The question of whether dinosaurs were endothermic has been a rich source of controversy for decades. Although they were originally portrayed as sluggish reptiles that crept their “cold-blooded” way through the Mesozoic, over time evidence has suggested that they may have actually had active and athletic lifestyles, with fast-running metabolisms to match. Everything from growth rates to diet to integument has been used as evidence that dinosaurs, if not as fully “warm-blooded” as mammals, at least ran on a higher octane than many modern ectotherms. (“Cold-blooded” and “warm-blooded” are misleading terms; some ectothermic reptiles, such as large marine turtles, maintain consistently high body temperatures through behavioral adaptations, and some endothermic species, such as hummingbirds and bats, have a wildly variable body temperature that periodically drops low enough to drop them into torpor. Poikilothermic = variable temperature, homeothermic = consistent temperature, and endo- or ectotherms can be either.)

There is a new paper in PLoS ONE today that jumps into the fray of the dinosaur energetics question. Pontzer and Hutchinson (2009) test the hypothesis that dinosaurs were endothermic, using biomechanical analysis to model the metabolic rate of 13 bipedal dinosaurs, in addition to an outgroup ornithodiran, Marasuchus. They calculated metabolic demands of both walking and running using locomotor anatomy (limb length and active muscle volume), and compared their results to the aerobic capacity of extant ectotherms and endotherms. These comparisons can give us clues where the dinosaurs might have fallen along this metabolic spectrum.

So, what did they find? The results showed strong evidence that dinosaurs had aerobic capacities that exceeded the maximum limits of extant ecotherms. In other words, they were most likely endothermic to at least some degree, otherwise they could not have afforded the amount of energy that it apparently cost them just to move around. It is suggested that development of endothermy could be a reason for the long and extensive reign of the dinosaurs, which continues to this day in the form of their avian descendents.

It is certain that the debate over dinosaur energetics is far from resolved, but this study definitely adds a fascinating piece to the puzzle.

Pontzer, H., Allen, V., & Hutchinson, J. (2009). Biomechanics of Running Indicates Endothermy in Bipedal Dinosaurs PLoS ONE, 4 (11) DOI: 10.1371/journal.pone.0007783

National Geographic has an interesting report on predator-prey issues in national parks: apparently pregnant moose in Yellowstone National Park and Grand Teton National Park tend to shift their activity closer to roads before giving birth, in order to avoid predation by grizzly bears.

According to the results of the study, bears tend to be much more wary of roadways than moose. Grizzlies usually give keep at least a 5000 meter clearance, while moose have been recorded giving birth within a scant 45 meters of a road.

One question that needs to be asked immediately is: how do we know moose are doing this to avoid predation? What if they’re just not very bright and haven’t figured out to avoid the roads themselves?

The study answers that question by showing that moose only show this pattern of behavior in areas where bears are present, and that pregnant females have shown closer and closer associations with roads over the years as bear populations have increased in the parks where the research was conducted. Also, it is noteworthy that only pregnant females showed this pattern, which also supports the hypothesis that this is an anti-predator behavior being used to decrease mortality of newborns.

I’m pursuing a career in carnivore conservation, and am extremely intrigued by any story about animals adjusting complex behaviors in response to anthropogenic influences. It would be interesting to look at why bears are so more adverse to roads than moose. The article mentions that bears are more disturbed by the noise of the traffic, but I’d be interested to learn if there is more to it than that. Could it be due to different experiences with poaching, better associative learning abilities, larger home ranges in general, foraging preferences, or something else altogether?

One of the take-home messages from this study is that it’s important to consider information like this when planning parks and other managed areas. Something as simple as the layout of access roads can have a profound impact on the dynamics of populations and how they interact with each other, in ways that can’t always be predicted. Researchers from Denali National Park have studied the moose/bear populations there and have not found the same pattern of behavior as that reported from Grand Teton. Obviously, management plans should be tailored to specific populations, as opposed to automatically assuming that what works for a species in one setting will apply equally as well in another place/time.

Another example of this is an absolutely fascinating Journal of Mammalogy paper that I read recently, Selection of den sites by black bears in the southern Appalachians. This study (which also measured other parameters affecting site selection, such as elevation and slope), done in the Pisgah Bear Sanctuary in North Carolina, showed that females with cubs actually avoid gravel roads more than paved roads, despite the fact that paved roads are usually busier. This seems counterintuitive at first, with females choosing to den much farther from quieter gravel roads and closer to the higher traffic volumes associated with the paved roads in the sanctuary.

