There is evidence that human influence may be forcing the global ecosystem towards a rapid, irreversible, planetary-scale shift into a state unknown in human experience. Most forecasts of how the biosphere will change in response to human activity are rooted in projecting trajectories. Such models tend not anticipate critical transitions or tipping points, although recent work indicates a high probability of those taking place. And, at a local scale, ecosystems are known to shift abruptly between states when critical thresholds are passed. These authors review the evidence from across ecology and palaeontology that such a transition is being approached on the scale of the entire biosphere. They go on to suggest how biological forecasting might be improved to allow us to detect early warning signs of critical transitions on a global, as well as local, scale. Localized ecological systems are known to shift abruptly and irreversibly from one state to another when they are forced across critical thresholds. Here we review evidence that the global ecosystem as a whole can react in the same way and is approaching a planetary-scale critical transition as a result of human influence. The plausibility of a planetary-scale ‘tipping point’ highlights the need to improve biological forecasting by detecting early warning signs of critical transitions on global as well as local scales, and by detecting feedbacks that promote such transitions. It is also necessary to address root causes of how humans are forcing biological changes.

/pdf/approaching-a-state-shift-in-earth-s-biosphere-433h7hm56c.pdf

Approaching a state shift in Earth’s biosphere

Understanding the ecological impacts of climate change is a crucial challenge of the twenty-first century. There is a clear lack of general rules regarding the impacts of global warming on biota. Here, we present a metaanalysis of the effect of climate change on body size of ectothermic aquatic organisms (bacteria, phyto- and zooplankton, and fish) from the community to the individual level. Using long-term surveys, experimental data and published results, we show a significant increase in the proportion of small-sized species and young age classes and a decrease in size-at-age. These results are in accordance with the ecological rules dealing with the temperature–size relationships (i.e., Bergmann's rule, James' rule and Temperature–Size Rule). Our study provides evidence that reduced body size is the third universal ecological response to global warming in aquatic systems besides the shift of species ranges toward higher altitudes and latitudes and the seasonal shifts in life cycle events.

/pdf/global-warming-benefits-the-small-in-aquatic-ecosystems-g9kqvuk94x.pdf

Global warming benefits the small in aquatic ecosystems

1. What are Allee effects? 2. Mechanisms for Allee effects 3. Population dynamics: modelling demographic Allee effects 4. Genetics and evolution 5. Conservation and management 6. Conclusions and perspectives

Allee Effects in Ecology and Conservation

The effect of ecological change on evolution has long been a focus of scientific research. The reverse—how evolutionary dynamics affect ecological traits—has only recently captured our attention, however, with the realization that evolution can occur over ecological time scales. This newly highlighted causal direction and the implied feedback loop—eco-evolutionary dynamics—is invigorating both ecologists and evolutionists and blurring the distinction between them. Despite some recent relevant studies, the importance of the evolution-to-ecology pathway across systems is still unknown. Only an extensive research effort involving multiple experimental approaches—particularly long-term field experiments—over a variety of ecological communities will provide the answer.

https://science.sciencemag.org/content/sci/331/6016/426.full.pdf

The Newest Synthesis: Understanding the Interplay of Evolutionary and Ecological Dynamics

Numerous groundfish stocks in both the Atlantic and Pacific are considered overfished, resulting in large-scale fishery closures. Fishing, in addition to simply removing biomass, also truncates the age and size structure of fish populations and often results in localized depletions. We summarize recent research suggesting that an old-growth age structure, combined with a broad spatial distribution of spawning and recruitment, is at least as important as spawning biomass in maintaining long-term sustainable population levels. In particular, there is evidence that older, larger female rockfishes produce larvae that withstand starvation longer and grow faster than the offspring of younger fish, that stocks may actually consist of several reproductively isolated units, and that recruitment may come from only a small and different fraction of the spawning population each year. None of these phenomena is accounted for in current management programs. We examine alternative management measures that addre...

