1. Climate-change effects on plants and pollinators

Climate change constitutes a vast, uncontrolled experiment with the world’s ecosystems. Warming is changing the timing (phenology) of flowering and insect activity, reducing snowpack in high-altitude and high-latitude regions, and intensifying summer droughts. 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.; see also my 2015 Oikos Forum/review piece on this topic). Former MSc student Gabriel Gauthier used our lab’s long(ish)-term observations of solitary bee populations to evaluate the extent to which variation in synchrony matters for bee reproduction (manuscript in preparation). My lab has also been investigating the consequences of warmer summers (see Forrest & Chisholm 2017, Ecology) for bee survival and fitness, and the potential for solitary bee populations to shift their ranges upward or poleward as the warming climate requires. This work is funded primarily by NSERC, with help from RMBL.

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

Despite the growing climate crisis, land-use change (specifically, conversion of natural habitat to agriculture) so far remains the #1 cause of biodiversity loss globally. There is a certain dark irony in this, because much of our food production depends, directly or indirectly, on biodiversity—including a diverse range of wild pollinators.

My lab studies the bee communities of agricultural ecosystems (agro-ecosystems) in the Ottawa–Montreal area—how they are affected by landscape features such as flower availability through time (former MSc student Jessica Guezen) and presence of nesting habitat (PhD student Cécile Antoine; see also Forrest et al. 2015, J. Appl. Ecol.), and also how these wild bee communities affect crop yield (former PhD student Gail MacInnis; see MacInnis & Forrest 2019, J. Appl. Ecol.; MacInnis & Forrest 2020, Agr. Ecosyst. Env.). This work is funded by an Ontario ERA.

3. Pollen specialization by solitary bees

Like many other plant-feeding insects, numerous bee species are dietary specialists (oligoleges) that collect pollen from only a subset of the flowering species available in their environment. Evolutionary biologists have recognized for a long time that the risks associated with specialization (surely it makes organisms more vulnerable to extinction?) must come with compensatory benefits (greater efficiency in resource use, perhaps?)—although it has often been challenging to identify those hypothetical benefits.

Among solitary bees, certain plant taxa seem to have been popular hosts on which to specialize, in that multiple bee lineages contain species that specialize on these plant taxa (indicating repeated evolution of specialization on these taxa). But why? We are investigating a couple of hypotheses…

So far, most of our attention has focused on the sunflower family (Asteraceae), the pollen of which seems to be toxic, or at least “low-quality” (we don’t yet know why), for bees that aren’t specialists on this family (see e.g. McAulay & Forrest 2019, Arthropod-Plant Interactions). One of the benefits of specializing on this seemingly poor diet could be that it deters parasites, a major source of mortality for many bee species. Our studies on mason bees in Colorado support this idea (see Spear et al. 2016, Am. Nat.)…. but it’s probably not the only explanation. Asteraceae flowers are also abundant in many habitats, they produce copious amounts of pollen, and the family is species-rich; these factors may have also played an important role in the repeated evolution of specialization on this family.

Clearly, we need to study more than just this one plant family to arrive at a general explanation for bee specialization, and we do have plans to investigate this question more broadly. But one has to start somewhere!

This work is funded by NSERC.

4. Functional significance of floral traits, including pollen defences

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. For example, we have investigated the adaptive significance of style length and floral orientation in Mertensia (Forrest et al. 2011, Ann. Bot.; Lin & Forrest 2019, J. Plant Ecol.) and of pollen colour (yellow to dark red) in Erythronium (Austen et al. 2018, Ecology).

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; Rivest et al. 2017, Evol. Ecol.) and the potential for floral symmetry to affect the consistency of pollinator entry angles (Culbert & Forrest 2016, J. Poll. Ecol.).

More recently (and in relation to the topic of pollen specialization by bees), the lab has become interested in pollen traits. Pollen grains are sometimes spiky, sometimes oily and smelly, sometimes bound together by viscin threads… but pollen also isn’t the easiest substance to study (individual grains are tiny and hard to collect [if you’re not a bee]; it’s only produced during a brief period of a plant’s life and not necessarily by all individuals), so the functional significance of these traits remains largely mysterious. PhD student Sébastien Rivest has written a Perspectives article (Rivest & Forrest 2020, New Phyt.) reviewing the evidence for a few different hypotheses about why pollen often seems to be chemically defended, but the experimental work is still in its early stages.

5. Selection and constraint in the evolution of flowering phenology

In the past, I have used 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.). A few years ago, colleagues and I (led by post-doc Dr. Emily Austen) published our thoughts on why natural selection so often appears to favour early-flowering plants (Austen et al. 2017, New Phyt.). My lab isn’t actively working on this topic at the moment, but it remains a subject of interest.