This blog post was originally published by Columbia Science Review in November 2013.
Video edited by Alexandra DeCandia. See credits for image sources.
By Alexandra L. DeCandia
You can tell by the way she uses her walk... that something's wrong. Tail outstretched and wings akimbo, the killdeer (Charadrius vociferous) cries aloud, limping along the rocky shore as if unable to fly. She appears injured, pained, and consequently, an easy target for any predators in the vicinity. Walk, squawk, falter. Enemies follow every movement of this pathetic scuttle and trail closely behind. Walk, squawk, falter. They near her position. Walk, squawk, falter. They open their mouths. Walk, squawk – the killdeer flies away. She circles the beach and, once her deceived predators have vanished, returns to her eggs hidden in the rocks.
This distraction display of a devoted plover mother is one example of an anti-predator adaptation in the animal kingdom. Driven by the urge to stay alive and filtered through the finely toothed comb of natural selection, numerous strategies have evolved to protect prey species from voracious foes. While some have adopted fairly common tactics, such as hiding in herds (“dilution of risk”) or mimicking poisonous species (“Batesian mimicry”), others have erred on the side of unique innovation. Cuttlefish, horned lizards, and common potoos all fall into this latter category, and like the thespian killdeer, possess sublimely bizarre means of protection.
Cuttlefish (Sepia officinalis) are masters of visual crypsis. Lacking structures for self-defense (other than a deployable ink sack), these protein-rich invertebrates had to devise means of evading predators without being seen. Their strategy: camouflage. Unlike other organisms that bounce light off their scales (“reflective silvering”) or cover themselves with surrounding corals (“self-decoration”), cuttlefish have evolved the ability to alter their skin color to match any background. Manipulating the muscles surrounding roughly 20 million pigmented chromatophores and corresponding reflective cells, cuttlefish can change their color and pattern faster than any other organism on the planet. Therefore, at the first sight of a predator, cuttlefish immediately vanish, rendering their attackers dumbfounded and hungry.
North American horned lizards (Phrynosoma hernandesi) have a similar effect on their predators. However, their method of evasion is drastically different (and, in my opinion, horrifically traumatizing). When threatened by a potential attacker, these colloquial “horny toads” engage in deimatic displays in an attempt to intimidate their rivals. Puffing out their bodies for increased size, horned lizards resort to autohaemorrhaging if the predator doesn’t back down. A stream of red, noxious hemolymph propels from the corners of their eyes onto the face of their attackers. Stunned, the predator ceases its attack, thereby allotting the horny toad a hasty, albeit bloody, escape.
A far cry from the blood-infused-attack-of-strange employed by the horned lizard, the last anti-predator adaptation is one of peace, tranquility, and arboreal inspiration. Its innovator, the common potoo (Nyctibius griseus), is the elusive singer of the Central and South American night. With its characteristically bugged-out eyes and speckled gray feathers, the potoo is a nocturnal insectivore most at risk of predation during the day. Rather than seeking cover for these resting hours, though, the potoo boldly perches on the conspicuous remains of dead trees. Predators are rampant, but this seemingly easy prey eludes all captors by artfully employing mimesis. Head aloft, eyes closed, every muscle stilled, the potoo spends his day posing as the tree. He does not call, he does not move; he is the master of disguise, and he lives another day.
As is apparent from the above examples, anti-predator adaptations take a variety of forms. Whether an individual hides among a herd, or more dramatically feigns injury, matches its surroundings, ejects blood from its eye sockets, or steadfastly adheres to a tree, it is acting to stay alive. If the adaptation is a success, the animal will pass its genes to the next generation. If it is a failure, the adaptation will disappear. It may seem harsh, but through this process, natural selection produces the incredible diversity of behavior, morphology, and ultimate speciation that makes the study of non-human animals so fascinating, absurd, and, in the case of these prey species and their anti-predator defenses, delightfully bizarre.
This blog post was originally published by Columbia Science Review in November 2013.
By Alexandra L. DeCandia
The situation may be worse than we anticipated for the little brown bat (Myotis lucifugus). In a new study published by University of Illinois researchers earlier this week, it appears that the fungus Pseudogymnoascus (Geomyces) destructans (the cause of White-Nose Syndrome or WNS in bats) is even more resilient than previously thought. Able to colonize any complex carbon source found within the confines of a cave environment, the fungus can persist on a numerous organisms and at a variety of pH levels. For the little brown bat, this implies that any attempt at the fungus’ eradication from known hibernacula proves futile. The fungus will merely lay in wait on another organism until its preferred host reappears en masse each fall.
The North American strain of Pseudogymnoascus destructans (Gd) examined in this study first appeared in 2006. Infecting only a few hibernacula in upstate New York, the fungus has since spread to over two-dozen states and migrated as far northward as Canada. Highly transmissible, highly persistent, and incredibly lethal, Gd has already claimed the lives of over 5.7 million North American bats with no perceivable end to its destructive reign yet in sight.
Gd infects bats while they hibernate, passing from one individual to the next in the cramped conditions of a M. lucifugus colony. The fungus grows on the cold cutaneous tissues of their muzzles and wings and specifically degrades their epidermal keratin. Resultant lesions form and increase the bat’s vulnerability to other pathogens and parasites lurking within the caves.
