Showing posts with label extinctions. Show all posts
Showing posts with label extinctions. Show all posts

Tuesday, November 10, 2015

Culling Koalas for Conservation

Guest post by Stefanie Thibert, who is currently enrolled in the Professional Masters of Environmental Science program at the University of Toronto-Scarborough


Euthanizing diseased koalas may be the most effective management strategy to save koalas from extinction in Queensland. A recent study published in the Journal of Wildlife Disease suggests that if 10% of terminally diseased and sterile koalas were culled while other infected koalas were treated with antibiotics, chlamydial infections could be completely eliminated and population sizes could increase within four years. 
The beloved koala relaxing in a eucalyptus tree
(Source:
http://www.onekind.org/be_inspired/animals_a_z/koala/) 

Although koalas are under pressure from habitat degradation, dog attacks and road accidents, disease burden is the largest threat to its population sizes. It is estimated that 50% of the current koala population in South-East Queensland is infected with the Chlamydia spp. The sexually transmitted disease causes lesions in the genitals and eyes, leading to blindness, infertility, and ultimately death. Rhodes et al. (2011) suggest that reversing the observed population decline in Queensland koalas would require either entirely eliminating deaths from cars and dogs, complete reforestation, or reducing deaths caused by Chlamydia by 60%. It is clear that the best conservation tool is to reduce the prevalence of chlamydial infection.

In the study, Wilson et al. (2015) examined the potential impact of euthanizing koalas infected with Chlamydia. As shown in Figure 1, computer simulation models were used to project koala population sizes based on four separate intervention programs: “no intervention”, “cull only”, “treat only”, and “cull or treat”. In the “cull or treat” program, sterile and terminal koalas were euthanized, while infected kolas that were not sterile or terminal were treated with antibiotics. It was concluded that the “cull or treat” is the most successful intervention program for increasing long-term population growth and eliminating chlamydial infections. 
The projected numbers of koalas in the Queensland population under different intervention programs.(From Wilson et al. 2015)
Without intervention, it is estimated that merely 185 koalas will persist in 2030. Under both the “cull only” and “treat only” intervention, it would take seven years before there would be greater koalas numbers than there would be without intervention. Under the “cull or treat” program, the population size was projected to overtake the no-intervention population after four short years. The population size in 2030 is also greatest under the “cull or treat” intervention. The increase in koala numbers in the “cull or treat” strategy is due to the considerable decrease in the prevalence of Chlamydia.
As expected, the proposal received considerable attention and was scrutinized by the public. Some argue that it is inhumane, while others suggest alternative management strategies. However, when it comes down to it, the science is clear. Euthanizing can be done in a humane way, and it is the most effective method for conservation of the species. The only real alternative to culling is treatment with antibiotics, which is costly, requires an immense amount of monitoring, and has been shown to take much longer to eliminate the disease and increase population sizes.
The question we must ask ourselves is: we cull other species, so why not koalas? For instance, in the United States, the culling of four million cattle successfully prevented bovine tuberculosis from spreading to humans. Even when based on sound scientific research, culling has always been dismissed as a management option for the iconic Australian marsupial. In 1997, culling was suggested as a method to protect the overabundant koala population on Kangaroo Island, but sterilization and relocation was used instead. It is amazing that a program that was significantly more expensive and less effective was chosen because the public could never think of killing the adorable and innocent koala.
Managing koala populations is clearly a case in which science intersects with emotion. However, it is essential that we put our emotions aside, and make a decision that is based on scientific evidence. Let us remember that the study only suggests culling or treating 10% of the population each year, which is equivalent to approximately 140 koalas. It is also important to improve the communication of science to the public. It needs to be made abundantly clear that without culling, the koala populations will continue to decrease.


To read the full article visit: http://www.bioone.org/doi/full/10.7589/2014-12-278 

References:

Oliver, M. (2015, October, 20). Proposal to euthanise koalas with chlamydia divides experts. The Guardian. Retrieved from: http://www.theguardian.com/world/2015/oct/20/proposal-to-euthanise-koalas-with-chlamydia-divides-experts.

Olmstead, A.L., & Rhode, P.W. (2004). An impossible undertaking: The eradication of bovine tuberculosis in the United States. Journal of Economic History, 64, 734-772.

Rhodes, J.R., Ng, C.F., de Villiers, D.L., Preece, H.J., McAlpine, C.A., & Possingham, H.P. (2011). Using integrated population modeling to quantify the implications of multiple threatening processes for a rapidly declining population. Biological Conservation, 144, 1081–1088.

