on the water provided by the Colorado River, and the Basin is foundational to all life in such a dry environment. Bats, as this article in Ecology explains, are particularly sensitive to these changes and, due to their enormous numbers, are integral to food webs as predator and prey. They may be that indicator ecologists are looking for.

Using capture and environmental data from over 12 years - 1996 to 2008 - Rick Adams from the University of Colorado has demonstrated dramatic correlations between the reduced availability of water and declines in the reproductive success of certain species of bats in the west. Bats are particularly sensitive to evaporative loss because of their small size, large surface area to volume ratio and uninsulated wings. Reproductive females are particularly sensitive considering that 76 percent of their milk is water. Lactating fringed myotis bats have been demonstrated to drink 13 times more often than non-reproductive females from nearby sources like streams or pools.

The study area was in the foothills of the Rockies, between 1650 m and 2250 m, a mix of montane meadows, shrubland, pine woods, riparian woodland and mixed coniferous forest, the habitats of nine species of bats; data was collected on the five most common: small-footed myotis (M. ciliolabrum), little brown myotis (Myotis lucifugus), big brown bat (Eptesicus fuscus), long-eared myotis (M. evotis), and fringed myotis (M. thysanodes). The 2,329 bats captured were put into one of four categories: Non-reproductive, Pregnant, Lactating or Post-lactating.

The reproductive output of these bats has declined, especially when stream discharge dipped below 7 cubic meters per second. During the hottest and driest years, 2007 and 2008, Adams captured more non-reproductive females. Among two species, M. thysanodes and M. lucifugus, the percentage of non-reproductive females was remarkably high, 56 percent and 64 percent respectively.

Both of these species use maternity sites having south or southeast aspects that promote highest solar gains throughout the diurnal roosting period (Adams and Thibault 2006; Adams and Hayes 2008), maintaining internal temperatures between 27° C and 36° C (Adams unpubl. data). Such microenvironmental conditions within roost sites promote high evaporative water loss and consequently a greater need for water intake, especially during the lactation period.

The other myotis species are more likely to roost in cooler, more humid microclimes, closer to the ground.

So if bats - mammals with high mobility* - are facing difficulties from a reduction of water availability, what about other animals more restricted to certain areas? How is this aspect of climate change affecting them? Bats, Adams says, are good bioindicators, organisms that can help scientists predict similar, indirect effects of climate change in other regional animal populations.

Current predictions from the IPCC tell us that this is just the beginning; it's "very likely" (90 percent confidence) that ecosystems will be significantly affected if the warming trend continues. In the next century, due to continued average temperature increases and an increase in the frequency of heat waves and drought, the Colorado River is facing a potential 8 - 11 percent reduction of flow. This will certainly exacerbate the bats' reproductive problems, but perhaps the continuance will afford ecologists the opportunity to transpose data to study similar problems among other animals and propose meaningful, sensible solutions - even if they are bandaids, like providing artificial water sources for vulnerable populations, temporary but viable, buying much needed time for more comprehensive applications.

*Bats are mobile, but they stick to their traditional maternity sites, still focused in a local area.

Adams, R. (2010). BAT REPRODUCTION DECLINES WHEN CONDITIONS MIMIC CLIMATE CHANGE PROJECTIONS FOR WESTERN NORTH AMERICA Ecology DOI: 10.1890/09-0091

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Coastal dune ecology: Invasive grass driving native herb to extinction through direct and apparent competition

Jan 22 2010 Published by under Ecology, Environment, Research Blogging

ResearchBlogging.orgI was reading through this study from Ecology yesterday, which tells the interesting story of how coastal dune ecology in northern California was invaded in the 19th century and subsequently disrupted. In order to stabilize the ever-shifting sand dunes, a grass called Ammophila arenaria, the European beachgrass, was planted along the coastline. A. arenaria grows from a strong, thick network of branching rhizomes, allowing it create a fast hold on loose soil and, as the coastal managers intended, create a framework that slowed erosion.

A. arenaria

Of course, what was preferable to coastal managers wasn't for the native wildlife. A. arenaria has spread all the way up to British Columbia since then, supplanting the native populations and potentially pushing one particular species of plant to extinction in the near future.

Lupinus tidestromii (link to the researchers' project homepage with some great photographs) was flowering on the dunes of northern California long before the European beachgrass arrived. The beachgrass is a direct competitor with L. tidestromii for the basics - sunlight, water and territory - but according to the authors, there are two other ways in which A. arenaria threatens L. tidestromii.