Why would mother bears prefer to be near higher traffic paved roads than less-traveled gravel ones? The authors of the study suggest that it is due to the fact that human behavior on paved roads is much more predictable. If you’re cruising down a paved road at a relatively high speed, keeping up with the flow of other cars, chances are that you’re not going to stop, get out, and dally around the roadside.

Gravel roads, on the other hand, are more likely to be used by hikers, campers, and other people that intend to roam around the forest (maybe even pesky biologists? ;P ). Also, the authors suggest that poaching pressure (it appears that this does occur even inside the preserve, unfortunately) could be a factor as well. Male bears and females without cubs didn’t show the stronger aversion to gravel roads, but females with cubs did, suggesting that the avoidance behavior is a defensive mechanism aimed at protecting their offspring from unpredictable intruders.

If the bears have learned that human activity is less predictable when people approach on a gravel than a paved road, it makes sense that females will avoid these areas when they are choosing den sites to house their cubs. I found this to be extremely interesting; I wouldn’t have expected a stronger aversion to gravel roads, but the explanation is pretty convincing when you see all of their data.

Moral of these stories: road layouts within wildlife preserves are complicated by multiple factors, and animals sometimes react to them in ways that initially seem counter-intuitive to we mere humans.


Reynolds-Hogland, M., Mitchell, M., Powell, R., & Brown, D. (2007). SELECTION OF DEN SITES BY BLACK BEARS IN THE SOUTHERN APPALACHIANS Journal of Mammalogy, 88 (4), 1062-1073 DOI: 10.1644/06-MAMM-A-329R1.1

(Repost from my old blog archives, originally posted 10/13/2007)
(Image source)

Apparently the hunting season for wolves opens on September 1 (next Tuesday), and the state of Idaho is charging residents $11.75 a head for kills. Wolves have bounced on and off of the Endangered Species list for years now, with their status often more a result of the political environment than anything else. Currently, populations of wolves in the Great Lakes Region are protected, but those in the Rockies are not.

Idaho has set a season quota of 220 individuals, 25% of the wolf population in the state, and 13% of all the wolves currently inhabiting the Northern Rocky Mountains. While residents can bag a wolf for little more than the price of a movie ticket, non-residents pay a higher bounty of $186 for a wolf tag. That still seems to be a bargain, though, when you consider some people regularly spend that much money on coffee or gas every month.

Several groups are currently filing lawsuits to stop the state authorization of wolf-killing, although some officials fire back that people will kill wolves whether it is legal or not. This is true, some degree of poaching or “self defense” killing is almost inevitable. It seems, though, that if we are to make any progress with conservation there has to be solidarity between scientists and government in communicating the importance of the roles that predators play in their ecosystems. I agree that hunting is justified for some species, but not for an imperiled carnivore that is only beginning to recover from the brink of extinction.

Hunting advocates claim that wolf populations are growing too fast and must be controlled by humans. As Linnell et al. (2002) point out, though, “in many situations human tolerance for carnivore presence may well be lower than ecological carrying capacity.” In fact, records show that wolf densities were once highest in areas where they are currently extinct (Riley et al. 2004). As I mentioned in my last post, we have little to no evidence for “natural” densities of large carnivores prior to human hunting, but it is widely agreed that the paltry populations that some officials advocate are far below the numbers that will allow natural genetic, social, and ecological dynamics.

There is a wide spectrum of opinion as to how much intrinsic value and respect wild animals deserve, but seriously, $11.75? That just makes it seem too easy and accessible. I wonder what algorithm was used to calculate that price? Everyone with a weapon and nothing better to do is going to be clambering for a license and roaming the backwoods, hoping to bag one (or more) of these “prizes.”

References:
Linell, D. et al. 2002. The Linkage between conservation strategies for large carnivores and biodiversity: the view from the “half-full” forests of Europe. In Large Carnivores and the Conservation of Biodiversity, J. Ray, K. Redford, R. Steneck, and J. Berger, eds. Island Press, Washington, D.C. pp 381-399.

Riley, S, et al. (2004). Dynamics of early wolf and cougar eradication efforts in Montana: implications for conservation Biological Conservation, 119 (4), 575-579 DOI: 10.1016/j.biocon.2004.01.019

I did my undergraduate degree at Auburn University, which is both a fantastic research institution and (in my exceedingly biased opinion), the crown jewel of Southern college football. I have spent many autumn Saturdays crammed in Jordan-Hare Stadium with 87,000 other people (keep in mind that the entire population of the town is around 40,000), and never ceased to be amazed at such a huge aggregation of humans, all there just to watch a game. The conservation biologist in me always felt some melancholy in contemplating the numbers, however, because the fans for just one game outnumber the population of some entire species by orders of magnitude. This is, ironically the case with Auburn’s mascot species, the tiger. If you took every single wild tiger left on the planet and put them in Jordan-Hare, they would fill little more than a single one of the 45 sections in the bleachers.