Wilson, D., Craig, A., Hanger, J., & Timms, P. (2015). The paradox of euthanizing koalas to save populations from elimination. Journal of Wildlife Diseases, 51, 833-842.


Monday, May 11, 2015

Is there a limit to how many species can the earth hold?

Counting species (bird lists, plant guides) is as old as ecology itself. And yet surprisingly, there are still different opinions on how many species the planet holds, and even, whether there are limits on how many species it can have. If the number of species has ecological limits, the assumptions ecologists often make – that species pools are limited and knowable, dynamics can reach equilibrium, competition should usually be important – would be stronger. Things would be more predictable. 

But is the production of diversity self-limited? There isn’t consensus but two recent articles in the American Naturalist (continuing a debate at the American Society of Naturalists meeting) provide some excellent debate of this question.

The debate is whether the majority of variation in continental-scale species richness is regulated by diversity-dependent feedbacks. In these papers, Dan Rabosky and Allen Hurlburt argue that species richness has ecological limits, while Luke Harmon and Susan Harrison take the contrary position, that species richness is dynamic. First, to define some terms: here, species richness is being considered at the largest spatial scale (e.g. terrestrial plants at the continental scale) so that dispersal limitation should be comparatively unimportant (because diversity changes are mostly driven by in situ speciation).

The crux of the Rabosky & Hurlburt argument is established in the Ecological Limits Hypothesis (ELH), which states that species richness will reach a dynamic (i.e. stochastic) equilibrium, where equilibrium richness reflects density dependence in speciation and/or extinction rates. Speciation and extinction rates are ultimately limited by total resource availability for the continent. Therefore variance in richness through time and between places should be driven these ecological limits, and richness should be predictable.
From Rabosky & Hurlburt 2015 - the Ecological Limit Hypothesis.
The evidence presented for the ELH comes from phylogenies and macroevolutionary models, the fossil record, and macroecological observations. First, there are well known patterns between species richness and energy, productivity, or habitat area, and these span multiple regions and groups of species (e.g. Jetz and Fine 2012). Further, Rabosky & Hurlburt argue that geological records suggest that changes in diversity are not unbounded or exponential, but instead rise and fall, correcting toward some equilibrium. Molecular phylogenies are often evaluated by looking at speciation rates over time, and the authors suggest that these frequently show declines, where speciation declines during adaptive radiations. One prediction that arises from the ELH is that perturbations will be followed by particular responses: “negative perturbations—mass extinctions, in particular—should lead to diversity recoveries. Second, positive perturbations—increases in the resource base available to a biota—predict increases in species richness to stable but greater equilibrial levels”.

The rebuttal article from Harmon & Harrison takes a strong and contrasting view, although it focuses mostly on poking holes into Rabosky & Hurlburt’s arguments, rather than laying out a competing hypothesis. If Rabosky & Hurlburt focused on evidence over huge evolutionary scales and spatial expanses, the Harmon & Harrison response has a particular interest in the temporal and spatial scales of interest to community ecologists (local, present day) and how these seem to disagree with Rabosky & Hurlburt's hypothesis.

First, Harmon & Harrison argue that that the macroevolutionary evidence (molecular phylogenies, fossil data) is not nearly so convincing as Rabosky & Hurlburt suggest. There are important limits to its utility resulting from issues of ambiguity in interpretation and methodological limitations. In addition, for most of the patterns Rabosky & Hurlburt highlight, there are other papers concluding that the pattern was not present in their data. With reference to the lack of relationship between clade age and diversity: “A common interpretation of these results is that a lack of a relationship between age and diversity is evidence for ecological limits.... However… this pattern is far from ubiquitous in real data and is compatible with other explanations”. They also take issue with the tendency for hand-wave-y interpretations of patterns in such data, and emphasize the need for better statistical analyses and consideration of alternate models. Fossil data has obvious limitations as well (hence the field of taphonomy), including the fact that fossils are rarely classified to the species-level, which means they do not represent species richness, but rather lineage richness.

But Harmon & Harrison's real disagreement is based on their view that ecological evidence from local communities does not at all suggest ecological limits. Energy-richness correlations, although common, may have alternative explanations: the tropics may have higher diversification rates for other reasons, or niche conservation means that more species niches suited to the tropics, confounding energy-diversity relationships. Further, local communities do not regularly show a positive energy-diversity relationship. In particular, Harmon & Harrison suggest that the logic from the ELH, if followed, predicts that if species richness is ultimately tied to the availability of energy, then competition should necessarily be very important in most ecological communities. They cite a stat from the invasion of California flora in which alpha diversity has risen by more than 1000 invasive species, with only 28 native extinctions (as of 2002), suggesting that local (or even regional) communities are not full. 

