Drawing on my work in evolutionary ecology, wilderness ethics, and machine learning, I reflected on the tension between our desire to intervene and our limited ability to forecast long-term ecological outcomes. Using examples like the Chernobyl exclusion zone—where many species are thriving in the absence of people despite nuclear contamination—I argued that ecological recovery is often less about precision intervention and more about restraint. We discussed how machine learning can help us simulate alternative futures and understand potential tradeoffs, but that ultimately, the most powerful conservation tool may be humility. More wilderness, not more control, might be the best way to meet the uncertainties ahead.

Listen to the episode here or wherever you get your podcasts.

The study:

One of the most consistent findings arising from 20 years of study in our lab is that wood frogs seem to adapt to life in cold, dark ponds. In general, cold-blooded animals like reptiles and amphibians are not suited for the cold and function much better in warmer conditions. So, wood frogs that live in colder ponds should have a harder time competing against their neighbors in warmer ponds.

In response, cold-pond wood frogs seem to have developed adaptations that level the playing field. In separate experiments, we’ve found that wood frog tadpoles in cold-ponds tend to seek out warmer water (like in sunflecks) and have lower tolerance to extremely warm temperatures. Most importantly, they can mature faster as eggs and larvae.

But I’ve always struggled with a lingering question: if cold pond frogs have adapted these beneficial adaptation to compete with warm-pond frogs, what is keeping those genes out of the warm-ponds? Shouldn’t cold-pond genes in a warm pond mean double the benefits? One would expect the extrinsic environmental influence and the intrinsically elevated growth rates to produce super tadpoles that metamorphose and leave the ponds long before all the others.

Kaija, who was an undergrad in the lab at the time, decide to tackle that question for her senior thesis.

We hypothesized that there might be a cost to developing too quickly. Studies in fish suggested that the trade-off could be between development and performance. The idea is that, like building Ikea furniture, if you build the tissue of a tadpole too quickly, the price is loss of performance.

So we collected eggs from 10 frog ponds that spanned the gradient from sunny and warm to dark and cold. We split clutches across two incubators that we set to bracket the warmest and coldest of the ponds.

Then we played parents to 400 tadpoles, feeding and changing water in 400 jars two to three times a week.

We reared the tadpoles to an appropriate age (Gosner stage 35ish). Those in the warm incubator developed about 68% faster than those in the cold incubator. In addition to our lab-reared tadpoles, we also captured tadpoles from the same ponds in the wild as a comparison. Development rates in the lab perfectly bounded those in the wild.

Once they reached an appropriate size, we put them to the test. We simulated a predator attack by a dragon fly naiad by poking them in the tale. Dragonfly naiads are fast, fierce, tadpole-eating machines and a tadpole’s fast-twitch flight response is a good indicator of their chance of evading their insect hunters. It’s a measure of performance that directly relates to a tadpole’s fitness.

Above the test arenas, we positioned highspeed cameras to capture the tadpoles’ burst responses. We recorded 1245 trials, to be exact—way more than we ever wanted to track by hand. Fortunately, Kaija is a wiz at coding; and with a bit of help, she was able to write a Matlab script that could identify the centroid of a tadpole and record its position 60 times per second.

We measured the tadpoles’ speed during the first half second of their burst response and looked for an association with their developmental rates. One complicating factor is that a tadpole’s fin and body shape can influence burst speeds. So, a weak tadpole with a giant fin might have a similar burst speed to a super fit tadpole with a small fin. To account for this, we took photos of each tadpole and ran a separate analysis mapping their morphometry and included body shape into our models.

As we had hypothesized, tadpoles reared at warmer temperatures show much slower burst speed than their genetic half-sibling reared in the cold incubator. We even saw a similar, but weaker effect for the tadpoles that were allowed to develop in their natal ponds. It seems that developing too fast reduces performance.

Thus, it certainly seems that the counter-gradient pattern we see of faster development in cold-pond populations, but not in warm-pond populations, is at least partially driven by the trade-off between development rate and performance.