First, A. arenaria has limited L. tidestromii's seed scarification and germination. By anchoring the sand dunes, the invasive beachgrass has greatly reduced the chance for strong winds to remove the top layer of soil and vegetation from the dunes, which can expose and disperse dormant seeds. The researchers believe that L. tidestromii probably thrived when this mode of scarification was more prevalent since its seedlings are usually the first to establish after such "blowouts", but are quickly overtaken by A. arenaria.

Second, there is not only direct competition between the invasive and the native, but also a type of indirect competition called "apparent" competition that is playing a greater role in L. tidestromii's decline. In general, this type of competition revolves around two producers and a shared predator. One producer's population changes, which leads to a change of the predator population and finally, a change in the second producer's population (this is not exclusive to invasive populations, this mechanism applies to native communities as well). In this case, the invader A. arenaria is providing housing for L. tidestromii's main pre-dispersal seed predator, the deer mouse (Peromyscus maniculatus), which is bolstering their numbers and increasing pre-dispersal predation within 100 meters of these refuges. The beachgrass covers large areas of coastal land, giving these animals plenty of places to hide and plenty of opportunities to snatch up seeds en masse before they can be dispersed.

In order to restore L. tidestromii's dwindling population, the beachgrass needs to be removed, which will reduce the area of refuge for the deer mouse, reduce their populations and alleviate some of the pressures on the lupine's seed dispersal. The researchers have already projected an increase in one population of L. tidestromii, from only a marginal reduction in seed predation.

(I tried to keep in mind while reading that this is only two species evaluated regarding an introduced species that affects many other organisms in a wider ecosystem; that the effects are so pervasive in so small an interaction is remarkable.)

The authors believe that apparent competition may be responsible for homogenization and certain cases of selective extinction dependent on predator preference:

When invasive plants compete strongly with native plant communities via apparent competition, native species preferred by consumers are selectively eliminated from the community. As a result, invaded communities will ultimately contain a more homogenous composition plant species that are not preferred by consumers.There are many examples where changes in the abundance of an herbivore or introduction in an exotic herbivore changes plant community composition towards less preferred species. Throughout eastern North America, white-tailed deer have increased in density due to habitat fragmentation, supplemental food sources and the eradication of large carnivores; this in turn causes a reduction in the relative abundance of their preferred plant species (Augustine and McNaughton 1998). In addition, the introduction of exotic cattle to American landscapes similarly shifts plant communities toward those species that are not preferred (Fleischner 1994).

Two of the three populations of L. tidestromii that were analyzed are on a projected decline to extinction. Unless measures are taken to reduce the omnipresent influence of European beachgrass, this unique little lupine may disappear for good.

Dangremond, E., Pardini, E., & Knight, T. (2010). Apparent competition with an invasive plant hastens the extinction of an endangered lupine Ecology DOI: 10.1890/09-0418

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Irreplaceable natural services: A look at the plight of the Chihuahuan grasslands and the black-tailed prairie dog

Jan 14 2010 Published by under Animal, Behavior, Ecology, Environment, Research Blogging

ResearchBlogging.orgI've written in general about grasslands before, as a biome, making sure to note that these treeless plains have always been the stage of expansive growth and decline for both the animal world and the human world, a stage upon which our skill at mastering our environment and bending it to our will is most apparent. Our achievement in converting grasslands from complex ecosystem to agricultural workhorses is only matched by our negligence in understanding how these delicate systems work and the potential danger of reaching a point of no return in grasslands management.

This article from PLoS ONE,  provides a very clear, apt example of just how delicate this biome can be, and illustrates the services that native animals can provide in an ecosystem that would cost considerable sums to replace. Grasslands are rapidly being converted to shrubland and in some cases, bare ground. Agriculture has disturbed a major architect of the grasslands of northwestern Mexico: the black-tailed prairie dog (Cynomys ludovicianus).

These photos show the rapid loss of prairie dogs within the largest colony of the Janos grasslands, following two decades of intensive land use and drought. Note the sparse coverage of annual grasses and forbs and the lack of perennial grasses, which is characteristic of degraded grasslands in Janos. These plants are only available during the rainy season and most of the year the area is bare ground. doi:10.1371/journal.pone.0008562.g002

The 55,000 hectare prairie dog complex (an assemblage of eight colonies) in the grasslands of Janos Valley in Chihuahua was fragmented and reduced by 73 percent from 1988 – 2005. The researchers saw prairie dog densities drop from 25 per ha to a dismal 2 per ha and the average colony size from approximately 6,250 ha to 437 ha (though a couple of larger colonies do still exist). Almost across the board, vertebrates in the grasslands would suffer similar declines in the same time period.