The tiger (which includes 6 extant and 2 extinct subspecies) is one of the most enigmatic and majestic species gracing our planet, and they have long been a flagship species for conservation efforts. A new PLoS Genetics paper by Mondol et al. brings news that may be seen as both ominous and auspicious for tiger conservation efforts.

The bad news: tiger populations have essentially been devastated to the point of near-extinction. The authors found that current tiger populations amount to only 1.7% of the tigers found historically, and are restricted to an almost insignificant 7% of their original range.

The good news: widespread sampling efforts showed that the Indian tigers retain 76% of the genetic diversity found in tigers worldwide. This indicates that the tigers’ genes are not disappearing as fast as their population numbers. For programs dedicated to preserving genetic diversity of declining species, this is a cause for celebration and hope.

These insights into the genetic structure of Indian tigers also yield clues to the tiger’s history. Mondol et al.’s analysis of the diversity patterns indicated that about 200 years ago, tigers in this region underwent a significant population crash, most probably human-induced.

This is indeed fascinating. I am becoming skeptical and jaded in my old age, however, and I am increasingly concerned that the public will get the impression that we can claim conservation success merely by preserving genetic diversity. Much has been made of “minimum viable populations,” “maximum sustainable yield,” and the like, with too little regard for the integrity and function of food-webs, and the resulting impacts on not only predators and prey but the ecosystem as a whole. Humans had been doing their best to eradicate large carnivores long before our historical and scientific records began. We would not know how large Indian tiger populations were several centuries ago if analyses like the ones in the current PLoS paper did not allow us to create estimates from molecular evidence. This makes it extremely hard to set appropriate goals for conservation and management plans.

Large carnivores are often the first species to go extinct or decline under stressful ecological conditions (whether anthropogenic or otherwise), and after they are gone their communities often shift from top-down regulated trophic structure to an alternate stable state with bottom-up regulation (Beisner et al. 2003, Steneck et al. 2002). In a sense, the only “natural” state we have ever observed has been one of depleted predator populations. Therefore, conservation efforts that seek to restore populations to a “minimum viable” number or to densities that match historical records may still be setting the bar far too low for predators to fill their ecological roles in regulating mesopredators and herbivores, which in turn affects smaller non-prey animals and plants, which affects water and soil nutrient content and the physical structure of the habitat itself. We might be able to preserve all of the genetic diversity of a species in a lab, and may even re-establish self-sustaining populations in the wild, but that does not mean that we have restored them to the densities and distributions required for them to perform the ecological roles that they played in their communities prior to relatively recent population crashes. Habitat loss and degradation is one of the most critical factors threatening biodiversity today, and as Mills (2003) points out:

“Biodiversity is a broad concept incorporating compositional, structureal, and functional attributes of ecosystems at four levels of organization—namely, landscapes, communities, species, and genes” . . . “the greater the range of ecosystems that can be conserved to accomodate large carnivores, the greater will be the number of opportunities for these variable interactions to be played out and for adaptations to changing conditions to evolve.”

Even if we had a complete tiger genome on hand, it would not do much good if the animals are relegated to zoo cages or small ecotourism resorts. Even if a token number of animals are allowed to roam in the wild, the species would simply be lingering as a present and yet enfeebled shade of its former self, with its role in community interactions and regulation essentially paralyzed.

Don’t get me wrong, genetic diversity is still an crucial factor, and the results of this paper are both important and fascinating. This information gives us further clues as to the size and distribution of historic tiger populations, which can lead to further analyses of predator-prey relationships and ecosystem interactions. The news about the remaining genetic diversity is encouraging; inbreeding depression can potentially prevent species from ever recovering from extremely low population numbers, even if their habitat is restored.

I suppose I just worry that we will lose sight of the forest for the trees, (or maybe lose sight of the tigers for the stripes, if I may put a spin on the metaphor?), and run the risk of congratulating ourselves for meeting artificially low bars due to shifting baselines of predator densities. The important thing is to keep in mind that conservation efforts cannot be broken down into parts; species they must be treated as integrated wholes, “package deals” including genes, physiology, behavior, and role in community interactions.

