The evidence of climate change

The evidence of climate change

(Image: Barth Bailey)

Animals and plants are moving or dying: ‘phenological’ changes

Summary

  • The study of cyclic and seasonal natural phenomena, especially in relation to climate and plant and animal life, is called phenology (video 1).
  • Here in New Zealand, we’re familiar seasonal cycles: daffodils and migratory birds appearing in spring; the best times of year to plant seedlings and harvest food crops; falling leaves and shorter daylight hours signalling autumn.
  • While changes in daylight hours follow a predictable cycle because of Earth’s orbit around the sun, each year, winter doesn’t seem to last as long because temperatures are higher. Some plants are blossoming sooner, crops are ripening sooner, and fishermen are catching warmer water species they’ve never seen before. These and other changes in plants and animals are perhaps the most obvious attributes of climate change, and one we cannot deny: Earth’s climate is warming and species are on the move.

“Climate change has caused shifts in species’ distributions, changes in cyclic and seasonal behaviour, and altered population dynamics. In addition, it has caused further disruptions from the genetic to the ecosystem level in marine, terrestrial and freshwater ecosystems.”                   Department of Conservation

Phenological mismatches

Ecosystems are composed of plants and animalsincluding humansthat depend on one another for different life supporting ecosystem services through biological interactions. Phenological changes are the clearest evidence of climate change because there is no ambiguity; rising temperatures are having undeniable and costly consequences.

Example 1: A bird species lays eggs based on the number of daylight hours, so that its chicks hatch just as caterpillars are at their fattest (Fig. 1). But as the climate warms the caterpillar eggs hatch sooner. The birds can’t find food, the chicks starve, and meanwhile without predators the caterpillars gorge themselves on plants and produce a lot more eggs that hatch the following season, eating yet more plants (Fig. 2).

While some species might adapt by changing their diets, that in turn has an impact on other species. The result is a ripple effect across the entire ecosystem.

Video 1: Phenology and ‘mismatches’ in nature.
Fig. 1:  Plants and animals evolved to behave in certain ways, like migrating or laying eggs, because of seasonal cues. Some species react to the length of the day; others to temperature. Before the climate began changing, the timing of events was in balance.
Fig. 1: Plants and animals evolved to behave in certain ways, like migrating or laying eggs, because of seasonal cues. Some species react to the length of the day; others to temperature. Before the climate began changing, the timing of events was in balance.
Fig. 2: Now that temperatures are rising, some but not all plants and animals are being cued to behave differently. This is called 'phenological mismatch', that is, the timing of events is 'mismatched'. Some species may starve, like the baby birds in Fig. 1,  while others, like leaf-eating caterpillars grow into plague numbers and eat too much, killing plants. This is damaging for both natural environments and also farmers and gardeners.

Fig. 2: Now that temperatures are rising, some but not all plants and animals are being cued to behave differently. This is called ‘phenological mismatch’, that is, the timing of events is ‘mismatched’. Some species may starve, like the baby birds in Fig. 1, while others, like leaf-eating caterpillars grow into plague numbers and eat too much, killing plants. This is damaging for both natural environments and also farmers and gardeners.

Example 2 species on the move: As the climate warms, some plants and animals that evolved to live on cooler climates are migrating to either higher altitudes or latitudes. In many places they can’t move because there is nowhere for them to go, for example, cities and farms are in the way.

In the ocean more tropical fish are now being seen in the waters around New Zealand while some sea creatures are heading in the wrong direction:

“In the northwest Atlantic Ocean, slow-moving snails, sand dollars, mussels and other creatures with drifting larvae are spawning earlier, triggered by warmer seas. Unfortunately, that’s when winds and currents are aligned to drive them into even hotter waters. The result is that the ranges of once-abundant species are shrinking.”  Science, 2020

Example 3 losing pollinators: If a plant species flowers earlier because the days are warmer, but the migratory bird species that feeds and pollinates it migrates according to the length of the day, the bird won’t arrive in time to pollinate the flower or feed off its nectar. The plant won’t be pollinated and the bird also goes hungry, so both are at risk. If the plant is a food crop it may become scarce or even die out.

Example 4 too many boys and not enough girls: (Fig. 3).

Fig. 3: Tuatara eggs generally produce 50% male and 50% female hatchlings. An increase in temperatures of just 1°C means that 80% of the hatchlings are male. Ad the world has already warmed 1°2C that has profound implications for the species unless it can move to cooler locations. (Image: Sid Mosdell / CC BY 2.0)

Example 5 too hot for flowers (and fruit) to form:

Temperatures fluctuate all the time, so many plants that have adapted to flower in spring take their cue from long periods of cold weather followed by warm weather, ie, a cold winter rather than a few cold days or weeks. Having adapted to the cold, some are no longer flowering in Spring because the winter wasn’t cold enough. No flowers means they can’t be pollinated by bees, and they won’t produce seeds or fruit. If this happens every year, eventually the entire species will die out as it can’t reproduce.

Fig. 4: Many plant species won’t flower in the spring unless they have experienced a long period of cold weather. If the plant doesn’t flower, it won’t be fertilised so it won’t produce seeds or fruit. (Image: Nature)

Natural ecosystems are more resilient to change because they are composed of a high diversity of species that evolved by ‘survival of the fittest’. They don’t depend on endless amounts of artificial fertilisers or pesticides, so while some species will be lost, if they can migrate to cooler climates (either by going higher up mountains or further south), or in the case of coastal ecosystems by moving inland as sea levels rise, they will quickly adapt.

However, natural ecosystems in New Zealand are so fragmented that unless they can take to the air or swim the ocean, few species can move.

This also poses a problem for those restoring ecosystems: should they plant what used to be there by eco-sourcing local seeds and plants? Or should they also include natives plants from warmer climates, especially long lived plants like trees, which will have ti survive a warming world in the coming decades?

References and further reading