Biologists find increasing evidence that the appearance and behaviour of animals and plants in the wild are changing under the influence of global warming. For example, plants start flowering earlier, animals may breed or migrate at different times than they did in the past, and the average body size of some animal species has decreased over past generations. It is less obvious, however, whether such changes also have an impact on the viability of these populations; in other words, whether they may lead to population declines or, conversely, represent adaptations that help populations counteract environmental changes.

In a new study, a global dataset comprising more than 200 long-term field studies on various bird, reptile, mammal, and fish species was analysed, with a focus on changes in the timing of breeding or migration, and changes in body size or weight. Overall, climate warming had stronger effects on timing than on morphology. Moreover, the study showed that these changes in timing (such as earlier breeding in warmer years) contributed positively to population growth, thereby countering the potential negative effects of climate warming; as a consequence, most of the studied species were able to maintain their population sizes over decades. Species in more northern regions responded more strongly to temperature changes over time, but there remains considerable variation among species that could not be easily explained by general species characteristics.

For UAntwerpen, Erik Matthysen contributed to the study. The EVECO team has decades of experience in phenological responses of bird populations to changing environmental conditions.

                  Changes in timing of breeding of great tit (squares) and blue tits (circles) near Antwerp.