Figure 1. Chart describing processes and predictions of the hypotheses. Panel (a) describes the underlying processes that may give rise to the patterns predicted by the outlined hypotheses. Underpinning hypothesis 1 (either phenology or range shift) is the assumption that species differ fundamentally in their abilities to adjust either in situ or via dispersal. As both strategies are likely to be adaptive, being able to use either will lead to an increased probability of presence, which should be reflected in positive population trends. Positive feedback loops through larger population size further enhance the ability of both mechanisms to act. Underpinning hypothesis 2 (both phenology and range shift), on the other hand, is the assumption that adaptive in situ responses in phenology increases the fitness of the individuals, leading to higher rates of survival and/or more offspring. This in turn increases the probability of presence (stronger population trends) and thus higher colonization rates which leads to the species being able to expand into habitats becoming suitable as climate changes (=shift in the northern range boundary (NRB)). In this study, the hypothesized underlying processes are investigated through proxies for range shift, phenology shift, and probability of presences as depicted by derived estimates in yellow versus blue font in the process charts: shift in NRB as a measure of species range shift; change in adult flight period as a proxy for phenology shift; and population trends as a proxy for probability of presence across the distribution. Panel (b) describes the expected patterns in the data, i.e. the combinations of responses, as regards NRB and phenology shift estimates, that would support hypotheses 1 (either advanced phenology or northwards shifting NRB), 2 (both advanced phenology and northwards shifting NRB), and 0 (neither advanced phenology nor northwards shifting NRB). Although these proxies do not allow us to infer evidence for the underlying processes, they can inform us of the patterns across a wide sample of species. By combining them with information on population trends, we can infer how successful the strategies are on their own and in combination for species experiencing climate change, and what may be the consequences if species cannot utilize either of the highlighted strategies.