To this, Rabosky & Hurlburt rejoins that invasion is about dispersal changes, and not resources. Further, they believe that large evolutionary scales are most useful as evidence for the ELH, since they are most likely to show zero sum game, rather than temporary dynamics, and since confounding factors should become minimized.

The debate left me feeling a little unsatisfied (since expecting the authors solve the problem is a bit unreasonable), in part because the authors are really arguing from different scales and approaches. And both sides are clearly right in some cases (and in others, perhaps, clearly overreaching). And of course, proving whether or not there is an ecological limit on diversity is a rather difficult thing. When Harmon and Harrison argue that the ELH, which assumes that richness approaches some equilibrium value but varies about it in a stochastic fashion, isn’t parsimonious, they’re wrong – ecological processes are innately stochastic and it hardly seem un-parsimonious to assume as much. But they’re right that this view makes testing and model fitting very difficult since having high replication and good quality data is necessary (to capture accurately a distribution, rather than single value). Given the variety of issues with data representing diversification over evolutionary time, and frequently an inability to capture extinction rates with evolutionary data, having quality, replicated tests of the ELH is difficult.

On the other hand, at local scales over ecological time, observations may be less relevant. It’s not clear how to reconcile statements about saturation (or lack thereof) of local communities with richness at continental scales. Rabosky & Hurlburt suggest that local assemblages can be dynamic in diversity as long as there is a zero sum across all communities and through time. But a connection between continental scales and local scales is innate, and understanding how diversity relates over multiple spatial scales is an area of ecological research we need to continue to develop.

Given there are no easy tests of this sort of question (though bacterial microcosm provide some interesting results), we have been forced to draw conclusions based on weak tests and weak evidence. But ecologists do this because this is a truly important question, with huge implications across ecology and evolution. Ecological and evolutionary models make assumptions that implicitly or explicitly about carrying capacity, about determinants of rates of speciation and extinction, about invasion, about why global diversity changes, and these need to be confirmed. Further, if there is a strong ecological feedback of diversity, one of the most important implications is that major perturbations such as extinctions should be followed by major recoveries. In the Anthropocene, that’s an important implication. 

Monday, November 17, 2014

Northern White Rhinoceros – On the Brink of Extinction

*Guest post by Monica Choy -one of several posts selected from the graduate EES3001 Scientific Literacy course at University of Toronto-Scarborough.

Photo credit: Elodie A. Sampere, Getty Images
Suni, a 34 year old male northern white rhinoceros, died on October 17, 2014 of natural causes. His death reduced the total number of known northern white rhinos to an alarming six individuals, which has brought his species one step closer to extinction.1

Suni was born in a zoo in the Czech Republic and was the first of his kind to be born in captivity. Unfortunately, northern rhinos are a finicky species when it comes to breeding and with increasing pressures from poaching, it became critical to provide the animals with a natural, comfortable space.

As a result in 2009, Suni and three others were transported to the Ol Pejeta Conservancy in East Africa.  It was believed this change in scenery would most accurately imitate their natural environment.2 Rhino conservationists anticipated that the rhinos would then breed naturally and provide a healthy calf that would bring new hope for the waning species.

Even before these desperate attempts to keep the species going however, the history of the northern rhino has been a sad one. At the time of Suni’s birth, his species was on a very slow rebound. Northern white rhinos had been excessively poached for their horns, and their initial population of over 2,000 animals declined to a shocking 15 rhinos by the late ’80s. Conservation efforts were ramped up in the ’90s and it looked as though the animals were making a gradual comeback. Unbelievably, poachers also increased their efforts and knocked the numbers back down to below 10 individuals by the mid-2000s.3

Northern white rhinos were declared extinct in the wild by 2008.

The likelihood that Suni’s species will become extinct in our lifetime has increased significantly with his death. And although the Ol Pejeta Conservancy will continue trying until the bitter end with the use of techniques such as artificial insemination, the precarious position the northern white rhino is in, as stated in their press release, is “a sorry testament to the greed of the human race.” 1

The extinction of such a charismatic species is a tragedy and should bring awareness to how heavily humans really affect our environments. Although the northern white rhino may be on the brink of extinction, there are still a countless number of other species out there that need our help. It is up to us to work together in order to keep other species as far from the fate of the northern rhino as possible.


