The phenological optimum in space and time

For the many animals and plants that live in seasonal environments, getting the right timing to key life cycle events is vital. To take insectivorous woodland birds as an example, they must lay their eggs early in spring to ensure that their chicks will hatch and grow when food, such as caterpillars, is most plentiful. Because a full month elapses between starting to lay eggs and the maximum food demand of their chicks, the birds use cues in the environment in early spring, such as temperature, to predict what will happen later in the spring. An individual female can therefore be quite flexible in the timing of egg-laying, advancing the time by about two - five days (depending on the species) if spring temperatures are 1C warmer, an ability that we call plasticity. The prediction that the female makes about future conditions remains imperfect however; chicks will often be reared at the wrong time, resulting in few, if any, fledging. With rising spring temperatures the food peak may advance at a rate that is faster than individual birds can keep up with. Therefore, to keep up a species may need to evolve an earlier egg-laying date or, if this is not possible, it may ultimately go extinct.

Predicting how climate change will affect species has proven very difficult. If we know how much the optimum timing will shift for a 1C rise in temperature and we know how much a species can track this shift via plasticity, we can work out the amount of ground that evolution will need to make up. Measuring plasticity of timing in response to temperature, whether it be bird egg-laying, frog spawning, plant flowering or tree leafing, is relatively easy. Much more difficult is to work out the amount by which a species needs to shift its timing to track ideal conditions. In fact this has been done for just a single species, the great tit.

We will identify the relationship between spring temperatures and optimum timing for a second species, the blue tit, a close relative of the great tit. We will monitor blue tit egg-laying and the availability of caterpillars in four springs and across 50 sites that stretch north of Edinburgh for 200km. We will conduct a huge experiment, swapping hundreds of clutches between the nest boxes of incubating females, to establish when is the best time to lay. We think that the best laying date for a blue tit is likely to be governed by the relationship between temperature and the peak availability of caterpillars. However, the blue tit, like many species is a habitat and feeding generalist and it is possible that the relationship between spring temperature and the best time to lay will vary from one site to another as different caterpillar species become more or less abundant. We will test this idea and if we find support for it this implies that for generalist species we may need to identify the relationship between temperature and the optimum timing anew every time we consider a different population or habitat.

Clearly, we cannot expect this huge investment of time or resources to be expended on more than a handful of taxa and yet we need to know how temperature relates to the optimum timing for many taxa. We have developed a method that can infer this relationship from the type of observations on timings that citizen science projects like Nature's Calendar and the BTO Nest Record Scheme have been so effective at collecting. This could greatly increase the number of species for which we can identify this relationship. However, before we encourage much wider use of this method we need first to improve the statistical method and test whether the assumptions it requires are valid in the blue tit.

Below we identify the anticipated academic, societal and economic impacts of our research.

Academic Impacts

i. Enhancing knowledge economy: Our work will provide new insights into the effect of temperature on optimum timings and our ability to predict fitness consequences. Our results will be published in high impact journals and presented at national and international conferences. The spatially replicated data we collect will be of value to future projects focused on phenology and species interactions.

ii. Developing and training highly skilled researchers: One PDRA will be trained in high level Bayesian spatial statistics and the other (James Nicholls) will enhance his expertise in faecal metabarcoding. The project will train up to 19 RAs in the collection of standardised ecological data for a variety of taxa (trees, caterpillars, birds) and the value of spatial replication in project design.

iii. Developing and supporting new statistical methods: Co-I Hadfield has previously developed general-purpose software tools (such as MCMCglmm) that are widely used across many academic disciplines. We anticipate that the statistical advances we make in this project will be of value to evolutionary ecologists and to researchers from other fields with an interest in spatial processes.

Societal Impacts

i. Public Engagement and Education: The general public shows a great interest in phenology, particularly when it involves charismatic species, as evidenced by television programmes such as 'Springwatch' and 'Autumnwatch' and the media attention given to scientific publications on this topic. Furthermore, the popularity, breadth and longevity of citizen science phenology schemes in the UK (e.g., BTO Nest Record Scheme, Nature's Calendar, UK butterfly monitoring scheme) demonstrate that for a sizeable proportion of the general public this topic inspires exceptionally high-levels of engagement with the natural world. The public's engagement with birds is exceptional, as evidenced by the number of members boasted by the RSPB (> 1 million) and the number of participants in the RSPB Garden Birdwatch (519,000). Therefore, we are presented with a great opportunity to use the phenology of birds as a medium to educate the general public about the biotic impacts of climate change. In addition, for those who are already highly engaged with phenology (e.g., participants in citizen science phenology schemes), there is an opportunity to use this topic to educate in the design and implementation of ecological surveying. We anticipate that our work will be of a special interest to those living close to the transect.

ii. Policy (International, Government and Third Sector): The latest IPCC report identified the consequences of phenological mismatch as a key uncertainty in projecting the effects of climate change. We also have very limited evidence on which to infer whether species will respond to climate change via plasticity and/or evolution. Third sector conservation organisations (e.g., the RSPB, Woodland Trust), government advisors (e.g., Natural England, Scottish Natural Heritage, Natural Resources Wales, JNCC) and government agencies (e.g., Forestry Commission) have shown interest in addressing these knowledge gaps, as they are likely to have policy implications. To give one possible link between research outputs and policy - if we project that populations will be unable to keep up with the rate of climate change via plasticity alone then policy may advocate intensive interventions such as the promotion of habitat corridors to facilitate gene flow or, at the most extreme end, assisted migration.

Economic Impact

Invertebrate Surveying Tool: The faecal metabarcoding approach has potential applications as a tool for rapidly identifying and quantifying invertebrate biodiversity. There may be potential to develop this approach as a tool that can be used by environmental consultancies.