The timing of reproduction is important for fitness, and has been used to measure the
effect of widespread environmental change across ecosystems globally. Across
trophic levels, species occupying higher levels of a food web are generally adjusting
their timing of breeding in response to environmental change at a slower rate than
their prey (Poloczanska et al., 2013; Thackeray et al., 2010). This may lead to a
trophic mismatch between the energy requirements of consumers and the timing of
peak availability of resources during the crucial reproductive period, potentially
negatively impacting on fitness. However, the effects of environmental change have
not been uniform across populations, species, or regions of the world. This makes it
difficult to predict how different populations will adjust their response to environmental
change and the consequences of this for fitness. Marine species are generally
underrepresented in studies of environmental change, and seabirds are a group of
marine organisms that may be particularly at risk. They generally occupy higher
trophic levels, are long-lived, and reproduce slowly, meaning they may lack the
evolutionary capacity to adapt if the timing of key resources shifts rapidly under
climate change. However, the disconnected nature of previous studies of the trends
and drivers of seabird breeding phenology and the effects of trophic mismatch on
seabird fitness has precluded a global understanding of the extent to which seabirds
will respond to climate-mediated environmental change.
In this thesis, I make use of resources contributed by a global network of collaborators
to first establish the global average trends in seabird breeding phenology over time
and in response to sea surface temperature. I then identify which seabird populations
may be at higher risk of mismatch with prey by characterising sources of variance
around these phenological trends (e.g. due to differences in phylogeny, biogeographic
region, or life history traits). I go on to explore the scales at which phenology is
correlated across breeding North Atlantic seabird populations, to understand whether
it is likely that phenology is driven by conditions experienced by populations at the
breeding grounds, overwintering locations, or across multiple spatial scales. Finally, I
examine the fitness consequences of trophic mismatch between the resource and
consumer in two ways. I first use 30+ years of data from the long-term monitored
population of European shags Phalacrocorax aristotelis on the Isle of May, Scotland,
to identify the impact of trophic mismatch on population- and individual-level fitness
over time and in relation to changes in SST and diet. My final data chapter expands
the focus on the effects of mismatch on population level breeding success back to the
global scale. In the absence of detailed information on prey availability and phenology,
I develop on an existing framework that allows us to predict when phenological
change may impact on population level fitness to identify whether trophic mismatch is
both present in a population and getting worse over time. I use these criteria to
compare relationships across populations, regions and life history traits to identify the
prevalence of trophic mismatch across populations on a global scale
