The coherence of ecological stability among ecosystems and across ecological scales

Lead Research Organisation: University of Sheffield
Department Name: School of Biosciences


Climate and environmental change is impacting on all ecosystems - marine, freshwater and terrestrial - in the world. The changes are associated with a wide range of 'stress' like rising temperature, drought, nutrient run-off, pesticides, over-harvesting and habitat loss. For example, more than 50% of freshwater aquatic communities that provide drinking water, recreation and food are threatened by detrimental anthropogenic stress in the last century, including rising temperature, pollution and N/P run-off. In marine communities, climate change, acidification, overfishing and pollution threaten food resources, coastal communities and carbon storage capacity. In terrestrial communities, rising temperatures, agricultural run-off, habitat fragmentation, pollution and more frequent extreme events threaten to forest, grassland and agricultural communities and the services they provide.

This detail suggests that the stability of populations, communities and ecosystem function is threatened by multiple, simultaneous stressors. Making predictions about these effects is hard. We highlight three substantial challenges to advancing the understanding of stability within and among ecosystems.

First, there are lots of ways to measure stability and dynamics and they work at different ecological scales - some are about individual species and others are about diversity of many species.. We must demonstrate the value of using simultaneously multiple measures and the appropriateness of them at different ecological scales.

Second, the kind of data we use to assess the stability and dynamics of organisms - numbers in time and space and among species - have properties that must be accounted for, but rarely are. We know that the numbers of a species today and yesterday are more related than numbers today and 5 years ago. This is temporal correlation. We know that populations that live close to each other will be more alike than those far apart. This is spatial correlation. And we know that species that are closely related will be more similar than distantly related ones. This is evolutionary correlation. The majority of stability indicators have failed to accommodate these disruptive and well know features of real data.

Third, there might be interactions among stressors. This means that the effect of one stressor depends on what the presence, absence or magnitude of another. This make prediction challenging, especially if we don't know about the dependencies. We need theory and data to understand how, and at what scales, multiple stressors impact stability.

Our project aims to deal with all of these using three research objectives.

1. Develop improved indicators of stability, at multiple ecological scales (e.g. biomass/abundance, community structure/diversity, function), that formally rectify long recognised but rarely addressed issues arising from spatial, temporal and phylogenetic covariation;
2. Make predictions about stability among ecosystems (coherence) facing multiple, simultaneous stressors produced by advanced simulation models that allow insight into the intrinsic processes and feedback mechanisms driving stability; and
3. Test model predictions and the efficacy of improved indicators of stability using experimental and field collected data from terrestrial, marine and freshwater ecosystems.

Planned Impact

The research proposed here is fundamental. It does however involve the analysis of large scale datasets linked to NERC/Defra research programmes on marine fisheries, CEH/UK Government data on freshwater and pan-european avian datasets overseen by the RSPB. Our work will establish a platform that informs on the common and distinct features of communities and drivers of environmental change that impact on the stability of ecological communities. Our set of tools and the cross-system analysis of stability will ultimately help scientists and natural resource managers understand if, how and when we can generalise about stability. In this context, we see three major groups of beneficiaries:

1. Policymakers and managers concerned with the conservation of biological diversity (marine, freshwater and terrestrial) in the face of environmental change. Our research will provide an understanding of the mechanisms that mediate response to environmental change, and how they facilitate stability at multiple scales.
2. The public, for whom food web networks provide an accessible route to understanding of complex ecological principles like stability and ecosystem function. Our focus on models and data that can be defined by networks lends itself to illustrating how well-known forms of environmental change can interact with biodiversity and ecosystem function and services. Our project provides an important opportunity for education and outreach, increasing public understanding of these key ecological principles.
3. 1st Year Minority/Women Students. In the past few years, there has been a decrease in the number of summer research bursaries available to young people interested in learning about science. Furthermore, the issues of supporting women and minorities in science (STEM) and computer programming has increased. Our research focused on STEM topics and computer modelling provides an ideal opportunity to experience a combination of ecology and conservation via computer based activities, to learn first -hand how research works and whether a career in research may be of interest.
Description Rewiring is the process by which connections in a food web are made and re-made during disturbances such as extinction and invasion. We have discovered that the frequency with which this is allowed to occur is important. The tradition has been to re-wire only after an 'event' like extinction or invasion happens. But re-wiring occurs all the time as a function of resource availability. This means that re-wiring can avert, delay or dampen the effects of extinctions or invasions.

