As spring arrives, albeit quite late this year for many of us, we notice the changing of seasons by the weather, but also by a host of natural events. Depending on where you live, the crocuses may poke through the snow the killdeer may be back, or the cherry trees may bloom. There is an orderly sequence of events that seem to occur, with various spring flowers appearing in order, red maple buds bursting into new leaves, or the old lilac by the barn scenting the air. This seasonal cycle of natural phenomena is called phenology. Global climate change appears to be interfering with the phenology of many species, at the very heart of species interactions.
In temperate regions like the northern half of the United States , there is comparatively little biological activity in winter. Most plants are dormant , and so are the insects feeding on them. In turn , animals that rely on these Insects , such as bats and birds, are hibernating or spending the cold months in more southerly locations. Ectotherms like reptiles and amphibians, which take their body warmth from their environment , also have active phases tied to the seasons. This long winter period constrains all the growing, breeding, and dispersing activities that plants and animals do to a short favorable window. That’s what makes spring so vibrant, with plants flowering and putting on new growth, insects emerging and breeding, and birds flying back to take advantage of this short-lived bounty. The onsets of each of these activities add up to so many phenological markers.
Different organisms respond to different cues to initiate seasonal activities. Many plants will start growing leaves again after a set period of dormancy, which very roughly dictates the leaf-out window. Cue that more precisely determine when the buds break can be soil temperature, air temperature, or water availability. Similarly, temperature cues can promote the beginning of insect activity. Day length itself can be the operative trigger for some seasonal events. It is only when there are a sufficient number of daylight hours that reproductive hormones will be produced in many bird species.
The most energy-demanding period in the life of most animals is when they reproduce. For that reason , it is to their advantage to coincide breeding (and for many, the raising of young) during a period when food is most abundant. Caterpillars should hatch just as the young tender leaves of oak tree emerge, before they harden and become less nutritious. Breeding songbirds need to time the hatching of their young just during that peak in caterpillar activity, so they can take advantage of this rich source of protein to feed their offspring. Many species have evolved to exploit peaks in resource availability, so all these seemingly independent phenological events are indeed part of a complex web of precise interactions. Disruptions in seasonal events can have profound effects on ecosystems. (http://environment.about.com/)
The ideas in the passage may be best summarized that ...