In fact, it may even be the case that we’ve been viewing the pattern backwards all along. Perhaps instead we should consider if warm-pond populations have developed adaptively slower development rates to avoid the performance cost. This especially makes sense given the range of wood frogs. Our populations are at the warm, southern end of the range. Maybe this tradeoff is also a factor constraining wood frogs to the cold north of the continent?

If warm weather and faster development are a real liability for wood frogs, it is only going to get worse in the future. We know from another recent study that our ponds have been warming quickly, especially during the late spring and early summer months. But climate change is also causing snow to fall later in the winter forcing frogs to breed later. The net result is that wood frogs may be forced to develop fast intrinsic developmental rates in response to a contracting developmental window, while at the same time, extrinsic forces drive development even faster. That’s a double whammy in the trade-off with performance. And might lead to too many “Ikea furniture mistakes” at the cellular level.

As a separate part of this study, we also measured metabolic rates in out tadpoles in hopes of understanding the relationship between developmental rates, performance, and cellular respiration. I’m in the process of analyzing those data, so stay tuned for more!

Here’s my talk from the conference, “Evolution of Intrinsic Rates: Can adaptation counteract environmental change?“:

But it turns out, when you take the time to look closely, evolution is taking place all around us, fast enough for us to see and measure. What’s more, evolution may even happen faster around us since we humans tend to create novel and often extreme selection environments that encroach into natural habitats (or entirely new habitats for those species that hitchhike into citeis with us). Johnson and Munshi-South (2017) reviewed the growing list of studies uncovering rapid evolution of wildlife in response to urbanization.

I showed the article to my partner (Baylaart.com) who used it as a theme for her most recent piece which is comprised of organisms subject to contemporary urban adaptations. Both the article and the painting are exceptional work that I’ll walk through below.

When faced with new environmental challenges, populations of organisms are faced with two options: move or adapt. (The third, extreme alternative is extinction). Urban wildlife populations are either residual populations that existed prior to urban development or new populations that colonized after a city emerged.

A classic example of urban adaptation is industrial melanism in the peppered moth (Biston bitularia) (Kettlewell 1955, 1958). As soot poured out of cities during the industrial revolution, the light colored polymorphism of the peppered moth offered poorer camouflage than the black, soot-colored morph. As a consequence, the dark morph came to dominate urban populations. As industry cleaned up its act, the trend reversed.

We can see the effects of urbanization in modern cities, today. White-footed mice (Peromycus leucopus), a North American native, in urban settings are marked by much less genetic variation, and therefore, lower evolutionary potential (Munshi-South et al. 2016). On the flip-side, this reduced variation could be the result of selection sweeping all unadapted alleles from the population, leaving a more genetically homogenous population as a result of the evolutionary process. Even animals that look unchanged may have evolved subtle adaptations. For instance, blackbirds (Turdus merula) in cities exhibit a molecular level difference in a gene associated with harm avoidance behavior compared to their natural brethren (Mueller et al. 2013).

Some species have adapted so well to urbanization, that they are almost synonymous with cities world-wide. For instance, the German cockroach (Blatella germanica), Rock dove (Columba livia), and Norway rat are veritable mascots of cities. Urban roaches and rats have evolved resistance to pesticides (Booth et al. 2011; Rost et al. 2009), and roaches in cities have even evolved an aversion to glucose in response to selection by sugar-baited traps (Wada-Katsumata et al. 2013). Rock doves in the cities have evolved defenses, not to human extermination attempts, but to predation by city-dwelling falcons (Palleroni et al. 2005).

Some populations precede city creation. Red-backed salamanders (Plethodon cinerus) in Montreal, Canada managed to persist as the city was constructed around them, but their populations have been isolated genetically, resulting in low variation (Noel & Lapointe, 2010). Across the Atlantic fire salamanders (Salamandra salamandra) also had a city (Oviedo, Spain) built atop their population starting over a millennia ago and managed to persist despite severe restriction in gene flow (Lourenco et al. 2017). Animals don’t need hundreds of years to adapt to new development, though. Water dragons (Intellagama lesueurii) inhabiting newly established city parks built as recently as 2001 in Brisbane, Australia have developed genetic difference in body shape and total size (Littleford-Colquhoun et al. 2017). Similarly, a small population of dark-eyed juncos (Junco hyemalis) established in the 1980s have been thoroughly studied (due largely to their location on the UC San Diego campus) and found to have evolved shorter wings, shorter tails, and alternate plumage pattern in just the past few decades (Rasner et al. 2004; Yeh 2007).

