by Anja Marie Westram
Prey animals protect themselves from predators by using camouflage colors. Fish can move quickly in the water due to their elongated shape. Plants use scents to attract pollinating insects: adaptations of living beings to their environment are omnipresent. Such adaptations are determined in the organism's genes and arise through evolutionary processes over generations - unlike many behaviors, for example, they are not spontaneously influenced by the environment over the course of life. A rapidly changing environment therefore leads to “maladaptation”. Physiology, color or body structure are then no longer adapted to the environment, so that reproduction and survival are more difficult, the population size decreases and the population may even die out.
The man-made increase in greenhouse gases in the atmosphere is changing the environment in many ways. Does this mean that many populations are no longer well adapted and will become extinct? Or can living beings also adapt to these changes? So, over the course of a few generations, will animals, plants and fungi emerge that are better able to cope with, for example, heat, drought, ocean acidification or reduced ice cover of bodies of water and can therefore survive climate change well?
Species follow the climate to which they are already adapted and become locally extinct
In fact, laboratory experiments have shown that populations of some species can adapt to changing conditions: in an experiment at the Vetmeduni Vienna, for example, fruit flies laid significantly more eggs after just over 100 generations (not a long time, as fruit flies reproduce quickly) under warm temperatures and had changed their metabolism (Barghi et al., 2019). In another experiment, mussels were able to adapt to more acidic water (Bitter et al., 2019). And what does it look like in nature? There, too, some populations show evidence of adaptation to changing climatic conditions. The report of Working Group II of the IPCC (Intergovernmental Panel on Climate Change) summarizes these results and emphasizes that these patterns were found primarily in insects, which, for example, start their “winter break” later as an adaptation to longer summers (Pörtner et al ., 2022).
Unfortunately, scientific studies increasingly suggest that (sufficient) evolutionary adaptation to the climate crisis is likely to be the exception rather than the rule. The distribution areas of numerous species are shifting to higher altitudes or towards the poles, as also summarized in the IPCC report (Pörtner et al., 2022). The species therefore “follow” the climate to which they are already adapted. Local populations at the warmer edge of the range often do not adapt but migrate or die out. A study shows, for example, that 47% of the 976 animal and plant species analyzed have (recently) extinct populations at the warmer edge of the range (Wiens, 2016). Species for which a sufficient shift in the distribution area is not possible - for example because their distribution is limited to individual lakes or islands - can also die out completely. One of the first species proven to have become extinct due to the climate crisis is the Bramble Cay mosaic-tailed rat: it was only found on a small island in the Great Barrier Reef and was unable to avoid repeated floods and climate-related vegetation changes (Waller et al., 2017).
For most species, sufficient adaptation is unlikely
How many species will be able to adapt sufficiently to increasing global warming and ocean acidification and how many will become extinct (locally) cannot be predicted precisely. On the one hand, the climate forecasts themselves are subject to uncertainty and often cannot be made on a sufficiently small scale. On the other hand, in order to make a prediction for a population or species, one would have to measure its genetic diversity relevant to climate adaptation - and this is difficult even with expensive DNA sequencing or complex experiments. However, we know from evolutionary biology that sufficient adaptation is unlikely for many populations:
- Rapid adaptation requires genetic diversity. With regard to the climate crisis, genetic diversity means that individuals in the original population, for example, cope differently with high temperatures due to genetic differences. Only if this diversity is present can warm-adapted individuals increase in the population during warming. Genetic diversity depends on many factors – for example the size of the population. Species whose natural range includes climatically different habitats have an advantage: genetic variants from already warm-adapted populations can be “transported” to warmer areas and help cold-adapted populations survive. On the other hand, when climate changes lead to conditions to which no population of the species is yet adapted, there is often not enough useful genetic diversity - this is exactly what happens in the climate crisis, especially at the warmer edges of distribution areas (Pörtner et al., 2022).
- Environmental adaptation is complex. Climate change itself often imposes multiple requirements (changes in temperature, precipitation, storm frequency, ice cover…). There are also indirect effects: the climate also affects other species in the ecosystem, for example on the availability of forage plants or the number of predators. For example, many tree species are not only exposed to greater drought, but also to more bark beetles, as the latter benefit from warmth and produce more generations per year. Trees that are already weakened are put under additional strain. In Austria, for example, this affects spruce (Netherer et al., 2019). The more different challenges the climate crisis presents, the less likely successful adaptation becomes.