We have discovered that the method for manipulating productivity/enrichment in the model community matters. We can generate changes with a 'global' term called carrying capacity that describes how much biomass of each species can be supported in an environment, or a more nuanced method where all species compete for 2 resources that determines their carrying capacity.

We have discovered that the mechanism by which links in a network rewire has a major impact on the outcome of extinctions. When one species goes extinct, others can too if the extinct species is a primary or only resource of another species. There are several proposed 'rules' for what happen to a species that loses its resources - it can look randomly for other species, for example, or for 'related' species of food, or can use optimal foraging theory. These options lead to rewiring either increasing (optimal foraging) or decreasing (random) robustness to secondary extinctions.

We have discovered how to allow temperature to impact communities via two mechanisms. The first relates to the fact that larger animals respond more slowly to temperature than smaller ones, because of their size and metabolism. This is the temperature-size rule. The second relates to thermal performance, where temperature impacts on the enzymatic and physiological processes of all living things, via the Bolzmann model. These two options generate different predictions about the impacts of temperature on community stability and structure.

We have discovered that the impacts of multiple stressors is dependent on how the ecological scale at which they act partitions their effects. In our experiments mixing temperature, productivity and harvesting levels, harvesting, which impacts directly on populations across multiple upper trophic levels, does not interact with the effect of the two other stressors which operate via physiology (temperature) or the basal trophic level only. This is a partitioning of multiple stressor effects predicted by our work about the importance of the targets and scales at which stressor act.

We have discovered that there is a major difference in model predictions about community structure, stability and diversity in computational experiments comparing the effects of two different temperatures vs. temperatures that gradually rise from the low to the high temperature. When the system is exposed to continuously increasing temperature species are buffered from temperature induced extinctions but the system it's self is much more unstable - both of these effects increase as the base line temperature increases.

We have discovered that trophic cascades, the positive indirect effect across non-adjacent trophic levels can extend across five trophic levels, evidenced from data analysis of North Sea fisheries, sea bird and mammal and phytoplankton data made possible by partnerships on the grant. This was Masters student work supervised by PDRAs on the project.

We have discovered that rewiring has an impact on the secondary extinction dynamics of complex food webs. Rewiring appears to increase robustness to secondary extinction, as predicted by many theories. This was Masters student work supervised by PDRAs on the project.
Exploitation Route This work combines modelling and data driven analyses from marine, terrestrial and freshwater ecosystems to generate understanding about the stability of ecosystems facing multiple simultaneous threats. Such theory, data driven analyses and predictions from the model will benefit those responsible for managing natural resources under the threats facing humanity around biodiversity loss, climate change and land use change.
Sectors Education,Environment

Description The PI and staff are beginning to share emerging results about the predictability and generality of multiple simultaneous threats to ecosystems, primarily through international seminars, conferences and applicant open day presentations. The climate crisis and associated environmental change is one of the most pressing challenges facing the world and ties closely to sustainable development goals that cut across science and public policy. We are developing a modelling platform to facilitate understanding how multiple simultaneous threats impact the biomass and diversity of species and the services supplied by ecological communities.
First Year Of Impact 2020
Sector Education,Environment
Description Multiple Open Day/Applicant Day Presentations - Networks in Biology 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact 30-120 students attended multiple open days/taster days over the past 2 years, sparking questions and discussions around network biology in social interactions, disease transmission, medicine and ecology.
Year(s) Of Engagement Activity 2020,2021