The black tailed prairie dog is a keystone species of the Janos grasslands. It performs a critical role in shaping and maintaining the ecosystem to which it belongs in three ways:

 

  • They are a vital source of food for predators like raptors, owls and coyotes.
  • The burrows they create are used as homes and habitats by other life.
  • They prevent the encroachment of shrubland by eating the seeds and saplings of woody plants like ephedra and mesquite.

The last benefit is perhaps the most significant, at least to shrinking grasslands. The researchers were given unique opportunities to study the extent of this ecological boon, two cases: one where they could see the aftereffects of the removal of a colony and one where they could observe the expansion of one.

In 1988, the Los Ratones colony was poisoned, a colony comprising almost 1,600 ha. In the absence of the prairie dogs, 34 percent of the surrounding grassland was converted to shrubland by 1996. Just to be clear, that is 34 percent is not a percentage of the land that the colony covered, but a percentage of the surrounding grassland, which actually comprised more hectares than the Los Ratones colony itself. Why is that important to mention? The second case neatly dovetails.

The researchers watched the La Bascula colony expand 16 percent into the surrounding ephedra-dominated shrubland over a five year period, between 2000 and 2005. In the area around the colony, 81 percent of the ephedra had signs of 'prairie dog clipping' and, on average, the plants around the colony were 55 percent shorter than the plants on the colony outskirts, of which only 3 percent showed the hallmark of pruning. The prairie dogs had effectively cut a swath of 546 meters into the ephedra, converting a large area into grassland and maintaining it with their mere presence.

So when colonies of black-tailed prairie dogs are fragmented and reduced in size and number, the grassland is missing its most diligent protector, allowing the shrubland to expand. Some species have seemed to move and adapt to the shrubland when the ungrazed grassland habitat became more scarce:

 

...the bunchgrass lizard (Sceloporus scalaris), a species highly associated with perennial grassland habitat, ...was more abundant in the shrublands in our study. This species may have preferred the more structurally complex shrublands compared to the heavily grazed grasslands, as it has been found to be ten-times more abundant in ungrazed perennial grassland than grazed grassland. 

It's not the standard, however. The endangered and threatened species that thrive in the grassland - particularly the carnivores and larger mammals - have seen startling declines.

Mammal and bird species in the Janos prairie dog grasslands showing dramatic declines in densities over time. (Note prairie dog densities are compared from 1994–2004.) Of the 33 bird species that were sampled, only those that exhibited a 2-fold or greater change over time are shown here. doi:10.1371/journal.pone.0008562.g009

I think it's important to mention that this article is not saying 'grassland good, shrubland bad'; it's highlighting how important one species can be to a delicate and anthropogenically overused ecosystem. In fact, the researchers make clear in the article that in general, species richness and diversity was actually higher in the shrublands. But the most threatened species depend on the grassland for their livelihood, which is why it's so important to try to preserve and manage it properly.

It's encouraging to see results. Often the rhetoric from NGOs and activists regarding the morality and practicality of protecting threatened areas starts to blend and lose impact, so it's vital to publicize studies that bring to light exactly the sort of "kick em in the wallet" attention grabbers that legislators need to see.

The researchers are working with ranchers in the area, trying to come up with management solutions instead of just kicking down the door and saying 'no', so to speak. They hope to use the cattle to clear spaces for the prairie dogs to recolonize, reduce the grazing pressure so that the fires can return, which in turn will clear more shrubland, making way for further colonization.

It's realistic, practical solutions like these that will not only protect the ecosystems that are in danger, but also forge new relationships with people a world away from the West. Can we really blame these people for being suspicious of our intentions, for assuming that this is just another mode of control or that we are disregarding their culture yet again, a culture certainly more intact and probably less confused than ours currently?

Ceballos, G., Davidson, A., List, R., Pacheco, J., Manzano-Fischer, P., Santos-Barrera, G., & Cruzado, J. (2010). Rapid Decline of a Grassland System and Its Ecological and Conservation Implications PLoS ONE, 5 (1) DOI: 10.1371/journal.pone.0008562

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