More information
1Ol Pejeta Conservancy press release  - http://www.olpejetaconservancy.org/about/news/breaking-news-ol-pejeta-conservancy-loses-one-its-northern-white-rhinos
2Northern white rhino conservation project - http://www.olpejetaconservancy.org/sites/default/files/NWR_FAQ_FINAL.pdf

3WWF profile of the northern white rhinoceros - http://wwf.panda.org/what_we_do/endangered_species/rhinoceros/african_rhinos/white_rhinoceros/

Tuesday, December 3, 2013

Biodiversity hotspots: are we missing other priorities?

ResearchBlogging.orgBiodiversity hotspots are regions that harbour disproportionate biodiversity, especially of species with small ranges, and regarded as major conservation priorities (Zachos and Habel 2011). Biodiversity hotspots occur in some of the most exotic and romanticized regions around the world, such as Madagascar, the Caribbean Islands, the Western Ghats of India, and the Succulent Karoo of South Africa. By preserving these regions, we disproportionately preserve the diversity of life on Earth, and thus these conservation efforts are seen as critically important.

However, some argue that the emphasis on global biodiversity hotspots leaves other unique or less diverse regions open to human impacts since they have a perceived low natural value, and certainly not valuable enough to stem other economically motivated activities. This mind set may put large habitats under increased risk. This conflict is front and center in a recent paper by Durant and colleagues in Diversity and Distributions (Durant et al. 2013). In this paper, Durant et al. argue that large, globally relevant systems like hot deserts are under-protected, leading to potentially major collapses in these systems.

Ahaggar Mountains Oasis, from Wikipedia

They use the Sahara desert as the case study and show that while conservation efforts have been focused on hotspots, the majority of large vertebrates in the Sahara desert are now extinct or critically endangered.  System like hot deserts are important for human economic well-being, but our activities there have greatly reduced the amount of intact, undisturbed habitat.

Durant et al. argue, that had there been greater conservation effort and scientific interest in the Sahara, the catastrophic declines in large vertebrates may have been averted. This paper highlights the reality that we often undervalue certain ecosystems, regardless of the important ecosystem services and functions that they deliver.

S. M. Durant, T. Wacher, S. Bashir, R. Woodroffe, P. De Ornellas, C. Ransom, J. Newby, T. Abáigar, M. Abdelgadir, H. El Alqamy, J. Baillie, M. Beddiaf, F. Belbachir, A. Belbachir-Bazi, A. A. Berbash, N. E. Bemadjim, R. Beudels-Jamar, L. Boitani, C. Breit (2013). Fiddling in biodiversity hotspots while deserts burn? Collapse of the Sahara's megafauna
 Diversity and Distributions DOI: 10.1111/ddi.12157





Friday, April 5, 2013

Measuring the Pacific extinction spasm


ResearchBlogging.orgIt is a fact that humans have caused numerous extinctions around the globe. Almost all of the large bodied mammals of North America disappeared after the arrival of humans sometime around 20,000 years ago –likely due to compounding effects of hunting and climate change.  This North American example has been controversial, largely because it constitutes a single observation. However, humans colonized the Pacific islands over a span of a couple of thousand years, between 3,500 to 700 years ago. Species extinctions followed these colonizations on each island, confirming the link between humans and extinctions. Yet how many species went extinct? This question may be relatively easily answered for large organisms since evidence of their existence is well recorded, but for small-bodied organisms like birds, this is a difficult question to answer.


In a recent paper in the Proceedings of the National Academy of Sciences, Richard Duncan, Alison Boyer and Tim Blackburn use sophisticated methods to estimate the true magnitude of bird (specifically nonpasserines –i.e., not perching or songbirds) extinctions on 41 Pacific islands (including islands from Hawaii, Melanesia, Micronesia and Polynesia). Estimating the number of extinctions prior to recorded history is an extremely difficult exercise, but Duncan and colleagues use a set of statistical methods (Bayesian mark-recapture) to produce reliable estimates. The data available include a spotty fossil record, and so the researchers needed an appropriate estimate of the number of species present on islands in the past. To do this they examined the fossil record and compared it to species that are found there today. Only a subset was found in the fossil record. From this, they determined how the number of fossils found, body size of the organisms and island size affected detection probability. With these informative detection probabilities, they were able to estimate past richness and compare that to today’s richness – and the difference is the number of extinctions.

