11 Mass Extinction
Bendell
The last mass extinction of life on earth, where 95% of species disappeared, was due to methane-induced rapid warming of the atmosphere (Lee, 2014; Brand et al, 2016).
Bendell (2018) Deep Adaption: A Map for Navigating Climate Tradegy (pdf)
11.1 Plants and Fungi
Carbonbrief
The “State of the World’s Plants and Fungi” report, which is based on both peer-reviewed and preliminary studies, also says that almost half of all flowering plant species could be at risk of extinction.
Habitat and land-use changes are the biggest threat to plants and fungi, but climate change is expected to become an even larger issue in the future
Five key findings:
- Three in four unknown plant species are at risk of extinction
- Climate change is having ‘detrimental’ impacts on fungi
- Plants are currently going extinct 500 times faster than before humans existed
- Scientists have assessed the risk of extinction for less than 1% of known fungi species
- Almost half of flowering plant species are under threat
The new research by Kew scientists analysed data from the World Checklist of Vascular Plants and the International Union for Conservation of Nature (IUCN) red list of threatened species – a global assessment of the extinction risk status of different animals, plants and fungi.
The researchers examined the links between the year a plant species was formally described and its extinction risk. The findings, outlined in the chart below, show that the later a species is formally identified and described by science, the higher chance it has of being deemed at risk.
Fig: The observed proportion (red bars) and predicted probability (yellow line) of threatened species by the year in which they were described.
Based on this finding, Kew scientists are calling for all newly described plant species to be “presumed threatened with extinction unless proven otherwise”.
The IUCN extinction criteria used does not give a timeframe estimate for when an extinction is likely to occur.
Unless formal naming accelerates we are in danger of losing species before they have been described.
The main threat to both plant and fungi species is habitat loss and land-use change in the form of forestry, agriculture or residential and commercial development. Climate change is having “detrimental” impacts on fungi in different ways with changes in temperature and moisture levels having a direct impact.
Plants are currently going extinct 500 times faster than before humans existed.
Carbonbrief (2023) Kew report: Five key extinction risks facing the world’s plants and fungi
11.2 Insects
Klink Abstract
Studies have reported widespread declines in terrestrial insect abundances in recent years but trends in other biodiversity metrics are less clear-cut. Here we examined long-term trends in 923 terrestrial insect assemblages monitored in 106 studies, and found concomitant declines in abundance and species richness. For studies that were resolved to species level (551 sites in 57 studies), we observed a decline in the number of initially abundant species through time, but not in the number of very rare species. At the population level, we found that species that were most abundant at the start of the time series showed the strongest average declines (corrected for regression-to-the-mean effects). Rarer species were, on average, also declining, but these were offset by increases of other species. Our results suggest that the observed decreases in total insect abundance can mostly be explained by widespread declines of formerly abundant species. This counters the common narrative that biodiversity loss is mostly characterized by declines of rare species. Although our results suggest that fundamental changes are occurring in insect assemblages, it is important to recognize that they represent only trends from those locations for which sufficient long-term data are available. Nevertheless, given the importance of abundant species in ecosystems, their general declines are likely to have broad repercussions for food webs and ecosystem functioning.
Klink Memo
Often confused, however, is exactly which measures of insect biodiversity are being considered. Biodiversity is not a single metric, but rather a generalized concept that encompasses the numbers of individuals and species, species’ relative abundances (for example, evenness and numbers of rare and common species), as well as the identities of species and their interactions. All of these aspects of biodiversity inform the changes that are occurring to insect biodiversity, and might reveal hitherto-overlooked—but crucial—changes. However, although declines in insect abundance and biomass have been shown in large-scale studies and syntheses, trends in other biodiversity metrics have been less clear. Species richness, for example, has been found to decline along with abundance in some large studies, whereas in other studies, insect richness was reported to be stable
A better understanding of declines in insect abundance can emerge through the study of multiple (complementary) measures of biodiversity, and, in particular, by examining trends in rare and abundant species. For example, even if overall abundances of terrestrial insects are declining, there are several possible scenarios by which other metrics of biodiversity can concurrently change depending on how species with different relative abundances respond.
