Survey
I began a long-term survey of 15 populations of goldenrod in Spring
2015. I demarcated populations at the Koffler Scientific Reserve (KSR),
Ontario, Canada with the criteria that (i) goldenrod (and thusEurosta ) were in distinct patches separated from one another by a
matrix of grass and other forbs, (ii) populations were separated by at
least 50m to ensure relative population isolation (Cronin et al. 2001,
Start and Gilbert 2016), and (iii) populations were broadly distributed
across the entire study site (see map of locations in Fig. S1).
Beginning in 2015 I collected up to 50 galls per population annually
(Table S1). All galls were collected in mid-May within 5m of the centre
marker of each population. For each gall collected I began by measuring
horizontal diameter. I then scored each gall containing Eurostaas a survivor, those with large holes as having been killed by a bird,
and those containing other larvae as having been killed by the
corresponding enemy (e.g. Eurytoma gigantea ). I scored empty
galls with no sign of habitation as early larval death (Abrahamson et
al. 1989). Note that mortality is often high (Weis and Kapelinski 1994,
Start 2018b), suggesting that survival is a key fitness component.
Further note that gall size is unrelated to larval mass or size of the
adult fly (Hess et al. 1996), suggesting that gall size is unlikely to
be correlated with other components of fitness like fecundity or mating
success.
In addition to measuring individual gall size and species interactions,
I also collected key environmental information. I recorded the number of
stems out of 100 randomly selected goldenrod that were knocked down and
the distance of the population from trees. All three metrics have
previously been shown to influence bird attack, and in some cases
selection. Furthermore, I estimated density by counting the number of
galls on 100 randomly selected goldenrod stems—density should increase
following years with high survival but decline following years when
enemy attack was high.
In late June 2019, I measured the density (galls per goldenrod stem) of
galls in each patch, and measured the horizontal diameter of up to 20
galls per population. Note that these measurements were taken on the
2019/2020 generation, and were taken to measure the ecological
(demographic) and evolutionary (trait change) consequences of the
previous year’s extreme event (i.e. that occurred in the 2018/19
generation). Together these data represent demographic information
(survival and density), species interactions (attack rates), and the
fodder to measure natural selection and evolutionary change (trait
values).