Other species, like the common wall lizard (Podarcus muralis) and striped mouse (Apodemus agrarius), seem to have been able to adapt to the development of Trier city in Germany (for lizards (Beninde et al. 2016)) and Warsaw, Polans (for mice (Gortat et al. 2014)) and now disperse through the city architecture in a similar way to their natural environment. Cityscapes can offer very similar (although much more angular) habitat to an organism’s natural habitat. For instance, Anoles (Anolis cristatellus) perch on the vertical trunks of trees in the forest. The flat walls of building in Puerto Rico offer a similar niche; however, artificial walls tend to provide less grips for lizards. In response, urban Anoles have evolved longer limbs and stickier toepads to cling to homes and businesses (Winchell et al. 2016).

Small animals are not the only wildlife subject to urban impacts. The movement of many large mammals, such as bobcats (Lynx rufus) (Serieys et al. 2014), are restricted by roadways, despite our best efforts to promote connectivity. In some cases, large and mobile animals are able to break into the new habitats afforded by cities. Red foxes (Vulpes vulpes) colonized the city of Zurich, Switzerland less than two decades ago and in that time their urban populations have exploded (Wandeler et al. 2003). While the original urban populations were likely established by just a few intrepid foxes, now that the urbanite populations are large enough, they have established genetic connectivity with their rural counterparts, essentially extending the larger population’s range to include the city.

In addition to landscape alterations that reduce gene flow and incur selection, urban settings can actually increase genetic mutation rates (which is ultimately the raw substrate for evolutionary adaptation). As an example, the rate of mutation in herring gulls (Larus argentatus) that nest in a heavily industrialized site in Ontario is double their less urban counterparts likely due to exposure to toxic chemicals in the environment (Yauk & Quinn 1996).

Let’s not forget that animals are not alone in their evolutionary response to urbanization—plants have also demonstrated adaptations to cities. Clover (Trifolium repens) in urban populations have evolved a reduction in cyanogenesis, a process that makes the plant less palatable to herbivores but in trade-off leaves the plant less tolerant of freezing temperatures (Thompson et al. 2016), which makes sense since there aren’t many large grazers wandering city streets and urban settings tend to act as heat islands.

In order to reduce seeds falling on infertile concrete streets and sidewalks, Holy hawksbeard (Crepis sancta) a weed in Montpellier, France have evolved to produce less dispersing seeds (Cheptou et al. 2008). In addition, the urban plants evolved an increase in photosynthesis and larger flowers (Lambrecht et al. 2016). Virginia pepperweed (Lepidium virginicum), is a common weed in many U.S. cities. A study of genetic divergence between urban and rural settings found that urban plants were more closely related than the more geographically proximal rural populations (Yakub & Tiffin 2016). In addition, the city pepperweed had developed a different shape and growing season to rural plants.

It’s clear that almost anywhere you look in cities, wildlife is evolving in response to our presence. This bestows us with a massive responsibility and indebts us to an ethic of conservation, not of species themselves, but to preserve as much unencumbered wild habitat as possible (for instance, as designated Wilderness). Where saving wild space is impossible, we must work on mitigating the effects of our urban infrastructure (for instance).

Literature cited:

Beninde, J., Feldmeier, S., Werner, M., Peroverde, D., Schulte, U., Hochkirch, A., et al. (2016). Cityscape genetics: structural vs. functional connectivity of an urban lizard population. Mol. Ecol. 25, 4984–5000.

Booth, W., Santangelo, R. G., Vargo, E. L., Mukha, D. V., and Schal, C. (2011). Population genetic structure in german cockroaches (blattella germanica): differentiated islands in an agricultural landscape. J. Hered. 102, 175–183.

Cheptou, P.-O., Carrue, O., Rouifed, S., and Cantarel, A. (2008). Rapid evolution of seed dispersal in an urban environment in the weed Crepis sancta. Proc. Natl. Acad. Sci. U. S. A. 105, 3796–3799.