Mondol, S., Karanth, K., & Ramakrishnan, U. (2009). Why the Indian Subcontinent Holds the Key to Global Tiger Recovery PLoS Genetics, 5 (8) DOI: 10.1371/journal.pgen.1000585

See also:
Beisner, B.E., D.T. Haydon, and K. Cuddington. 2003. Alternative stable states in ecology. Frontiers in Ecology and the Environment 1(7):376-382.
Mills, M. G. L. 2003. Large carnivores and biodiversity in African Savanna Ecosystems. In Large Carnivores and the Conservation of Biodiversity, J. Ray, K. Redford, R. Steneck, and J. Berger, eds. Island Press, Washington. pp 208-229.
Steneck, R., M. Graham, b. Bourque, D. Corbett, J. Erlandson, J. Estes, and M. Tegner. 2002. Kelp forest ecosystem: biodiversity, stability, resilience, and future. Environmental Conservation 29: 436-459.

(For information on the Auburn chapter of the Society for Conservation Biology’s Tigers for Tigers program here.)

Harvesting wind power is a fast-growing form of alternative energy technology, and U.S. interest in the wind industry is growing, as we work towards diversifying our energy grid. New turbines are being erected across the nation, and the prospects for using wind to supplement our power supply are positive.

As with any form of technology, there have been, and will be, some collateral damage to wildlife and the environment. Although the effects of reducing oil consumption should outweigh the detrimental impact of wind turbines in the long term, researchers strive to minimize immediate negative effects as much as possible.

One issue that has been raised in the conservation community is that the turbines pose a threat to flying animals, with special attention to birds and bats, which have been shown to suffer significant mortalities on wind farms, especially for migratory tree-roosting bat species. Significant losses among populations of endangered species such as the Indiana bat and the gray bat.

A recent paper in PLoS ONE reports evidence that electromagnetic radiation from human sources-such as air-traffic control and weather radar-can deter bats from approaching the turbines, reducing mortalities (Nicholls and Racey 2009). The study involved experiments conducted in Britain, in which radar antennae were mounted in bat foraging areas. The authors measured both bat foraging activity (determined by detecting the foraging calls the bats use to locate prey) and insect abundance in the radar zones and in control areas without the radar emissions. Both rotating and fixed antennae were used, and fixed antennae were divided into two treatments with different emission pulses.

Results showed that the electromagnetic signals did indeed deter bats within 30 m of an antenna, although it did not entirely cease foraging activity in the area. The most effective treatment was the fixed antennae with a medium pulse rate (1200 Hz). Insects did not seem to be affected, however, as no significant difference in insect abundance was detected between experimental and congrol zones.

(Table 3. Statistical significance of differences in bat activity between control and experimental trials (*) denotes a significant result for both corrected PBonferroni (P values×number of comparisons) and uncorrected P-values.)

Although details of technical aspects such as optimal pulse rates, wavelengths, and orientation will still need to be refined, this study suggests that there are ways to mitigate bat mortalities on wind farms. Electromagnetic pulses that decrease foraging activity in the vicinity of wind turbines can substantially reduce mortalities. It will be interesting to follow the story and see if strategic location of wind farms near radio towers or other background emitters can reduce the costs and effort needed to set up these deterrent systems.

This issue also raises questions as to how the electronic signatures of our modern lives-our cell phones, wi-fi, microwaves, remote controls, radio, satellite TV, etc-are affecting the organisms around us. Studies suggest that sonar and oil drilling affect the behavior and health of marine mammals, and it seems that similar studies on volant animals would be interesting.

This could have applications for both conservation and human health, as we are by no means immune to our own radiation. (You can find information on radiation from various cell phone models here, if you are concerned). This is not to say that the paranoia about cell phone signals and other electronics causing cancer are anything to become upset and lose sleep over (I am not promoting the radiation hysteria! Some people take these worries to an extreme, but, as with anything, moderate and reasonable caution is warranted). This will definitely be an interesting line of study to follow, and hopefully research studies such as the one by Nicholls and Racey will help to mitigate impacts as we seek to progress with our energy technologies.

Nicholls, B., & Racey, P. (2009). The Aversive Effect of Electromagnetic Radiation on Foraging Bats—A Possible Means of Discouraging Bats from Approaching Wind Turbines PLoS ONE, 4 (7) DOI: 10.1371/journal.pone.0006246

The Salinas River Valley is apparently being terrorized by a new salamander “superpredator,” resulting from interbreeding between the California tiger salamander (Ambystoma californiense_) and an introduced species, the barred tiger salamander (Ambystoma tigrinum mavortium_). According to a fascinating new study conducted by a group of researchers from the Center for Population Biology at UC Davis and the University of Tennessee at Knoxville, the hybrid offspring grow much larger than either parent, with massive mouths that allow them to consume a much wider variety of amphibian prey, including rare frogs and salamanders such as the Santa Cruz long-toed salamander (Ambystoma macrodactylum croceum.)

