On Ecological Mismatch
As a vast body of work exemplifies, summarised wonderfully in Sultan’s ‘Organism and Environment’, organisms cannot be separated from the environment in which they live. Environment changes organism, and organism changes environment, ad infinitum. Anthropogenic climate change is rapidly changing environments everywhere. Plastic and adaptive responses to phenology and distribution are weapons in the organism’s arsenal available in response to climate change. But are they sufficient to keep up? What are the community-wide effects of ecological shifts? And how do we incorporate answers to these questions into current and future conservation methods? We face considerable knowledge gaps in this field. Sometimes this encompasses ignorance of whole habitats; as Renner and Zohner (2018) note, we have “no long-term empirical data on the synchrony of trophic interactions in the tropics”. What research is needed to fill these gaps?
Below I outline thoughts and research ideas in aid of illuminating the above.
1. Secondary ecological mismatch;
Mismatch load
Organisms depend on other organisms in complex networks of interaction. We can simplify these webs by considering individual pairs or triplets of actors, which I term ‘ecological functional groups’ (EFGs) - for example, angiosperm – pollinator – predator. Environmental signals are changing (e.g. advancing thaw dates, increased precipitation, increased mean and absolute temperature). Consequently, the organisms of the EFG are at risk of mismatched with their environment. The existence of such mismatch is now well documented; I term this ‘primary ecological mismatch’, or mismatch with environment. Primary ecological mismatch generates responses (plastic or adaptive) from the organism to sustain fitness. The response, however, theoretically generates ‘secondary ecological mismatch’, or mismatch with ecological interactions. All members of the EFG respond to changing environmental cues, yet it is also understood that different taxa shift to alleviate mismatch to different extents (e.g. Saino et al., 2011; Ovaskainen et al., 2013). This creates pressure on organisms additional to that initially imposed by a changing environment – I term this ‘mismatch load’: the shift in environment and the ecology of other EFG members are separate phenomena. At a time where ecosystems face intense and extensive pressures, understanding and quantifying the mismatch load placed on EFGs by primary and secondary ecological mismatch is paramount.
How heritable are phenological strategies? How do plasticity and adaptation vary in their contributions to re-matching the environment?
Can higher order EFG members track changes in the basal member directly (for example, through intergenerational epigenetic mechanisms)? Is there a quantifiable impact of mismatch load on fitness? Which taxa are most risk of mismatch load, and how do we adjust conservation strategies to compensate for this?
A note on selective sweeps
To what extent is synchrony the result of active or passive processes? Active: phenotypic plasticity in trait. Passive: evolutionary process comprising selective sweep of less fit individuals. If passive, and occurring on small populations, how does ecological mismatch translate to extinction risk?
2. What happens at the limits of ecological realignment?
The timing of key environmental cues is changing; the distribution and phenology of organisms is changing as a result (both passively via localised extinctions and actively through plasticity and adaptation).
Take a theoretical scenario, where mean daily spring temperature is increasing. A signal used by plants for seedling sprouting, for example the date of first thaw, advances earlier into the year. In response, first sprouting advances too. Or in an alternative / additional example, we see distribution of this plant shift to higher altitudes where date of first thaw is unchanged. In both instances, there exists a theoretical limit where either: sprouting date cannot advance, or altitude cannot increase, without the plant experiencing a less optimal temperature.
What are fitness costs at the limits of resynchronising with the environment? How likely are we to reach this scenario? And how do we manage it?
3. How does ecological mismatch vary by habitat type?
Different habitats are comprised of different biological and physical characteristics. It is therefore expected that habitats will vary in their patterns of ecological shift and mismatch.
Long-term field experiments offer an exceptional resource for estimating differences in phenological patterns between habitats in the UK. Such experiments include the Buxton Climate Change Impacts Lab (upland grassland) and Cors Fochno, part of Dyfi NNR, (raised bog) and Shotover Country Park (heathland, woodland, and grassland), sites which boast ecological data broad in coverage and far-reaching in time. Understanding how patterns in ecological shifts vary between habitats could be a key tool for designing conservation policy, and targeting particular areas and species. For example, if mismatch load is found to be greatest in lowland heaths, developing conservation tools such as facilitated range shifts can be employed to level the playing field and conserve species at considerable risk of extinction.
When considering conservation priorities, Myers (2000) coined the idea of ‘biodiversity hotspots’. Tropical climates are a theme across many of these hotspots. In other words, we have a lot to lose from changes in the tropics. Put another way, if we don’t understand the changes happening in the tropics, we are set to lose. As mentioned, Renner and Zohner (2018) highlight the sparseness of data on phenological patterns in the tropics. Understanding the ecological shifts and associated mismatches occurring in this biome, at all levels from species to communities, is necessary for a full understanding of how climate change is impacting this habitat.
References
Myers, N., Mittermeier, R. A., Mittermeier, C. G., da Fonseca, G. A. B., Kent, J. (2000) Biodiversity hotspots for conservation priorities. Nature, 403, 853-858.
Ovaskainen, O., Skorokhodova, S., Yakovleva, M., Sukhov, A., Kutenkov, A., Kutenkova, N., Scherbakov, A., Meyke, E., del Mar Delgado, M. (2013) Community-level phenological response to climate change. PNAS, 110, 13434-13439.
Renner, S. S. & Zohner, C. M. (2018) Climate change and phenological mismatch in trophic interactions among plants, insects, and vertebrates. Annual Review of Ecology, Evolution, and Sytematics, 49, 165-182.
Saino, N., Ambrosini, R., Rubolini, D., von Hardenberg, J., Provenzale, A., Hüppop, O., Lehikoinen, A., Lehikoinen, E., Rainio, K., Romano, M., Sokolov, L. (2011) Climate warming, ecological mismatch at arrival and population decline in migratory birds. Proceedings Biological Sciences, 278, 835-842.