Changing weather patterns are disrupting hard-wired animal and plant reproduction systems with unpredictable consequences for biodiversity.
In the northern hemisphere, climate change is causing spring to arrive earlier. We know this from reliable climate records dating back to 1880 and in some cases earlier than that. Herbarium records are turning out to be a huge source of important plant data.
Plants and animals have adapted to relatively stable climate conditions over hundreds of years, even millennia. If average temperatures rise by half a degree Celsius in 100 years – the blink of an eye in evolutionary terms – many species may struggle to adapt in time.
Several recent phenology studies – the study of how plant and animal life cycles are influenced by seasonal variations in climate – have been exploring this issue and their findings are casting a light on the interlinkage between climate change and the animal world.
Students at Fort Lewis College in Colorado in the United States of America reviewed herbarium records spanning a 122-year period and found a four-to five-day shift in average flowering. Lower elevation plants had a mean flowering time 15 days earlier than in the 1890s, whereas upper elevation plants had only a three-day shift.
This has consequences for insects, birds and other animals that depend on plants in one way or another. Many plants require insects or animals to pollinate them, but if they flower too early, the pollinators might not be there in sufficient numbers for the plants to effectively reproduce themselves.
Earlier flowering times might bring flowers out of sync with their pollinators. If insect pollinators also develop earlier, will migrating birds that arrive later and feed on the insects be affected?
In the United Kingdom, scientists have discovered that great tit chicks no longer hatch soon enough to coincide with peak supplies of their crucial caterpillar food. Another study in central England looked at 356 years of temperature records and found that warmer temperatures are upsetting the seasonal relationship between the early spider orchid and pollinating bees.
Caribou in western Greenland eat lichen along the coast. In the spring and summer, they venture inland to give birth to their calves and eat the plants that grow there. But as Greenland has warmed, those inland plants have been emerging earlier, meaning that by the time they get there most of the caribou’s food has gone, according to a study conducted in the Arctic.
Migrating barnacle geese, the subject of another Arctic study, are being prompted by warming weather and snowmelt to speed up migration to their northern nesting sites. To do so they are skipping a vital food stopover, leaving them weakened and with goslings less able to survive.
Insects may fare worse in adapting
Insects are the most diverse group of animals on Earth, but there is little information about their fate in a changing climate. Some research suggests they may fare worse than other species: a recent study found that for vertebrates and plants, the number of species losing more than half their geographic range by 2100 is halved when warming is limited to 1.5°C, compared with projected losses at 2°C. For insects, the number is reduced by two-thirds.
Such evidence highlights that climate change affects the geographic ranges of species and biodiversity in ways we don’t yet understand.
“Species react differently to climate change, which disrupts the delicate interaction between them,” says Niklas Hagelberg, a UN Environment Climate Change and Ecosystems Expert based in Nairobi, Kenya. “This further complicates conservation; we need to quickly add climate change to our ecosystem management effort.”
Meanwhile, the findings in these reports should give pause for thought as the Global Climate Action Summit kicks off in San Francisco tomorrow.