Apparently the hybrids will not only consume other amphibians, they will also eat larvae of native species, a behavior not seen in their parents’ foraging patterns.

Even when the hybrids are tadpoles themselves, their predatory adaptations are the stuff of horror movies: some of them develop extra rows of teeth so they can cannibalize one another, a phenomenon also absent from the parent species.

Definitely makes for an interesting case study in hybrid vigor (aka heterosis or outbreeding enhancement. This is also bit of a conservation quandary, because although the hyper predatory behavior of these salamanders is threatening native species, they are also carrying on the genes of the endangered A. t. mavortium. The outlook for genetically pure populations of this species is grim, and this new bully species could be the only way to carry on the genes. The National Geographic report on the study includes this commentary from the study leader:

“Getting rid of the hybrid poses “ethical quandaries,” study leader Ryan said.
“From a conservation perspective, there [are] a lot of deep questions about what to do with this,” she said.
After all, the hybrid is part endangered species, so “do we protect [them] because they’re part native?”
Overall, Ryan said, her “real concern” is for the survival of California’s native salamander, which has shown to be no match for the half-Texan interloper.
The hybrid’s more aggressive predation “benefits the hybrid and harms the native, speeding up the process of converting populations into more hybrids.”

Personally, I don’t think that preserving the genes in this hybrid really counts as preserving the species, especially if it puts a multitude of other species at risk. Remember that if it were not for human introduction of the barred salamander, these hybridizations would not have occurred, so it cannot be considered “natural” in a broad sense. I have always viewed “species” as a label including not only genetics, but behavior and ecological role as well. This is why I am not a fan of zoos as primary conservation tools for large mammals (although I acknowledge their utility for public education). Take away ecological context, and you might have similar DNA, but the species itself is still lost.

So, what say you, is allowing this new hybrid to persist a responsible conservation strategy, or a conservation nightmare?

Ryan, M., J. Johnson, and B. Fitzpatrick. 2009. Invasive hybrid tiger salamander genotypes impact native amphibians. PNAS doi:10.1073/pnas.0902252106

(Credit for image of California tiger salamander)

One of the general trends seen throughout the animal kingdom, and especially within Class Mammalia, is a scaling of longevity to body size. Elephants live longer than horses, which live longer than mice. There have been many, many studies which attempt to parse out the reasons for this, ranging from metabolism and fecundity to intracellular transport and skeletal biomechanics. As with many phenomena in biology, however, there are indeed exceptions to the rule, and these cases can be extremely instructive.

This brings us to bats. One of the many fascinating aspects of bat biology is that their lifespans are much higher than would be expected for their body size. Most bats are comparable in mass and volume to small rodents, and yet they live much longer than their terrestrial friends. For example, Tadarida brasiliensis_, a common North American species, weighs 10-20 grams, approximately the same as a lab mouse. And yet, while mice are usually lucky to reach their third birthdays in captivity, captive bats have been known to live for up to 20 years. Anecdotally, at one field site in Mexico we saw vampire bats (_Desmodus rotundus) that had been tagged (as adults) nine years ago.

Why the discrepancy? Why do bats violate the scaling rule?

A new study has recently added a new piece to the the puzzle of chiropteran longevity. Salmon et al. examined extracted proteins from liver samples of T. brasiliensis and Myotis velifer, and then treated the proteins with chemicals known to induce mistakes in protein folding. They then compared the proteins to samples from mouse livers that had been exposed to the same chemicals.

The results were fascinating: the bat proteins showed significantly less misfolding and damage than the mouse proteins, suggesting that bat proteins have some adaptation that allows them to maintain their structural integrity under conditions that warp the proteins of other mammals. The bat samples had lower levels of both protein ubiquitination (which functions to label proteins for degradation by proteasomes) and overall proteasomal activity, in addition to lower levels of carbonylation, the signature damage caused by oxidation. All of that, in a nutshell, means that the bat proteins were much hardier under stress. The authors suggest that bat longevity “is correlated with resistance to protein oxidation and enhanced protein homeostasis.”