- The climate is changing too quickly due to human influences. Many adaptations that we observe in nature have arisen over thousands or millions of generations - the climate, on the other hand, is currently changing drastically within just a few decades. In species that have a short generation time (i.e. reproduce quickly), evolution occurs relatively quickly. This could partly explain why adaptations to anthropogenic climate change have often been found in insects. In contrast, large, slow-growing species, such as trees, often take many years to reproduce. This makes it very difficult to keep up with climate change.
- Adaptation does not mean survival. Populations may well have adapted to climate changes to a certain extent - for example, they can survive heat waves better today than before the industrial revolution - without these adaptations being sufficient to survive warming of 1,5, 2 or 3°C in the long term. In addition, it is important that evolutionary adaptation always means that poorly adapted individuals have few offspring or die without offspring. If this affects too many individuals, the survivors may be better adapted - but the population may still shrink so much that it dies out sooner or later.
- Some environmental changes do not allow for quick adjustments. When a habitat changes fundamentally, adaptation is simply inconceivable. Fish populations cannot adapt to life in a dry lake, and land animals cannot survive if their habitat is flooded.
- The climate crisis is just one of several threats. Adaptation becomes more difficult the smaller the populations, the more fragmented the habitat, and the more environmental changes occur at the same time (see above). Humans are making adaptation processes even more difficult through hunting, habitat destruction and environmental pollution.
What can be done about extinction?
What can be done when there is no hope that most species will adapt successfully? The extinction of local populations will hardly be preventable - but at least various measures can counteract the loss of entire species and the shrinking of distribution areas (Pörtner et al., 2022). Protected areas are important to preserve species where they are well adapted and to preserve existing genetic diversity. It is also important to connect the different populations of a species so that warm-adapted genetic variants can spread easily. For this purpose, natural “corridors” are being established that connect suitable habitats. This can be a hedge that connects different stands of trees or protected areas in an agricultural area. The method of actively transporting individuals from threatened populations to areas (e.g. at higher altitudes or higher latitudes) where they are better adapted is somewhat more controversial.
However, the consequences of all these measures cannot be precisely estimated. Although they can help maintain individual populations and entire species, each species responds differently to climate change. Ranges shift in different ways and species meet in new combinations. Interactions such as food chains can change fundamentally and unpredictably. The best way to preserve biodiversity and its invaluable benefits for humanity in the face of the climate crisis is still to effectively and quickly combat the climate crisis itself.
Barghi, N., Tobler, R., Nolte, V., Jakšić, AM, Mallard, F., Otte, KA, Dolezal, M., Taus, T., Kofler, R., & Schlötterer, C. (2019 ). Genetic redundancy fuels polygenic adaptation in Drosophila. PLOS Biology, 17(2), e3000128. https://doi.org/10.1371/journal.pbio.3000128
Bitter, MC, Kapsenberg, L., Gattuso, J.-P., & Pfister, CA (2019). Standing genetic variation fuels rapid adaptation to ocean acidification. Nature Communications., 10(1), Article 1. https://doi.org/10.1038/s41467-019-13767-1
Netherer, S., Panassiti, B., Pennerstorfer, J., & Matthews, B. (2019). Acute drought is an important driver of bark beetle infestation in Austrian Norway spruce stands. Frontiers in Forests and Global Change, 2. https://www.frontiersin.org/articles/10.3389/ffgc.2019.00039
Pörtner, H.-O., Roberts, DC, Tignor, MMB, Poloczanska, ES, Mintenbeck, K., Alegría, A., Craig, M., Langsdorf, S., Löschke, S., Möller, V., Okem, A., & Rama, B. (Eds.). (2022). Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.
Waller, NL, Gynther, IC, Freeman, AB, Lavery, TH, Leung, LK-P., Waller, NL, Gynther, IC, Freeman, AB, Lavery, TH, & Leung, LK-P. (2017). The Bramble Cay melomys Melomys rubicola (Rodentia: Muridae): A first mammalian extinction caused by human-induced climate change? wildlife research, 44(1), 9–21. https://doi.org/10.1071/WR16157
Wiens, J.J. (2016). Climate-related local extinctions are already widespread among plant and animal species. PLOS Biology, 14(12), e2001104. https://doi.org/10.1371/journal.pbio.2001104
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