Fisheries Sustainability via Protection of Age Structure and Spatial Distribution of Fish Populations

Northern cod, comprising populations of Atlantic cod (Gadus morhua) off southern Labrador and eastern Newfoundland, supported major fisheries for hundreds of years. But in the late 1980s and early 1990s, northern cod underwent one of the worst collapses in the history of fisheries. The Canadian government closed the directed fishing for northern cod in July 1992, but even after a decade-long offshore moratorium, population sizes remain historically low. Here we show that, up until the moratorium, the life history of northern cod continually shifted towards maturation at earlier ages and smaller sizes. Because confounding effects of mortality changes and growth-mediated phenotypic plasticity are accounted for in our analyses, this finding strongly suggests fisheries-induced evolution of maturation patterns in the direction predicted by theory. We propose that fisheries managers could use the method described here as a tool to provide warning signals about changes in life history before more overt evidence of population decline becomes manifest.

https://www.iiasa.ac.at/~dieckman/reprints/OlsenEtal2004.pdf

Maturation trends indicative of rapid evolution preceded the collapse of northern cod

Otolith elemental fingerprints as biological tracers of fish stocks

By estimating probabilistic reaction norms for age and size at maturation, we show that maturation schedules of Atlantic cod (Gadus morhua) off Labrador and Newfoundland shifted toward earlier ages...

/pdf/assessing-changes-in-age-and-size-at-maturation-in-2ak67wut1e.pdf

Assessing changes in age and size at maturation in collapsing populations of Atlantic cod (Gadus morhua)

We examined variation at seven microsatellite loci (Gmo3, Gmo8, Gmo19, Gmo34, Gmo35, Gmo36, and Gmo37) and PanI in some 5230 Atlantic cod (Gadus morhua) from 19 inshore and offshore locations around Newfoundland and Labrador. The mean F ST estimate over all loci was 0.0080. Overall, the cod populations surveyed conformed to an isolation-by-distance structure, cod from more distant locations tending to be more genetically distinct. Among offshore sites, the Flemish Cap population (NAFO Division 3M) was the most distinctive, and among inshore sites, the Gilbert Bay population in southern Labrador (2J) was the most distinctive. In NAFO Divisions 3KL, no significant genetic differentiation was observed among inshore northern cod sampled in four bays (Notre Dame, Bonavista, Trinity, and Conception) along the northeast coast of Newfoundland, and the data do not support the hypothesis of separate “bay stocks”. Annual variation within sampling sites was as large, on average, as the differentiation among sampling sites. The inshore northern cod were distinct from the population in Gilbert Bay and from most offshore northern cod populations. On average, over all populations, regional differences in allele frequencies were seven times larger than annual variation. The offshore samples were more heterogeneous, and there may be at least three distinct offshore spawning populations of northern cod. In Subdivision 3Ps, no consistent differentiation was observed among sampling sites, two in inshore bays (Placentia, Fortune), and two offshore (Burgeo Bank, Halibut Channel). The southern Grand Bank (Divisions 3NO) may have a separate spawning population from those in other offshore sites, but additional sampling is required to confirm population distinctiveness.

/pdf/multiple-stock-structure-of-atlantic-cod-gadus-morhua-off-397uljovle.pdf

Multiple stock structure of Atlantic cod (Gadus morhua) off Newfoundland and Labrador determined from genetic variation

Stomachs of 270 phocids from five species (bearded, Erignathus barbatus; hooded, Cystophora cristata; grey, Halichoerus grypus; harbour, Phoca vitulina; and ringed, P. hispida), collected off Newfo...

John Brattey

Papers

Maturation trends indicative of rapid evolution preceded the collapse of northern cod

Otolith elemental fingerprints as biological tracers of fish stocks

Assessing changes in age and size at maturation in collapsing populations of Atlantic cod (Gadus morhua)

Multiple stock structure of Atlantic cod (Gadus morhua) off Newfoundland and Labrador determined from genetic variation

Host specificity and abundance of parasitic nematodes (Ascaridoidea) from the stomachs of five phocid species from Newfoundland and Labrador