It will be very interesting to follow this vein of research. How significant is this phenomenon in other bat species? In the study, T. brasiliensis showed more significant damage resistance than M. velifer_. Bats, comprising 20% of all mammal species, are incredibly diverse in both morphology and lifestyle, so it would be interesting to look at representatives from each family. What about megachiropterans, the large fruit bats which some have suggested may actually be more closely related to primates than microchiropterans? (This hypothesis doesn’t have widespread support, but it makes for an interesting argument, see this booksGLXltMC&printsec=frontcover&dq=bats+biology+and+behavior for a well-rounded discussion of the evidence that supports and refutes the idea)

I am not an ornithologist, but I have often wondered about exceptions to the scaling rule amongst birds, with small parrots often having much longer lifespans than eagles. It would be interesting to see a study similar to Salmon et al. on different vertebrate taxa.

And of course, further work can look more closely at what mechanisms exactly allow bat proteins to resist oxidation and therefore prolong senescence. Some journalists are already making many loud claims about the study uncovering a “fountain of youth,” implying that a human therapy could result from a better understanding of this phenomenon. This is a true possibility, but it seems a bit early yet to start making promises.

Still, you have to appreciate the sheer luck of some species: bats get to fly AND eat the equivalent of their entire body weight every night, and they have extended lifespans to allow them to enjoy these pleasures for many years. Sigh.

References:
Altringham et al. 1998. Bats: biology and behaviour. Oxford University Press.

Salmon et al. The long lifespan of two bat species is correlated with resistance to protein oxidation and enhanced protein homeostasis. The FASEB Journal, 2009; 23 (7): 2317 DOI: 10.1096/fj.08-122523*

Photo credit: S. Pederson, Nevis Biodiversity Project

A post over at Effect Measure last week reported on this CDC study, which details an outbreak of H1N1 flu amongst the giant anteater (Myremecophaga tridactyla) at the Nashville Zoo.

This caught my attention, because part of my honors thesis involved observing giant anteaters at the Montgomery Zoo. After spending hours and hours a day recording their every movement for an entire summer, I became a little bit attached to them, even though this species was not the main focus of my research. (That portion of my thesis focused on how the activity budget and exhibit utilization of the maned wolf, Chrysocyon brachyurus, changes when sharing an enclosure with another species).

These guys are one of the true oddballs in the mammal world. They lack teeth, able to eschew oral mastication because of the presence of hard growths further along their digestive tract, aided by sand and small rocks that are often found in their stomachs. Most mammals using gastroliths to help digestion are marine (otters, whales, etc), so the giant anteater represents a completely independent evolution of the feature. They are famous for their incredibly long tongues (perfect examples of convergent evolution with other ant-specialists such as the aardvark, pangolin, and some bat species), and they have the endearing habit of carrying their babies around piggy-back style.

In my observations at the zoo, I was also struck by the extreme, um, lack of intelligence of this animal. It was astonishing, really. I would watch the zookeepers try to get the Montgomery anteater onto the exhibit each morning, and sometimes it would take over 30 minutes for it to move 12 feet from its holding pen through the door to the enclosure, because it would just wander around in corners, lost in whatever passes for anteater thoughts, I suppose, even though its breakfast lay on the other side of the door. This was after it had been going through the same routine for three years. Apparently, for M. tridactyla, each morning is a clean slate. This is entirely anecdotal, of course. I am not aware of any studies that have been done on anteater cognition, but their cranial capacity to body size ratio is quite low. Their body temperature is also quite low, which can sometimes correlate to “intelligence” in mammals (how to actually define intelligence is way off-topic and out of the scope of this post, unfortunately).

So, that’s a brief sample of why the giant anteater is interesting, but the recent news makes it even more intriguing. The CDC reports that H1N1 virus was cultured from samples of nasal discharge, which was collected from the animals in February. This strain appears to be closely related to the human H1N1 virus that bloomed around the country during that time. Two of the three animals showed seroconversion (evidence of infection, most often referred to in the context of HIV infection), and the third “appeared to have been exposed to and infected with influenza virus a year before the described outbreak.”

As for the differences between the anteater and human strains, the report states that they were not functionally or antigenically significant, and that the most likely scenario is that the anteaters acquired the virus from exposure to human caretakers. They were unable to tell whether the virus spread from one animal to the next, or if each individual contracted the virus from the caretakers independently.

This is all very intriguing. Apparently no other species at the zoo showed signs of contracting the virus, so what was it about the anteaters that made them susceptible? One would assume that primates might be most vulnerable to contracting a human virus, but that’s not always the case, of course. I’m not sure if there are any boar or other swine species at the Nashville Zoo, but I’m sure there are other perissodactyls, none of which contracted whatever the people were carrying. Most zookeepers do not tend to a single exhibit, especially for animals as low-maintenance as the anteaters, so I can’t imagine that these animals were just unlucky enough to have the only virus-carrying keepers in the entire zoo. The anteaters have such a low body temperature compared to other animals, it seems that the habitat they provide for pathogens may be much different.