Across these 41 islands, Duncan et al. estimate that human colonization resulted in at least 983 extinctions. Nine-hundred and eighty-three species are no longer with us because of the presence of humans. Coupled with human activities elsewhere, from over-hunting, habitat destruction and the introduction of non-native species, we responsible for thousands of extinctions. For the first time in Earth’s history, a single species (us) is the direct cause for thousands of other species going extinct. A paper such as this is an important analysis, but it certainly doesn’t make us feel good about ourselves.

Duncan, R., Boyer, A., & Blackburn, T. (2013). Magnitude and variation of prehistoric bird extinctions in the Pacific Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1216511110

Monday, March 18, 2013

Evolution on an ecological scale


Andrew Gonzalez, Ophélie Ronce, Regis Ferriere, and Michael E. Hochberg. 2013. Evolutionary rescue: an emerging focus at the intersection between ecology and evolution. Philos Trans R Soc Lond B Biol Sci. 368 (1610).doi: 10.1098/rstb.2012.0404 (Intro to special issue).

David A. Vasseur, Priyanga Amarasekare, Volker H. W. Rudolf, Jonathan M. Levine. 2011. Eco-Evolutionary Dynamics Enable Coexistence via Neighbor-Dependent Selection. The American Naturalist, Vol. 178, No. 5, pp.E96-E109.

Ecology and evolution are often treated as connected but ultimately discrete areas of study. Ecological processes are usually the main source of explanation for ecological patterns and  ecologists may ignore evolutionary processes under the assumption that these are most important over longer time scales than are of interest (e.g. speciation). However, there is also an increasing recognition that rapid evolutionary dynamics can contribute to ecological observations. In a time where rapid changes to climate and habitat are the greatest threats to most species, the suggestion that rapid evolution might play a role in extinction prevention and diversity maintenance is an important one.

Increasingly researchers are exploring this concept. The concept of evolutionary rescue (ER), has been particularly championed by Andy Gonzalez and Graham Bell of McGill University. ER results when evolution occurs fast enough to arrest population declines and allow populations to avoid extinction in the face of changing conditions. Changing conditions resulting in maladapted populations should result in population declines followed by extinction. However, if selection for resistant types (which are present in the population, or result from mutations) occurs, population declines can be countered. The result is a characteristic u-shape curve, showing the initial geometric decline, followed by a geometric increase – escape from extinction is then a balance between rates of evolution and success of resistant types compared to rates of population decline.
From Bell & Gonzalez 2009.
The question of whether evolution may have relevance to population declines is not precisely new, but it is especially relevant given we are in a period of habitat changes and extinction. A special issue of Proc B is focused only ER, on the question of its importance, prevalence, and predictability. Many of the articles extend theory, exploring assumptions about the type of environmental change, type and extent of the threat, presence of dispersal, spatial gradients, etc. A few articles attempt the more difficult task of testing for ER in natural systems and assessing its likely prevalence and value to conservation activities. It is an interesting journal issue and a great example of the importance of context in determining when an idea takes off. The theoretical background for evolutionary rescue has existed for many years, but it took the context of climate change (and perhaps the collaboration of an ecologist and evolutionary biologist?) for it to gain ground as an area of ecological research.

Another interesting paper, this one linking evolutionary dynamics with community coexistence, is from Vasseur et al. (2011). In this case, the authors suggest an evolutionary mechanism that could augment coexistence when ecological conditions allow for niche partitioning and that could allow coexistence when ecological conditions lead to competitive exclusion. If species exhibit tradeoffs between traits that are optimal for intraspecific interactions and traits that are optimal for interspecific interactions, evo-ecological dynamics can produce coexistence. Such tradeoff means that a species will be a superior interspecific competitor when rare and a poor interspecific competitor when common. Such a tradeoff creates neatly alternately selective pressures depending on whether a species is common (fitness declines) or rare (fitness increases). This is presented as a theoretical model, but it seems like in a tractable system one could easily test for changes in ecological and evolutionary pressures as predicted by the model.

No one would argue with the conclusion that a closer relationship between ecology and evolutionary biology would be beneficial for both. But in practice this seems to be the exception rather than the rule. "Evolutionary ecology" as it exists is fairly restricted, and if complaints about seminar topics is to provide a hint, most ecologists feel disconnected from evolutionary topics and vice versa. If evolutionary dynamics are relevant on an ecological scale, it seems that we should at least attempt to understand their prevalence and importance in natural systems.