If you're this guy, you pick potatoes. If you're me, you pick donuts. Either way, you're looking at a very limited diet for the rest of your life, with little to no nutrition. You would also become very dependent on the supply of that particular food. If donut shops ceased to exist, I would die a very slow, painful death and my species would slowly disappear. This is essentially what's happening to a couple endangered species like the North American snail kite and the monarch butterfly: they're picky eaters and it's killing them.
Selective Palate and Critical Numbers
Snail kites have special curved beaks and long claws that allow them to eat apple snails straight from their shells. They find most of these snails in the Florida Everglades, a place that offers an intricately linked ecosystem unlike anywhere else in the world.
Unfortunately, their claim to fame is also their downfall. These picky eaters restrict their diet to the apple snail and the apple snail only. Their selective eating habits, coupled with natural disaster damage to their homes, have led scientists to witness the swift decrease in their numbers, making them a critically endangered species. The decline has been so significant, that the population went from 3,500 in 2000 to only 700 in 2007 and has since faced extinction.
The atypical longevity of these birds have attributed to difficulties in studying their evolutionary patterns. According to a study done on the snail kite's specific diet, most research is done on plants and invertebrates with shorter generation times (less than a year). The snail kite typically lives to about 8 years old, making it challenging to study their long term effects, thus postponing the question of whether the changes that occur happen due to evolution or phenotype plasticity.
Similar to it's airborne brethren, the monarch butterfly is yet another species facing critical shifts in the evolutionary process due to diet. Most people have no problem associating the monarch with Milkweed, the herbaceous perennials with over 140 different species. The butterfly will deposit its eggs on the bottom of the leaves, which will later become the food source for the young caterpillars. But what most people don't realize, is that the very plant that gives these beautiful insects life, can also be a source of fatal parasitic action.
Tropical milkweed, one of the various species of the plant, doesn't die back and slough off old vegetation in the winter the way other milkweed does. Because of this, it is especially susceptible to the parasite Ophryocystis elektroscirrha (OE). The parasite gets ingested by monarchs as caterpillars when they hatch from their chrysalises, marking them with spores that leave them significantly weaker than non-infected butterflies.
According to Science magazine, the same milkweed that poisons the monarchs also offers a very cozy home for the butterflies, making them either late or no-shows for their annual migration pattern. Most monarchs that are infected with OE will not make it to their destination in central Mexico. It becomes a vicious cycle: the monarchs fail to leave for migration, hence failing to return to look for new milkweed, and instead continue to live in the old infected milkweed that never dies, all while OE continues to thrive.
Because they eat nothing else, monarch numbers have been on the steady decline. This year alone, there was a 27% decrease in monarch numbers compared to the year before. In addition to loss of habitat, the milkweed issue has largely contributed to the species 90% population reduction in the last two decades.
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| Dwindling numbers in the Monarch population have led researchers to study them closer than ever before. (Monarchwatch.org) |
An Uninvited Player for the Kite
In an article from the New York Times, the snail kite finds a new, accidental advantage. A study posted by The Ecological Society of America published last year discusses how a new invasive species of snails is actually helping to aid the resurgence of snail kite populations.
The native apple snail (Pomacea paludosa) that the snail kite dines on, is typically found in the wetland areas like the Florida everglades. However, a larger, non-native version of the snail (Pomacea maculata) became established in South Florida by the end of the breeding season in 2005, and has since spread, becoming a serious invasive species.
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| a, Snail kites are dietary specialists that have morphological traits, particularly bill size and shape, that have adapted to extracting apple snails from their shells. b, The exotic apple snail (P. maculata; right) is a novel prey21 for snail kites, because it is much larger than the native congener (P. paludosa; left), leading to implications for foraging and demography17,19. c, The invasion first occurred in Lake Tohopekaliga, where P. maculata had become established by the 2005 breeding season (orange). By 2009, P. maculata had established in several wetlands (red). Snail kite breeding closely tracked the invasion sequence, where bars show changes in the proportion of nests over time with the invasion (pre-invasion 2003, 2003–2004; initial invasion 2005, 2005–2008; post-invasion 2009, 2009–2012). Annual averages are shown, n = 1,778 nests. Test for change in the proportions of nests across regions over time: F 4,45 = 13.1, P < 0.0001. d, Snail kites do feed on the much larger exotic snails. The relative frequencies of snail sizes consumed by snail kites in 2013–2014 (n = 903) are shown, taken from snail shells collected at foraging perches throughout the range. |
The presence of these non-native snails has had a drastic influence on the kite. First, the larger size of P. maculata made it easier for fledglings to get to the snail meat, causing an increase in young bird survival. Second, biologists also found that the invasive species presence was directly correlated to new generations with longer bills and larger body sizes.
"The potential for an invasive prey to elicit such a rapid response from a long-lived native predator is remarkable...These results illustrate that long-lived, top predators can rapidly respond to invasive species through phenotypic plasticity. Phenotypic plasticity may prove to be crucial to imperiled species, allowing them to rapidly respond as their environment changes," C. Cattau, et al (2016).
Since the invasive snails take-over, the population of the snail kite has nearly tripled, to over 2,000 in 2017. This dramatic population increase is a welcome change for the endangered bird. However, will it be enough to kick start the species back into strong numbers? Time will tell. There are many difficulties with an endangered species being dependent on an invasive species.
One specific challenges lies in the obvious: an invasive species affects more than just one group. The Everglades are an intricately, complicated network of interdependent species. Introducing even just one single new component can irrevocably damage some of those networks. So we are left with a dilemma: is a potentially threatening species worth salvaging a nearly-extinct one?
Hope for the Monarchs
In a 2015 study published by Royal Society Publishing, it was found that monarchs in the southern U.S., neglecting their typical migration patterns, were five to nine times more likely to be infected it OE. The parasite is striking the butterflies at a particularly susceptible time, with their population being closely evaluated by U.S. Fish and Wildlife as falling under the Endangered Species Act.
Fortunately, aid for the monarchs can be fulfilled by scientists and citizens alike. In the previously mentioned Science magazine article, Karen Oberhauser, a conservation biologist at the University of Minnesota, stated part of the fix is quite simple.
"Nearly all tropical milkweed in the southern United States is in gardens, Oberhauser says. So if everyone who planted it to help the butterflies can be convinced to replace it with a native milkweed specie - or at least cut the plant back every few weeks during the winter - they could quickly put a stop to the destructive winter-breeding trend."
The Monarch Joint Venture has an updated yearly plan in place that it claims anyone can be a part of. It's primary focus is to promote planting native milkweed and research efforts as well as educating more public agencies on conservation efforts.
The fate of these magnificent insects is in the hands of the people. With easier than ever and convenient options to switch from harmful milkweed plants to acceptable milkweed, we can assist in the rehabilitation of monarch population numbers.
Why we Should Care
It's no secret that animals and insects alike are up against the odds with global climate change, natural disasters, habitat loss, and other factors. It's becoming increasingly important to study and understand the changes these species are going through. Without understanding them, we pose to lose them.
That may not seem like a big deal right now; you've probably never even seen a snail kite. However, keep in mind that intricate nature of the ecosystem we talked about earlier. The loss of just one species could completely change the survival of hundreds of others. You may be indifferent to never seeing a snail kite or a monarch butterfly again, but you may find indifference difficult when it affects the vegetables on your table, or the lack of wildlife you see on your next hike.
These ecosystems are fragile, and they are facing more challenges than ever before. If we can't understand how they work, we will lose them.
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