Research

Completed Projects:

Should models used to examine impacts of population change incorporate density-dependence mechanisms? A case study based on seabirds and wind fadownloadrm

Although density-dependent regulation of population growth is thought to be relatively widespread in nature, density-independent models are often used to project the population response to drivers of change. The risk of this approach is that studies can fail to provide robust and defensible estimates of effect sizes and overlook mechanisms that could result in extinction. Currently there is debate about including density-dependent mechanisms in models that assess the effect of offshore wind farms on marine bird populations. Density-dependence is considered to be poorly understood for this group, and therefore it is either excluded from these models or incorporated in a form that has little empirical validation. We reviewed the evidence for compensatory (i.e. negative density dependence) and depensatory (i.e. positive density dependence) regulation of 31 marine bird species. The evidence was evaluated in relation to established indices of wind farm vulnerability and a meta-analysis was conducted to examine the functional shape of density-dependent population growth.

Collaborators: Dr. Rob Robinson (British Trust for Ornithology); Dr. Sue O’Brien (Joint Nature Conservation Committee).

Funded by: British Trust for Ornithology and Joint Nature Conservation Committee

 

The relative roles of top-down and bottom-up forces driving population change in macaroni penguins

Macaroni penguins at SouthIMG_8336 Georgia declined by c. 70% between 1985 and 2012. The aim of this study was to combine demographic, environmental and population dynamics data in order to examine the drivers of population change. I used mark–recapture modelling to examine how survival rates were influenced by individual traits, environmental change and predation pressure, and combined these findings with time series of population counts and productivity in a state-space population model. By subjecting this model to a sensitivity analysis it was possible to examine the links between individual covariates, demographic rates, and the overall population trajectory.

Collaborators: Prof Jason Matthiopoulos (Univeristy of Glasgow), Dr. Norman Ratcliffe (British Antarctic Survey), Dr. Jonathan Green (University of Liverpool), Dr Jaume Forcada (British Antarctic Survey), Dr Richard Phillips (British Antarctic Survey).

Funded by: Natural Environment Research Council

 

Drivers of intrapopulation variation in resource use in a generalist predator, the macaroni penguin

mapIntrapopulation variation in resource use occurs in many populations of generalist predators with important community and evolutionary implications. One of the hypothesised mechanisms for such widespread variation is ecological opportunity, i.e. resource availability determined by intrinsic constraints and extrinsic conditions. In this study, we combined tracking data and stable isotope analysis to examine how breeding constraints and prey conditions influenced intrapopulation variation in resource use in a generalist predator, the macaroni penguin. Isotopic variation was also examined as a function of breeding success, individual traits and individual specialisation. This study highlights the importance of considering ecological interactions that operate on multiple spatio-temporal scales when examining the drivers of resource use in populations of generalist predators.

Collaborators: Prof Jason Matthiopoulos (Univeristy of Glasgow), Dr. Norman Ratcliffe (British Antarctic Survey), Dr. Jonathan Green (University of Liverpool), Dr. Tamsin O’Connell (University of Cambridge).

Funded by: Natural Environment Research Council

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