All of this is an important reminder of why zoological monitoring is crucial for the management of disease outbreaks, in addition to human and public health measures, for both the flu and other circulating pathogens. Even if a virus jumps to a species that is a low-risk carrier (how many people are exposed to giant anteaters on a regular basis), such incidents can provide critical clues as to the nature of a virus and its ongoing evolution.

A few weeks ago, we discussed how ecological factors influence offspring sex-ratio in elephant seal populations. Mammals (among other vertebrates) can optimize their reproductive investment by producing either males or females under difference circumstances, but there is another aspect to managing investment also: how many? Superficially, it seems that, of course, producing more babies is more advantageous. The more youngsters produced, the bigger chance of parental genes being sustained in the population. But, wait, offspring are expensive. So if more energy is concentrated into fewer offspring, you can invest more per capita and set them up for a higher chance of survival. So what is a mammal to do?

As with most things, the answer is “it depends.” Different species require different strategies. This should all be a review, if not then refer to information on K- vs r-selected life history patterns.

We already know that different species employ different methods, based on their ecological and evolutionary history. It is interesting, therefore, to zoom in on individual species that can manipulate litter size, to examine the relative advantages or disadvantages of offspring number. In a study recently published in the Journal of Mammalogy, a team of researchers has focused on the results of twinning in mule deer (Odocoileus hemionus), with some interesting results (Johnstone-Yellin et al. 2009).

The researchers tracked litter size and fawn survival rates in a population of mule deer in eastern Washington. In a nutshell, they found that singleton fawns had a significantly higher survival rate than twins. In addition, previous work has shown that it takes 1.6 times more energy for a female deer to raise twins than if she only produced a single fawn per season (Mauget et al. 1999).

At first glance, all of this seems fairly predictable and mundane. We have to wonder: if twins are less likely to survive, why do so many of these females produce them in the first place? Almost half (14/30) of the fawns in the study were twins. Surely there would have been selection pressure against such a prevalence? That leads us to the interesting part: the data suggests that females producing twins actually increased their reproductive success, despite the higher fawn mortality and increased energy expenditure involved in raising twins.

How does this work? Over half of the offspring in this study (16/30) died by the end of the summer. Singletons were more likely to survive (they had a 62.5% chance of surviving, versus only 40%) for twins, and among the fawns that died, singletons lived longer (69 days versus 16 days for twins).

Despite the depressing outlook for twins, the numbers also showed that mothers of twins produced an average of 0.92 fawns, while mothers of singletons averaged only 0.75. The mortality rate for the offspring is so high, that there is a very strong chance a female’s fawn will die regardless of litter size. Thus, having a back-up baby ends up being advantageous in the end, which is why twinning (some females actually produce triplets, also) has been sustained in the population over time. For many animals, especially prey species such as deer, the choice is sometimes not win or lose, but lose or lose less. It may sound grim, but it is an effective strategy: Johnstone-Yellin et al. determined that a the population in which all females produced twins would have a 4% higher growth rate than it would have if all females produced singletons.

Studies such as these are important for more than just clarification of life history information for a given species. This reinforces the importance of looking at the proverbial “big picture” when addressing topics with evolution, ecology, and behavior. You have to extrapolate across seasons, years, and populations in order to see the true significance of many survival and reproductive strategies.

Further research is needed to determine how twinning affects a female’s lifetime reproductive success. Will twins in one year be a detriment to her performance as a mother in following years? There has been much work done on manipulation of clutch size in birds, but studies such as the Johnstone-Yellin et al. paper are slowly shining light on how the issue is handled within different mammalian species.

Johnstone-Yellin, T., L. Shipley, w. Myers, and H. Robinson. 2009. To twin or not to twin? Trade-offs in litter size and fawn survival in mule deer. Journal of Mammalogy 90: 453-460.
Mauget, C., R. Mauget, and A. Sempere. 1999. Energy expenditure in European roe deer fawns during the suckling period and its relationship with maternal reproductive cost. Canadian Journal of Zoology 77: 389-396.

(Image credit).

In a perfect world, conservation would simply be a matter of identifying species at risk, passing policies to prevent harm to the organisms and their habitats, and watching their numbers rebound accordingly. Unfortunately (and in case you haven’t noticed…), ours is anything but a perfect world. The political and social squabbles about conservation are a topic that can/have/will be batted around endlessly, but nature itself presents complications as well, as a recent case in Maine illustrates.

