Ecological complexity and the biosphere: the next 30 years

Abstract

Global warming, habitat loss and overexploitation of limited resources are leading to alarming biodiversity declines. Ecosystems are complex adaptive systems that display multiple alternative states and can shift from one to another in abrupt ways. Some of these tipping points have been identified and predicted by mathematical and computational models. Moreover, multiple scales are involved and potential mitigation or intervention scenarios are tied to particular levels of complexity, from cells to human-environment coupled systems. In dealing with a biosphere where humans are part of a complex, endangered ecological network, novel theoretical and engineering approaches need to be considered. At the centre of most research efforts is biodiversity, which is essential to maintain community resilience and ecosystem services. What can be done to mitigate, counterbalance or prevent tipping points? Using a 30-year window, we explore recent approaches to sense, preserve and restore ecosystem resilience as well as a number of proposed interventions (from afforestation to bioengineering) directed to mitigate or reverse ecosystem collapse. The year 2050 is taken as a representative future horizon that combines a time scale where deep ecological changes will occur and proposed solutions might be effective. This article is part of the theme issue 'Ecological complexity and the biosphere: the next 30 years'.

Keywords: biodiversity; bioengineering; climate change; ecological networks; restoration; tipping points.

Figure 1.

Ecological complexity challenges for 2050. With the rise of global temperatures, population growth and the resulting pressure on resources and habitats, biodiversity will face major threats. One crucial role of science is to develop reliable predictions of future trends. Here, four examples are chosen (left) along with current forecasts (central column, estimated 2050 states indicated with a red circle) and examples of the complex systems approaches used (right). (a) Urban centres (image of Central Park, New York, by Ajay Suresh, Creative Commons) are rapidly expanding as massive migrations occur towards cities. Human population growth (centre) is slowly decelerating, but two extra billion humans will be added to the current numbers, reaching 9.7 billion by 2050. The current trend is a consequence of the nonlinearities associated with hyperbolic dynamics, which predicts a singularity at a given finite time t_c (right). (b) Rainforests (left image by Gleilson Miranda, Creative Commons) are experiencing rapid loss and fragmentation of their habitats, with predicted critical points (centre plot, grey bar, see [2]) to be reached in a few decades. These critical points correspond to percolation thresholds (right panel). (c) Drylands (image courtesy of David Huber) are expanding and will grow from the current 40% to more than 50% in just three decades. Models of drylands involving vegetation cover as a key variable predict sharp transitions between alternative states, connected through three different shifts [3]. Here two of them are indicated. (d) Marine ecosystems, and coral reefs (left image by Toby Hudson, Creative Commmons) in particular, are being affected by warming ocean temperatures, eutrophication, pathogens and overfishing. Reef cover is rapidly shrinking and might experience massive decays in the next decades. Here, the previous and predicted time series of coral reef cover in Hawaii is shown (centre, data from https://19january2017snapshot.epa.gov/cira/climate-action-benefits-coral-reefs_.html). Multiple alternative states have been identified (right) with different sources of stress causing jumps from one state to another.

Figure 2.

Scales, models and interventions. Our understanding of different patterns and processes in ecosystems, from molecules and cells to the global climate can be explored by a diverse range of mathematical models (central column). Each model addresses a given scale and is intended to answer specific questions that make sense on that scale. Here, we have used drylands as a case study. Four potential levels of study are: (a) large-scale dynamics taking place on the regional/continental level, where the social component might be needed; these models, along with remote sensing data and other sources of information, can help to define a global resilience index; (b) spatio-temporal processes associated with community dynamics involving facilitation; (c) species-level models introducing both low-dimensional pairwise exchanges and phenology; and (d) soil microbiome dynamics, where models can consider diverse levels of description (including multispecies equations). In the right column, four examples of interventions are indicated: (e) large-scale reforestation or afforestation, with the African Green Wall as one particularly relevant case study (image by UNCCD) aimed at creating a 7000 km long barrier; (f) implementing global policies to limit overfishing; (g) straw checkerboards used to allow planting of sand-binding vegetation in the Tengger desert leading to soil restoration (image from [86]); (h) green seawalls close to urban coastal areas.) Species-specific interventions can be designed for keystone species (KS). This is the case for Joshua trees (i) in drylands or kelp forests (j) in marine coastal communities. (k) Both restoration and bioengineering strategies can be developed by using cyanobacteria as key components of soil communities used to improve structural cohesion, enhance organic carbon and/or water storage. (l) Similar goals can be achieved by using synthetic microbiomes to increase resilience of corals.