Research

1. Climate-change effects on plants and pollinators

Climate change constitutes a vast, uncontrolled experiment with the world’s ecosystems. Warming is causing the timing (phenology) of flowering and insect activity to get earlier, reducing mountain snowpack, and intensifying summer droughts. However, we still don’t know much about the consequences of these changes for plant and pollinator populations.

In the past, I have studied the possibility that climate change might disrupt temporal synchrony between plants and pollinating insects (Forrest & Thomson 2010, Am. J. Bot.; Forrest & Thomson 2011, Ecol. Monogr.). More recently, I’ve begun to think that other aspects of climate change may pose a greater threat to plant–pollinator interactions in the ecosystems I study (see discussion in Forrest 2015, Oikos). My lab is now investigating the consequences of warmer summers (see Forrest & Chisholm 2017, Ecology), variable springtime temperatures and snowpack reductions for bee survival and fitness.

Cavity-nesting solitary bees (mainly in the family Megachilidae) are my preferred study system for this work. They are important pollinators of wildflowers and certain crops, and–conveniently–they are willing to nest in artificial structures (“trap-nests“) that allow standardization, monitoring, and experimental manipulation. Trap-nests consist of holes drilled in wood and lined with translucent, removable straws that let a researcher monitor nesting progress. To learn how to build a trap-nest, visit the USDA Bee Lab’s How to Build a Nesting Block site.

2. Bees on farms

With Neal Williams (UC Davis), I have looked at why certain bee species thrive on California farms and why others are absent or rare. Certain life-history traits, notably those related to nesting biology, are good predictors of persistence in agricultural settings (Forrest et al. 2015, J. Appl. Ecol.), but experimental tests of the importance of nesting habitat remain to be conducted.

Our lab has now begun more local (Ottawa- and Montreal-area) work on bee communities in agro-ecosystems. Two current graduate students (Jessica Guezen and Gail MacInnis) are independently investigating how floral resources in agricultural landscapes influence bee communities, and how the foraging behaviours represented in these bee communities in turn determine crop pollination.

3. Life-history strategies of solitary bees

Several solitary bee species display what appears to be a bet-hedging life-history strategy, with cohort emergence split among two or more years–a trait that should confer resilience to environmental variation. We are interested in better understanding the distribution (geographic, ecological, phylogenetic) and adaptive value of such life-history traits, with the goal of better predicting which taxa and habitats will be most vulnerable to future environmental change.

 4. Functional significance of floral traits

For many plants, sex depends on getting animal pollinators to visit flowers and move pollen from anthers to stigmas. We are interested in the various traits plants have evolved to achieve these ends.

One of our study systems is the plant genus Mertensia, which exhibits pronounced inter- and intraspecific variation in style length (Forrest et al. 2011, Ann. Bot.), the adaptive significance of which remains elusive. We are also investigating the adaptive value of floral orientation (pendent, to varying degrees) in this genus.

Artificial “flowers”, which can be designed to isolate the effects of particular floral variables, are useful tools for understanding the functional roles of floral traits. For example, we have used artificial flowers in a controlled flight-cage setting with captive bees to study the effect of background complexity on colour preference of bumble bees (Forrest & Thomson 2009, Naturwissenschaften) and the potential for floral symmetry to affect the consistency of pollinator entry angles (Culbert & Forrest 2016, J. Poll. Ecol.).

5. Parasites of solitary bees

Cavity-nesting bees are attacked by a variety of brood parasites (or kleptoparasites), of which the most abundant at our field sites are sapygid wasps (pictured below, middle). These wasps inflict substantial mortality on bee populations, but not all bees are equally susceptible to parasite attack (see Spear et al. 2016, Am. Nat.). My students and I are studying the factors influencing parasitism rates in cavity-nesting bees (see Forrest & Chisholm 2017, Ecology) and investigating how selection imposed by brood parasites interacts with selection imposed by floral resources and the abiotic environment.

 6. Selection and constraint in the evolution of flowering phenology

I use simulation modelling to look at how reproductive phenology responds to different kinds of selection. For example, certain aspects of bumble bee foraging behaviour (specifically, positive frequency-dependence and avoidance of unfamiliar flowers) can select against early flowering in a plant population (Forrest & Thomson 2009, Proc. R. Soc. B). On the other hand, sexual selection can favour early-flowering individuals (Forrest 2014, Am. Nat.).

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