Bird Reproduction And Global Warming

Two examples elucidate the complexity of understanding changes to inter-species patterns of relationship and, thus, comprehending the complexity of the changes that global warming introduces to ecosystems. One example comes from the United Kingdom and concerns relations between flower blooming, butterfly production of caterpillars, and bird reproduction. For 47 years, naturalist Richard Fitter wrote down notes about the flowering times of many plant species, the arrival and reproduction of birds, and the life cycles of butterflies that he observed around his house and garden. In 2001, his son Alistair Fitter, an ecologist, analyzed these detailed data in order to assess what they might reveal about the potential impact of global warming on patterns of relationships within ecological systems.

He also sought to determine the extent to which such an impact might bear significant consequences in regard to the sustainability of interdependent species. The results, published in Science in 2002, were astoundingly informative. They were subsequently confirmed by research conducted under the auspices of the Intergovernmental Panel on Climate Change that same year, and by other independent researchers around the world.

This research shows that as late as 1980, the hatching food-needs of birds matched the peak mass of the quantity of caterpillars that were available within that ecosystem. In other words, the patterns of reproduction for these two interdependent species were coupled in time. By 2002, however, these patterns had been decoupled as a result of global warming and the onset of a sequence of years marked by a two-week earlier arrival of spring.

By 2002, the birds had maintained their average date for laying eggs (April 23) and their date for hatching (May 15), which marked the beginning of a two-week period where birds were in the highest demand for the caterpillars to feed their offspring. The birds' peak demand for nutrition, which in 1980 had corresponded with peak availability in caterpillar mass, continued to be on May 28. By 2002, however, caterpillars displayed different hatching dates, most likely related to an earlier arrival of spring temperatures, as well as to the consequent early blooming of flowers. The peak mass of caterpillar availability in 2002 was May 15, almost two weeks earlier than in previous decades. It is for this reason that ecologists say that the two species are now decoupled.

This example points toward four dimensions of the complexity implicit in the challenge of understanding the effects of global warming and climate change on ecosystems. First, it indicates that responses to the temperature variations that come with global warming are relative and peculiar to each species within an ecosystem. Some species, such as flowers and butterflies, seem to have a lower threshold for sensing temperature variation and respond accordingly by blooming and reproducing earlier in the season. Species such as birds, by contrast, seem less sensitive to temperature variations and continue to produce offspring at the same time as before.

Second, this example shows that a comprehensive understanding of the impact of increased global warming can be neither based on a discussion of absolute values, nor on the effects that such variations might have for a single species in an ecosystem. The full appreciation of the effects that global warming has on ecosystems must be based on an analysis of the extent to which, and the ways in which, this phenomenon affects relationship patterns among species.

A third dimension that must be considered in assessing the effects of global warming is that there are complex interactions between different ecosystems. Ecosystems do not exist autonomously and the sustainability of one ecosystem often depends on interactions with other ecosystems. This is particularly true of ecosystems that are connected through migratory species, such as ecosystems spanning from Central America to Canada, which rely on monarch butterflies for pollination. In addition, ecosystems are frequently nested within wider ecosystems such that their resiliency depends on complex interactions across different spatial scales.

Finally, this example shows that understanding the effects of global warming on ecosystems requires a temporally-extended view of the patterns that connect these different species, which are crucial elements in their long-term sustainability. It was only by means of analyzing the data that Richard Fitter collected over a period of 47 years that the decoupling of reproducing patterns of flowers, butterflies, and birds became visible.

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