Gortat, T., Rutkowski, R., Gryczyńska, A., Pieniążek, A., Kozakiewicz, A., and Kozakiewicz, M. (2015). Anthropopressure gradients and the population genetic structure of Apodemus agrarius. Conserv. Genet. 16, 649–659.

Johnson, M. T. J., and Munshi-South, J. (2017). Evolution of life in urban environments. Science 358.

Kettlewell, H. B. D. (1955). Selection experiments on industrial melanism in the Lepidoptera. Heredity 9, 323.

Kettlewell, H. B. D. (1958). A survey of the frequencies of Biston betularia (L.) (Lep.) and its melanic forms in Great Britain. Heredity 12, 51.

Lambrecht, S. C., Mahieu, S., and Cheptou, P.-O. (2016). Natural selection on plant physiological traits in an urban environment. Acta Oecol. 77, 67–74.

Littleford-Colquhoun, B. L., Clemente, C., Whiting, M. J., Ortiz-Barrientos, D., and Frère, C. H. (2017). Archipelagos of the Anthropocene: rapid and extensive differentiation of native terrestrial vertebrates in a single metropolis. Mol. Ecol. 26, 2466–2481.

Lourenço, A., Álvarez, D., Wang, I. J., and Velo-Antón, G. (2017). Trapped within the city: integrating demography, time since isolation and population-specific traits to assess the genetic effects of urbanization. Mol. Ecol. 26, 1498–1514.

Mueller, J. C., Partecke, J., Hatchwell, B. J., Gaston, K. J., and Evans, K. L. (2013). Candidate gene polymorphisms for behavioural adaptations during urbanization in blackbirds. Mol. Ecol. 22, 3629–3637.

Munshi-South, J., Zolnik, C. P., and Harris, S. E. (2016). Population genomics of the Anthropocene: urbanization is negatively associated with genome-wide variation in white-footed mouse populations. Evol. Appl. 9, 546–564.

Noël, S., and Lapointe, F.-J. (2010). Urban conservation genetics: Study of a terrestrial salamander in the city. Biol. Conserv. 143, 2823–2831.

Palleroni, A., Miller, C. T., Hauser, M., and Marler, P. (2005). Predation: Prey plumage adaptation against falcon attack. Nature 434, 973–974.

Rasner, C. A., Yeh, P., Eggert, L. S., Hunt, K. E., Woodruff, D. S., and Price, T. D. (2004). Genetic and morphological evolution following a founder event in the dark-eyed junco, Junco hyemalis thurberi. Mol. Ecol. 13, 671–681.

Rost, S., Pelz, H.-J., Menzel, S., MacNicoll, A. D., León, V., Song, K.-J., et al. (2009). Novel mutations in the VKORC1 gene of wild rats and mice–a response to 50 years of selection pressure by warfarin? BMC Genet. 10, 4.

Serieys, L. E. K., Lea, A., Pollinger, J. P., Riley, S. P. D., and Wayne, R. K. (2015). Disease and freeways drive genetic change in urban bobcat populations. Evol. Appl. 8, 75–92.

Thompson, K. A., Renaudin, M., and Johnson, M. T. J. (2016). Urbanization drives the evolution of parallel clines in plant populations. Proc. Biol. Sci. 283. doi:10.1098/rspb.2016.2180.

Wada-Katsumata, A., Silverman, J., and Schal, C. (2013). Changes in taste neurons support the emergence of an adaptive behavior in cockroaches. Science 340, 972–975.

Wandeler, P., Funk, S. M., Largiadèr, C. R., Gloor, S., and Breitenmoser, U. (2003). The city-fox phenomenon: genetic consequences of a recent colonization of urban habitat. Mol. Ecol. 12, 647–656.

Winchell, K. M., Reynolds, R. G., Prado-Irwin, S. R., Puente-Rolón, A. R., and Revell, L. J. (2016). Phenotypic shifts in urban areas in the tropical lizard Anolis cristatellus. Evolution 70, 1009–1022.

Yakub, M., and Tiffin, P. (2017). Living in the city: urban environments shape the evolution of a native annual plant. Glob. Chang. Biol. 23, 2082–2089.