Klink (2023) Disproportionate declines of formerly abundant species underlie insect loss
11.3 Coral Reefs
Bad news from the Coral Reefs. Bleaching is going on and reefs are not healing between events UNEP is reporting on this issue.
From the 2020 report:
Stony corals bleach when warm sea temperatures disrupt the mutualistic relationship between the algal symbionts, called zooxanthellae, that reside within the host coral tissues (Douglas 2003). Corals can either regain their zooxanthellae (Baker 2001) and survive or die if temperature stress persists. The third global coral bleaching event, which started in 2014 and extended well into 2017, was the longest coral bleaching event on record (Eakin et al. 2019). The length of the event means corals in some parts of the world had no time to recover in 2014, 2015 or 2016 during the cool/winter season, prior to experiencing bleaching the following year. Van Hooidonk et al. (2013, 2014, 2016 and 2017) found that a majority of coral reefs are projected to experience annual severe bleaching (ASB) by the mid-2040’s under a business-as- usual emissions scenario (RCP8.5). This means that the recent global bleaching event of 2014- 2017 represents what climate models suggest may become the norm over the coming few decades. Lower frequencies of bleaching events per decade (e.g., 2x or 4x per decade) are projected to occur earlier than ASB. ASB is projected here because annual severe bleaching is a time beyond which coral reefs seem certain to change (and possibly rapidly degrade). Importantly though, great spatial variation exists in the projected timing of the onset of ASB conditions among the world’s coral reefs. This variation will be a major driver of differences in the relative vulnerability of coral reef ecosystems to climate change.
In the IPCC’s widely adopted vulnerability assessment framework, vulnerability is a function of exposure to climate and non-climate threats and sensitivity to these threats, which yields potential impacts that are moderated by adaptive capacity (Turner et al. 2003). Sensitivity and adaptive capacity can be collectively seen as resilience (Marshall and Marshall 2007), i.e., the capacity of a system to absorb or withstand stressors such that the system maintains its structure and functions in the face of disturbance and change, and the capacity to adapt to future challenges (McLeod et al. 2019). Managing coral reefs for resilience entails reducing coral reef vulnerability to climate change by reducing exposure to non-climate threats (i.e., local- scale anthropogenic stress, Anthony et al. 2014).
A key challenge for reef management lies in deciding where to target actions to reduce anthropogenic stress, ensuring efficacy as well as cost effectiveness of actions taken. Ecosystem and Resilience Based Management (EBM and RBM) are becoming increasingly sophisticated (Mills et al. 2015, McLeod et al. 2019), and software that combines and analyzes spatial data is increasingly accessible and used in planning to strike a balance between what can be competing conservation and development objectives (Watts et al. 2009). For example, protecting biodiversity, providing for sustainable fisheries, and minimizing user conflicts are among the highest priorities during marine spatial planning (MSP) efforts in reef areas (Agardy et al. 2011). Incorporating spatial variation in coral reef vulnerability to climate change is frequently discussed during MSP but, as yet, is rarely operationalized (Anthony et al. 2014). This will require assessing spatial variation in the key vulnerability components – exposure and resilience - at a locally relevant scale (one km to 10s of km).
UNEP Coral Bleaching Futures 2017 (pdf)
11.4 Extinction Rate
11.4.1 Compared to 5th Mass Extinction
Neubauer Abstract
The Cretaceous–Paleogene mass extinction event 66 million years ago eradicated three quarters of marine and terrestrial species globally. However, previous studies based on vertebrates suggest that freshwater biota were much less affected. Here we assemble a time series of European freshwater gastropod species occurrences and inferred extinction rates covering the past 200 million years. We find that extinction rates increased by more than one order of magnitude during the Cretaceous–Paleogene mass extinction, which resulted in the extinction of 92.5% of all species. The extinction phase lasted 5.4 million years and was followed by a recovery period of 6.9 million years. However, present extinction rates in European freshwater gastropods are three orders of magnitude higher than even these revised estimates for the Cretaceous–Paleogene mass extinction. Our results indicate that, unless substantial conservation effort is directed to freshwater ecosystems, the present extinction crisis will have a severe impact to freshwater biota for millions of years to come.