Climate Relicts: What Iowa Can Learn from Nature's Population Leftovers

            As a lifelong city-dweller, I came to Grinnell expecting that Iowa’s plant life (aside from all the corn) would consist mostly of prairie. While my first two years here did little to broaden my horizons – the “Grinnell Bubble” is very much a thing – in the past few weeks, I’ve seen both cacti (specifically, the prickly pear, Opuntia humifusa) and pine trees (Pinus strobus) all without going much more than an hour from campus. While they might seem unusual, these plant populations – the former in the Eddyville Sand Dunes and the latter at the aptly-named Pine Lake – are just two examples of what are known as relict populations, fragmented leftovers from a time when the Iowan climate –and therefore its plant communities – scarcely resembled today’s temperate prairie. While scientists have long viewed this type of population, rather intuitively, as a way of peering into the climates of the past, a review by Hampe and Jump (2011) titled “Climate Relicts: Past, Present, and Future” takes a look at past research to make a compelling case that these populations might also be able to tell us a lot about what climate change bodes for our botanical future.

            The gist of the argument that Hampe and Jump make in their paper is that we have a lot to gain if we understand relicts – like the cacti in the Eddyville dunes or the pines of Pine Lake – as populations existing near the edge of their climatic tolerance, and broaden our view of the factors that shape the boundaries of these populations. The authors believe that we should pay more attention to the factors that allow relicts to persist, both external (such as the temperature buffering from ice caves that keeps algific talus slopes cooler than their surroundings) and within the populations themselves (such as the deep roots or other adaptations that help plants survive climate stress). By looking into these oft-ignored factors, we might be able to glean some insight about what will happen to populations – both relicts and otherwise – in the shifting climate conditions that await us as the result of climate change.

            While contemporary views of relicts tend to fixate on things like temperature, Hampe and Jump remind us that we also need to consider how these isolated populations are inhibited or encouraged by the other organisms they share their habitats with. The authors point out that, particularly for populations already under the strains caused by temperature or precipitation level, things like competition or predation can easily limit a population’s size, and that, in fact, relicts can arise as much from an area’s lack of these antagonists as from the climate conditions themselves. On the other hand, some species rely on mutualists, such as pollinators or soil fungi, in order to persist, which can further complicate relict dynamics. Eilers and Roosa (1994), in their list of species commonly found as relicts on algific talus slopes, include the showy lady slipper (Cypripedium reginae). Given the shape of this orchid’s flowers, it has evolved for pollination by specific insects – are these present all across Iowa, or are their own populations more fragmented? Nekola (2002), on a broader note, describes these talus slopes as possessing a “dense bryophyte cover that supports large populations of pteridophytes”, or, in layman’s terms, mosses and related plants that support ferns and their relatives. To what extent does this facilitation influence relict boundaries? This seems to be exactly the type of question that Hampe and Jump suggest needs more research – on the biotic factors that interact with climate relicts.

            Existing research within Iowa has confirmed at least one of the article’s other conclusions: that fragmented, isolated populations experience a loss of genetic diversity that may make it harder for them to adapt as the climate – in Iowa and elsewhere – continues to shift. Shea and Furnier (2002) found that, among relict populations of balsam fir (Abies balsamea) located in the algific talus slopes of northeastern Iowa, genetic diversity was significantly lower than in populations in the center of the species’ range. Hampe and Jump themselves acknowledge that the isolation and small population of relicts has “usually resulted in genetic depauperation” but their suggestions as to how a species can adapt to these conditions present an exciting new area for potential research. Hampe and Jump cite studies that show that relict populations deal with these reproductive consequences with adaptations that promote “reproductive insurance (e.g. self-compatibility, great fecundity) and the connectivity of potential mates (e.g. active mate-location behavior, directional pollen flow)”(Hampe and Jump, 2011). Do the relict plants of Iowa, such as the balsam firs, disproportionately display these characteristics? If so, is it because species with these traits are more likely to persist as relicts, or do individuals within these populations evolve these features over time in the face of reproductive challenges (i.e. intraspecific variation)?

            Looking at the strategies that Hampe and Jump suggest for broadening our perspectives on relict populations, one can see many opportunities for new research on the relicts of Iowa. Despite the wide variety of sources that the authors draw on for their review, they notice that “a large fraction of studies have been performed in mountain ranges” – most likely due to the fact that the topography of these areas, as they note in their article, helps create the kind of microclimate well-suited for relicts. However, even a place like Iowa – stereotyped as a homogenous place full of corn, prairie, and very little else – is home to a surprising array of relict species, often at the southern termini of their ranges, as in the case of P. strobus. Research in Iowa, then, would be useful not just in the ways it could provide perspectives on biotic factors and other under-researched ecological aspects of relicts, but also in telling us more about how relicts outside of mountain ecosystems function. With the global average temperature rising by the year, and other aspects of our climate changing as well, we need now as much as ever to explore how mechanisms of adaptation and extinction work – and the relicts of Iowa are the perfect study site to teach us.

Works Cited

Eilers, L., and Roosa, D. (1994). The Vascular Plants of Iowa. Retrieved from http://uipress.lib.uiowa.edu/vpi/default.aspx .

Hampe, A., and Jump, A.S. (2011). Climate relicts: past, present, future. Annual Review of Ecology, Evolution, and Systematics, 42, 313-333.

Nekola, J.C. (1999). Paleorefugia and neorefugia: the influence of colonization history on community pattern and process. Ecology, 80(8), 2459-2473.

Shea, K.L., and Furnier, G.R. (2002). Genetic variation and population structure in central and isolated populations of balsam fir, Abies balsamea (pinaceae). American Journal of Botany, 89(5), 783-791.