Yauk, C. L., and Quinn, J. S. (1996). Multilocus DNA fingerprinting reveals high rate of heritable genetic mutation in herring gulls nesting in an industrialized urban site. Proc. Natl. Acad. Sci. U. S. A. 93, 12137–12141.

Yeh, P. J. (2004). Rapid evolution of a sexually selected trait following population establishment in a novel habitat. Evolution 58, 166–174.

Overview:

Isle Royale is an island in Lake Superior that is designated as a Wilderness Area and managed by the National Park Service. In the 20th century, wolves and moose migrated to the island and their dynamic spurred one of the longest predator-prey studies in history. Now, the wolf population has dropped to 2 and the Park Service is planning a major intervention that will install an entirely new, synthetic population of wolves on the island. This plan is the result of myopic research perspective and disregard for eco-evolutionary dynamics. It is bad policy and even worse science. Here’s why:

Background:

Isle Royal is a smallish-island (just over 200 square miles) that sits about 8 miles from the north shore of Lake Superior. (Although it is small, it is large enough to host its own internal lake with an island, making it, as upper-midwesterners are fond of point out, the largest island on the largest lake on the largest island on the largest lake in the world.) The Isle and its many tiny satellite islands became a National Park in 1940 and were designated as a federal Wilderness Area in 1976.

Because the island is small and a long swim from the mainland, large fauna populations have been inconsistent denizens, historically. Moose first arrived on the island in the early 1900s. Wolves followed the moose in the 1940s, adding two major trophic levels to the island ecosystem. The complex predator-prey interactions became one of the classic test cases of ecological theory (see Peterson et al. 1984; McLaren & Peterson 1994).

Over the decades, the wolf and moose populations have demonstrated a standard predator-prey oscillation, with the wolves generally bouncing around about 20 individuals, but reaching a population maximum of 50 individuals in the 1980.

However, Isle Royale is a small place. Small islands are more susceptible to tipping points on the roller-coaster of demographic stochasticity. It’s kind of like drunkenly walking along the centerline of a bridge versus drunkenly walking a tightrope. If you stumble off course too far on the bridge, you have the latitude to recover and get back on course. Too big a waiver on a tightrope and you’re done for. The small size and isolation of Isle Royale makes it a tight rope for large predators. Like all oscillatory ecological patterns, what goes up eventually comes down, and in the last decade or so, the wolf population has declined in a mirror-like inversion of the population boom in the 1980s. As of this year, there are only two wolves left. As per the dynamics of island-biogeography, the natural course looks like the rein of the wolf will eclipse on the island, probably followed by a boom and eventually extirpation of moose, and the island will continue along as it did for the many decades prior to the most recent immigration events. That is, until the next colonists arrive, as has happened multiple times in the past. Coyotes immigrated and blinked out in 50 years in the early to mid-1900s. At times, lynx and caribou both made the pilgrimage to the island and subsequently slipped off the tightrope.

The issue:

Now, the National Park Service has released an Environmental Impact Statement (EIS) for a plan to install a new populations of wolves on the island (available here). If you are unfamiliar with the NEPA process, here’s how it works: When a land management agency like the National Park Service wants to embark on a project that might run counter to its mandate and/or result in large impacts, they are required to vet all potential options, usually as an EIS, and ask for the public’s comments on the plan. After the revision process, they make a final decision to enact one of those potential options, the “preferred alternative.”

Since 99% of  Isle Royale Park is a designated Wilderness, “where the earth and its community of life are untrammeled by man” and “generally appears to have been affected primarily by the forces of nature, with the imprint of man’s work substantially unnoticeable” (Wilderness Act, 1964), shipping in a boatload of wolves to manipulate the ecosystem required an EIS.

As a scientist and especially as an ecologist, I tend to view Wilderness Areas as our most critical ‘controls’ or ‘baselines’ for science to contrast other areas where human impact alters systems. Though every system is touched by human impact to some extent, there is huge value in preserving the least impacted places in an unmanipulated state. As an analogy, a blemished diamond might be worth a little less than a perfect diamond, but that doesn’t reduce it to equal value with a lump of coal.

But, not all scientists think that way.

