Hargreaves lab
Current research interests
Ecology and Evolution of Range Limits
Understanding species’ ranges involves fundamental questions in ecology (how do niches affect habitat use?), evolution (why don't populations at range edges continually adapt to expand the range?), and conservation (how will species' distributions respond to climate change? How important is it to conserve edge vs. central populations?).
Experimental tests of range limit theory
Despite a surge in theory, good experimental tests are surprisingly rare. Since 2010 we have been testing range limit theory out in the wild. Our longest running study system uses the elevational distribution of the herb Rhinanthus minor in Alberta's Rocky Mountains. We've recently started thinking about how range edge theory can help inform conservation of at-risk plants, using Sundial lupine and White trillium. We use demographic surveys and reciprocal transplants across and beyond species' ranges to test many questions, including whether fitness declines toward range limits, whether plants are locally adapted to their home elevations, whether edge populations are best suited to expand the range, and whether different factors control different range limits. We also manipulate abiotic factors (e.g. temperature), and biotic factors (e.g. seed predation, herbivory, pollination) to test how they affect fitness and local adaptation.
Dispersal evolution and range shifts
Dispersal plays a huge role in governing gene flow and adaptive potential within species ranges, how well species maintain small isolated populations (e.g. following habitat fragmentation or at the edge of their ranges), and how quickly species ranges can shift in response to environmental change. We study how dispersal evolves at range edges, particularly at contracting range edges since as warm-edge populations are both the most likely to harbour adaptations needed for a warming world and the most vulnerable to extinction under climate change.
Data synthesis: seeking patterns among the case studies
A consistent theme of our work is to search for general patterns and truths across species and ecosystems. Whereas field experiments are immensely useful in providing strong tests of theory, they are labours of love and generally can only tackle one species in one place at a time. By compiling data from all the studies we can find around the world, we can answer questions like 'how often does...' or 'in which ecosystems does...'. Often we gather the data ourselves, sometimes we use published databases. We've tackled questions like 'Do species interactions limit species ranges more often at low latitudes and elevations? (paper); How often does lack of pollination limit plant ranges? (paper); Do species interactions commonly drive local adaptation? (paper); How often do fitness declines vs dispersal limit species ranges? (paper)
Geographic importance of species interactions
Species interactions, such as competition or herbivory, can sharpen range limits in theoretical models and in some interesting case studies, but their general importance is unclear. Do we need to incorporate them into range shift projection models? Can we predict where interactions matter, or which matter most? A long-standing but poorly tested hypothesis suggests biotic interactions are more important toward low-elevation and latitudes, where biodiversity is highest.
To test this hypothesis Prof Hargreaves' coordinates a network of biologists to conduct replicated, standardized tests of biotic interactions along elevational gradients from the Arctic to Equator (the B.I.G. experiment; photo to the left). We can then test whether interactions are more intense toward the tropics and low elevations, as predicted (results of phase 1 here)
Pollination
Pollination is one the most fascinating interactions between species: complex, varied, quirky and beautiful. Plants, which we often think of as passive, have nevertheless evolved elaborate combinations of floral traits that manipulate animals into couriering their gametes.
Although pollination is a classic example of a mutualism, in which both parties benefit from the interaction, the relationship between flowers and their visitors can also become parasitic, with either animals or plants ‘stealing’ their reward (food or pollination, respectively) without providing one in return. For example, we show that honey bees can, counterintuitively, lower the reproductive success of plants they visit (article), especially in ecosystems without native social bees (article). Given these diverse outcomes, many floral adaptations can be interpreted as either attractants that reel in good pollinators, or deterrents that discourage bad ones. These adaptations, in turn, are responsible for a great deal of the species diversity among flowering plants, one of the most diverse groups on the planet.
We are currently interested in the importance of biotic interactions at large spatial scales, and whether pollination and other mutualisms are as important as antagonistic interactions (e.g. competition) when predicting species' responses to environmental change.
Our research has been generously supported by NSERC, FRQNT, CFI, the Alberta Conservation Association, New Frontiers in Research Fund, Canadian Pollination Initiative (NSERC-CANPOLIN), Calgary Zoo Conservation Research Fund, UBC Biodiversity Research Centre, McGill & Queen's Univ.