Of even greater concern, though, is the fungus’ effect on the patterning of torpor and consciousness during hibernation. As an order, chiropterans possess incredibly efficient metabolisms. Flying or even heating their bodies above ambient temperature can deplete their energy stores to the point of emaciation within days. Therefore, remaining in a state of torpor (i.e. decreased body temperature, lowered metabolic rate, etc.) proves crucial when ambient temperature and food availability decrease in winter. Bats infected with Gd cannot remain in hibernation undisturbed, due either to fungal itch or rapid dehydration. With increasing frequency, they arouse until ultimately perishing from starvation.
Intrinsic value of the species aside, the loss of so many little brown bats at the hands of Gd-induced starvation poses a serious economic risk to North Americans. Through insect predation, consequential reduction in pesticide utilization, and natural agricultural pollination, bats provide ecosystem services worth an estimated $3.7 to $53 billion USD per annum (Boyles et al., 2011). Should WNS eradicate certain chiropterans from the continent as it seems poised to do (at least as far as M. lucifugus is concerned), thousands of metric tons of insects will pour into our fields and lead to a cascade of negative ecological, economic, and human health implications.
Combatting Gd and WNS has proven difficult thus far, to say the least. Studies have concluded that even if little brown bats manage to evolve means of surviving infection (as their European cousins have done), their populations will still decrease to fewer than 1% of their initial numbers within 20 years (Frick et al., 2010). Such estimates combined with the newfound resilience of Gd paint a grim depiction of the future for M. lucifugus, but they by no means necessitate surrender. Scientists continue to seek physical, chemical, and biological means of impeding the fungus, and some have even developed artificial hibernacula devoid of spores for bats to roost in unaffected. While neither management strategy has yet proven to drastically mitigate the spread of WNS, they represent steps in the right direction towards preserving an often overlooked but economically and intrinsically significant species, North America’s little brown bat.
This blog post was originally published by Columbia Science Review in October 2013.
By Alexandra L. DeCandia
With an ever-increasing frequency, one pudgy little marsupial is making headlines. Proclaimed the “Happiest Animal in the World” by Huffington Post some ten months ago, the quokka has since bundled into millions of hearts with its teddy-bear frame, cheeky grin, and characteristically social nature. Despite its near constant appearance on internet forums such as BuzzFeed and Reddit’s r/Aww, public awareness of the modern risks to quokka populations remains low.
Quokkas are one of the many species listed as vulnerable on IUCN’s Redlist (a wildlife conservation database). Due to their extreme endemism in the southwest corner of Australia and its two abutting islands (Rottnest and Bald), quokkas are particularly sensitive to habitat fragmentation, destruction, and climatic alteration. Unfortunately, as a result of human activities, quokka populations now face all three such threats. In fact, in a study conducted by Lesley Gibson et al. (2010), extinction is estimated to occur as early as 2070 if steps aren’t taken to drastically mitigate the species’ decline.
In order to combat threats afflicting native species, it is crucial for scientists to understand the exact causes of projected population declines. For quokkas, these causes are directly linked to their preferred habitats. In Australia, a continent marked by deserts and aridity, quokkas thrive as vegetative specialists. Nocturnal foragers, these herbivorous wallaby-relatives seek dense, shrubbery-laden habitats near swamps to permanently lodge their societies of 25-150 individuals. Historically, these habitats occurred in regions with 700 mm of annual rainfall. However, recent quokka populations have shifted to reside in areas receiving over 1000 mm of rain per annum as a defense mechanism. Small and ill-equipped to fend off predators with their chubby cheeks and tiny paws, quokkas rely on rain-fed vegetation for protection as well as nutrition. Seeking ample rainfall in an arid locale may not seem a winning strategy, but it is one that has obscured quokkas from dingoes, foxes, cats, and even large birds for millions of years. As humans alter the environment in unprecedented ways, though, the quokka’s strategy may no longer apply.
Foremost among risks to quokkas lies climate change. With the continued outpouring of anthropogenic greenhouse gases into the atmosphere, the overall temperature of our planet is increasing. For some areas, such as the northeastern United States, climate change will bring wetter conditions and more frequent occurrences of super-storms. For others, such as the entire continent of Australia, climate change spells increased heat-indices and ultimate desertification. Even the mildest models examining these rainfall alterations and projected quokka distributions predict ultimate range restriction. The most extreme models foresee extinction within our lifetime. Without dense vegetation afforded by ample rainfall, quokkas will be unable to defend against natural and introduced predators. Ultimately, they will be hunted to extinction as desert and suburbia afford little protection.
However, despite the gloom-and-doom nature of this Holocene Extinction, there exists hope for the quokka moving forward. In the best-case scenario, mankind can halt climate change, eradicate introduced predators, reconnect fragmented habitats, and expand the quokka’s current range to encompass greater (and wetter) regions. In a more realistic scenario, man can limit further greenhouse gas emissions, control invasive predator populations, conserve existing habitat, and design an action plan for species relocation should their current range ultimately disappear. The bottom line is that quokkas do not have to die. Steps can be taken towards their protection.
The quokka is just one species currently staring at the face of extinction. As human populations continue to grow at astronomical rates, it becomes our duty protect those we have harmed in our meteoric rise. Studying the effects of climate change on endemic species and managing their recovery programs before their necessary institution is and should be our present reality. Otherwise, we risk the loss of those species that make this planet worth the fight. Otherwise, we risk the loss of that contagious smile of the world’s happiest animal.
Welcome to the EEBlog! This page links to blog posts DeCandia lab members have written about wildlife conservation & the environment. It also includes posts written for other outreach platforms. Please see linked websites for original versions, when applicable.