To introduce or not to introduce:

The push to introduce wolves to Isle Royale has been championed primarily by two researchers at Michigan Tech, John Vucetich and Rolf Peterson, whose careers are rooted in the Isle’s wolf-moose study.

I first heard about this proposal when Vucetich gave a presentation at the Sigurd Olsen Environmental Institute. At the time, it wasn’t the science that bothered me about the presentation–it was the patent misrepresentation and obvious straw-man Vucetich employed to characterize the intention of the Wilderness Act. Since then, these researchers have made major pushes in film (and this one) and popular press to portray wolves as an ever-present and integral part of the Isle Royale ecosystem, and pit the “health” of the ecosystem against what they believe is an outdated philosophy of conservation.

Essentially, their argument is that since climate change impacts the whole globe, no wilderness is really free of human manipulation, so we should be free to further manipulate it to our own design. They explicitly argue for “new visions for the meaning of wilderness,” with their preferred vision being “a place where concern for ecosystem health is paramount, even if human action is required to maintain it” (from here).

Intentionally or not, their use of relativistic “ecosystem health” rhetoric and attempts to stretch the ‘wilderness myth’ concept into their own application has thoroughly muddied the debate.

And it’s resulted in a lot of public confusion on the topic. For instance, here’s one comment I pulled from the public response in the EIS:

I have visited Isle Royale twice and it remains one of my favorite places in the world. The wolves and the moose have become a part of the island and that is a good thing. Wolves and moose aren’t faring well on the mainland due to politics ignorance and climate change. Isle Royale remains a unique microcosm where we can still observe and study this ancient predator-prey relationship. In a world where species are becoming extinct on a daily basis, this rare relationship has endured and that should be given a lot of weight when making the decision of what to do about the wolf-moose problem on Isle Royale. Please use common sense and act sooner rather than when it is too late.

First off, it’s not an ancient relationship (it’s only been going on for 60 years on the island), and it’s not a rare relationship (wolves eat moose all over the continent all the time). What makes it “rare” is the fact that it happens without human intervention (at least until NPS takes control of the population) on an isolated island with researchers tracking every move.

This person’s comment shows that opinions on the wolf issue are completely colored by human perception: i.e. anything that happened before your lifetime is “ancient,” anything that looks the way it is when you first saw it is “natural,” if you’ve only heard about something in one place, it must be “rare,” etc. The most pernicious perception is that the only species that are worth concerning ourselves with are the big ones with faces that you can relate to (after all, amphibian populations fluctuate on and off in ponds all over the upper midwest following the exact biogeographic pattern as the wolves of Isle Royle, but I’ve yet to see an outrage).

Even the main proponents of wolf introduction, Vucetich et al. and the National Parks Conservation Association invoke the myth that a “sustainable” wolf population is critical to the island’s “health.” Considering that wolves only appeared on the island within a human lifetime and probably blinked on and off the island historically, wolves are only an ephemeral component of this dynamic ecosystem. They never have been “sustainable,” and if ecosystem “health” hinges on the presence of wolves, the island has always been naturally unhealthy.

The rhetoric of “healthy” ecosystems is useless in science, because its meaning is entirely relative. Rolf Peterson, the researcher who initiated the moose-wolf study in the 70s, states that, “There’s a mythical belief that Isle Royale has been working well because we kept our hands off it; my opinion is, it worked well because there were wolves there” (from here). You can only consider a wolf-inhabited Isle Royale as “healthy” if you define a “healthy” ecosystem as one that looks the same way it did when you started your research plan. The real myth is conflating wolf presence with Isle Royale’s natural state, and in this case, it seems a personal mythology crafted to shore the legacy of Peterson’s research project.

The Park’s plan:

The preferred action of NPS is to install 20-30 wolves on the island over the next 3 years, and if those don’t take, to continue introducing for 2 more years.

Originally, the proponents of airdropping new wolves onto the Isle proposed it as genetic “rescue.” But with only two post-breeding age, inbred stock left, there is little chance that new wolves will breed with the two relics. Thus, in reality, this is not a genetic rescue project, it is a genetic replacement project.