Apparently Great cormorants (Phalacrocorax carbo_), which are not classified as endangered yet, are on the downslide in New England. The number of breeding pairs remaining in in Maine is down to less than a third of the number found there 15 in 1995. There are, as usual, multiple reasons for their decline, but apparently one significant factor is that they suffer high mortality in the claws of bald eagles (_Haliaeetus leucocephalus), which have been progressively rebounding from near-extinction several decades ago.

While bald eagles are no longer on the U.S. Endangered Species List (removed in 2007), they are covered by both the Bald and Golden Eagle Protection Act and the Migratory Bird Treaty Act, which means it is illegal to kill, period.

This is where the conundrum comes in. We have the cormorants facing serious declines. One of the key reasons their populations in Maine are crashing is predation by eagles. Unfortunately, the cormorants lack any legal protection, but the eagles-which have had increasingly healthy populations for years now-are covered under multiple articles protective legislation, and are essentially untouchable. What to do?

This isn’t the first time that successful eagle conservation has caused problems. Years ago, studies showed that golden eagles (Aquila chrysaetos_) were causing massive declines in the populations of island foxes (_Urocyon littoralis) in the Channel Islands. The foxes faced extinction, but there was almost no way to control the populations of eagles on the islands. Again, what to do?

It should be noted that the eagles are not the villains in these stories. In both cases, the eagles were forced to change their typical hunting strategies due to human disturbances. Bald eagles are fish specialists, but the coasts of New England have become so over-harvested that the birds cannot find enough fish to sustain themselves, and must resort to preying on other birds.

Golden eagles are more likely to prey on mammals, but historically did not inhabit the Channel Islands in large numbers, until humans introduced pigs to the islands. The eagles moved in shortly after, and populations grew up around the tasty supply of pork. Once the birds had exhausted the pig supply, they had become established in breeding territories, and so instead of leaving the islands, they switched to foxes as their primary food source.

In the Channel Islands case, human intervention was required. Instead of killing the eagles, translocation efforts were made, and golden eagles were shifted from the islands to the mainland. At the same time, bald eagles were moved from mainland to the islands, to restore the original ecological balance. (Bald eagles used to inhabit the islands, until DDT pollution caused massive declines in the mid-20th century). Baldies are fish specialists, so pressure on foxes was relieved while maintaining a healthy population of raptors.

The recent bald eagle situation is trickier, though. It is not limited to Maine: there are reports of eagles decimating seabird populations in Alaska, consuming blue heron chicks in the midwest, and ransacking flocks of waterfowl on their migratory routes. On the surface, this may seem like a Big Bad Bird issue, with the eagles gaining numbers and bullying other species. Brad Allen, who works with the Main Department of Inland Fisheries and Wildlife, has said “They’re like thugs. They’re like gang members.” In reality, though, it’s about the fish. Most of our conservation legislation covers habitat and the organisms themselves, but all species are parts of complex webs of interactions within their ecosystems, and effective conservation involves their prey base, their predators, their prey base’s resources, on and on . . . in nature, the multitude of connections makes it very hard to know quite where to draw a line around what should (or, more importantly, what can) be covered by a program.

For example, the eagles in Alaska are killing seabirds because fish populations are dropping due to disappearing kelp beds. Kelp forests are decreasing due to over predation by sea urchins. Urchin populations are growing due to decreasing predation by sea otters, which are facing severe declines due to increasing populations of orca whales. So, more whales means more eagles, which means less seabirds. Orcas and eagles must be the criminals, should we just cull them and let everyone else recover? And open up all kinds of loop holes for people of questionable intentions to start killing whales and eagles? My head is starting to hurt, how about yours?

The unfortunate reality about conservation is that, well, it exists in reality. This means that hard decisions must be made and compromises are unavoidable. One of the take-home messages about the cases above is that it is much, much harder to restore a system once it is out of whack than it is to simply not let it become profoundly disturbed in the first place. That, however, would require both foresight, concern, and proactive problem solving from many different aspects of the government, economy, and society….

Further reading:
Bald eagles running off bird populations
Reisewitz, S. E., J. A. Estes, and C. A. Simenstad. 2006. Indirect food web interactions: sea otters and kelp forest fishes in the Aleutian archipelago. Oecologia 623-631.
Roemer, G. W., c. J. Donlan, and F. Courchamps. 2002. Golden eagles, feral pigs, and insular carnivores: how exotic species turn native predators into prey. PNAS 99: 791-796.