So, where do the replacement wolves come from? The EIS suggests that wolves should be sourced from the mainland near the Park, but that many different populations around Lake Superior should be mixed on the island. They also suggest sourcing wolves with experience hunting moose (which are rare in mid-western populations).

Will a new population fair better? The reason wolves lost the plot in the first place was due to the ubiquitous force of natural selection. When faced with strong selection pressure, organisms are faced with three choices: move (not possible on an island), adapt, or disappear. The current wolves were not able to adapt to the ecological scenario they found on the island, so they are disappearing. The NPS knows that new wolves will be even more likely to succumb to selection pressure because they will not be locally adapted. This is why they are planning recurring introductions for a total of up to 5 years. The new population, with lots of diverse genetic material to work with, might be more prone to local adaptation, or it might be more prone to crash because the animals are too locally adapted to their naive system to cope in the new setting.

It might be tempting to think that evolution won’t be a factor considering the short tenure of wolves on the island, but wolf generation times are under 5 years (Mech et al. 2016) which means that they’ve had about 20 generations on the island. We know from the deluge of rapid evolution studies in the past few years that 20 generations is well within the timespan for marked evolution. Similarly, one can expect that moose have been evolving in that time too (Hoy et al. 2018), as have the plants that are browsed by moose, and the small mammals, and the microorganisms that exists in concert… In other words, the entire trophic system has been subject to dynamic eco-evolutionary change that has refined its assemblage and genetic composition. Replacing local wolves with wolves from elsewhere will short-circuit that dynamic process and set a new eco-evolutionary trajectory. Any study that occurs post-introduction will be studying a different eco-evolutionary system, altogether.

Proponents have made the case that occasional genetic influx from the mainland population (when a wolf might cross the ice to the island in cold winters) is part of the natural dynamic, but that climate change has disrupted this process. Leaving aside the fact that much of Isle Royales history was wolf-less long before climate change, reintroducing wolves does not simulate this natural process. In natural migration events, wolves are not randomly selected from a larger pool. The process of migration is a selective sieve that winnows out some potential migrants and selects for others. By high-grading the genetic stock from the mainland based on their own criteria, the Park Service will not be replicating nature, they will be conducting a large-scale, manipulative selection experiment.

The value of non-intervention:

As I mentioned, one of the most critical values of Wildernesses are their role as baselines. This is a point  repeatedly highlighted in the “Strategic Plan for Scientific Research in Isle Royal National Park” (Schlesinger et al. 2009).  The Plan lists as “Unique Attributes of Isle Royale National Park” that it is “An Isolated Location for Baseline Studies”, and “an Ideal Place to Study Fundamental Ecological Concepts” like island-biogeography and predator-prey dynamics.

Isle Royale attracts biogeographers, whose focus is the distribution of life forms as determined by the balance of regional dispersal and local extinction processes (MacArthur and Wilson 1967). Determination of the relative importance of both dispersal and extinction is of central interest to ecologists wishing to explain variability in the species diversity of a given environment and the potential changes brought about by environmental change. As the Strategic Plan states, “the pristine nature of Isle Royale offers an opportunity to examine the potential influence of regime shifts due to natural causes or indirect anthropogenic causes such as climate change.” If we choose a policy of artificially imposing stasis on a naturally dynamic ecosystem we lose that value almost entirely.

On the other hand, if we practice humility and allow natural systems to be dynamic, we can ask a list of interesting questions: What happens if we remove those top trophic levels of moose and wolf? How will that impact the nutrient cycle? How will it impact community dynamics? In what ways will the change in selection pressures drive evolution? Will the eco-evo dynamic play out in predicatable ways based on theory and inference from other archipelagos? What will the post-wolf community composition look like and will it be the same as the pre-wolf community? Etc. etc…

There are endless scientific questions that a wolf-less IR can answer. On the other hand, a replacement wolf population cannot even answer the original question that it is intended to address because such a manipulation cannot be considered a continuation of that community; at best, we can only consider this a manipulative experiment at the price of sacrificing an entire natural ecosystem and ruining an exemplary opportunity to study eco-evo dynamics.

References:

Hoy, S.R., Peterson, R.O., and Vuctich, J.A. 2018. Climate warming is associated with smaller body size and shorter lifespans in moose near their southern range limit. Global Change Biology. DOI: 10.1111/gcb.14015

It might be surprising, but tree canopies can have major impacts on aquatic amphibians. The greater the canopy cover, the less light will reach a ponds surface. Wood frog tadpoles are adapted for rapid development and every small increase in water temp from every small stream of sunlight can make or break a tadpole’s survival. In addition to temperature, the amount of light incident on a pond dictates the amount of algae growth, which in turn dictates the concentration of oxygen in the water. Also, the amount of algae can dictate how much food competition exists between tadpoles, and how bold tadpoles must be to seek out food. In a pond full of predators, being bold can have dire consequences.

More leaves in the canopy also means more evapotranspiration, which in turn means greater water demand from tree roots. As tree suck water out of the ground, the water levels in the pool drops and eventually dries out completely. Amphibians are in a race against time to metamorph before that happens.

So, as you can see, tadpoles and trees have a surprisingly close relationship. All of these compounding factors allow us to tell a lot about wood frog evolution, just by looking up.

The darwin is a great unit if you are interested in long-term macroevolutionary change, but sometimes it falls short for certain questions. For instance, what if we wanted to compare the evolutionary rates of a tree and its insect pest? One limitation of the darwin that Haldane noted was that it doesn’t account for generation times. Over the order of millions of years, it probably is a wash, but if you are interested in short time windows, say 1000 years, generation times matter, especially when comparing a tree with 100 year generation time and an insect that reproduces annually. For this purpose, Philip Gingerich proposed a unit he dubbed the haldane.² The haldane is similar to the darwin, but the rather than directly comparing mean trait values it compares trait values scaled to their standard deviation and rather than measuring time in millions of years, it measures time in generations. Here’s how it looks:

The haldane is good unit for change over time, but what if we are also interested in divergence over space? For instance, what if we are interested in comparing rates of evolutionary change in populations of fish in a river channel? We would expect there to be more divergence in population at the headwaters and the outlet than between populations just a few stream-miles apart, so how can we account for that? Richardson et al. proposed a unit for just this question in 2014.³ They suggested that there is a radius in which we would expect gene flow to disallow divergence. This is the dispersal kernel, depicted in their paper. Within that radius we would be surprised if trait values differed between populations, but outside we might be less surprised. Therefore, they scaled their unit to a distance ratio with that radius. To keep with tradition, they named their unit the wright after Sewall Wright, one of the fathers of population genetics. In their formulation, the difference in trait means is compared as in the darwin, but it is scaled to the pooled standard deviation and the distance ratio.

And this leads me to my current adventure in evolutionary analysis: how to best visualize the pairwise divergence of multiple populations with overlapping dispersal kernels? In my case, I have phenotypic traits for 15 population. I would like to visualize the pair-wise difference in traits with respect to their geographic distance. To further complicate things, I’m not entirely sure what distance to assign for a standard dispersal kernel.

My strongest idea so far has been to display a pair-wise matrix with wright values in the lower triangle and geographic distance in the upper triangle. I ran an ANOVA on trait means by location and used the multiple Tukey HSD post hoc comparison p-values to assign a shading to significant divergence in the lower triangle. In the upper triangle, red shaded values indicate distances less than a 1000m dispersal kernels. The outlined squares in the lower triangle indicate significant divergence within a dispersal kernel, or microgeographic divergence as defined by Richardson et al. 2014. Since I’m not sure what an average dispersal distance might be, I ran the same analysis for 500m, 1000m, and 2500m (only the 1000m analysis is shown). To help illustrate the matrix, I’ve include a nearest neighbor joining spatial plot for each dispersal kernel distance (500m, 1000m, and 2500m).

There is a lot of information digested into this one plot. So I’d be happy to hear any thought on how I could improve it.

¹ Haldane, J.B.S. (1949). Suggestions as to quantitative measurement of rates of evolution. Evolution 3:51–56.

² Gingerich, P.D. (1993). Quantification and comparison of evolutionary rates. American Journal of Science. 293-A, 453-478.

³ Richardson, J.L. et al. (2014). Microgeographic adaptation and the spatial scale of evolution. Trends in Ecology and Evolution. 29(3), 165-176.