TEMPERATE & TROPICAL VARIATION IN ECOLOGICAL SPECIALIZATION
The climate that characterizes tropical regions across the globe is generally warm, wet, and stable. Proximity to the equator means these areas do not experience large swings in temperature, nor do they experience significant seasonal change. The amount of rainfall the tropics receive largely determines the two main seasons of the year - wet and dry. Because precipitation shapes the dynamics of tropical ecosystems, these regions of the world have not experienced great environmental variation across time.
Since tropical biomes have remained fairly stable over millennia, it is hypothesized that animals that evolved in these regions could depend on predictable resources, which allowed them to specialize and occupy narrower environmental niches. Further, it has also been predicted that climatic stability allowed tropical animals to develop narrow physiological tolerances. Physiological specialization leads to behavioral specialization that leads to ecological specialization, and vice versa. In birds, a lot of work has been done on testing the hypothesized "slow pace of life" that typifies birds living in the tropics. Compared with temperate birds, tropical birds have slower metabolic rates, expend less energy, mature slower, and live longer. Unlike their temperate counterparts, tropical birds are also not limited with a short time window in which to breed; given the relatively mild conditions of the tropics, birds can capitalize on favorable conditions for more months of the year.
Since tropical biomes have remained fairly stable over millennia, it is hypothesized that animals that evolved in these regions could depend on predictable resources, which allowed them to specialize and occupy narrower environmental niches. Further, it has also been predicted that climatic stability allowed tropical animals to develop narrow physiological tolerances. Physiological specialization leads to behavioral specialization that leads to ecological specialization, and vice versa. In birds, a lot of work has been done on testing the hypothesized "slow pace of life" that typifies birds living in the tropics. Compared with temperate birds, tropical birds have slower metabolic rates, expend less energy, mature slower, and live longer. Unlike their temperate counterparts, tropical birds are also not limited with a short time window in which to breed; given the relatively mild conditions of the tropics, birds can capitalize on favorable conditions for more months of the year.
In stark contrast, temperate regions are marked by regular, seasonal change. From January to December, ecosystems such as the boreal forest undergo complete transformation —from a moist, buggy, and warm environment over the summer, reminiscent of some tropical rain forests—to a seemingly barren, snow-covered landscape that withstands temperatures that can plummet to -60°F and lower. Such tremendous environmental change has selected for animals to have wide ecological niches that allow them to tolerate considerable physiological extremes.
Compared to tropical birds, temperate birds can be thought of as living in the fast lane. Because favorable conditions only last from about May to August, temperate birds have a much shorter period of time to complete breeding activities. This limitation is even further compounded for birds that are migratory, who also need to incorporate travel and layover time at least two times into their annual activities. As a result of these challenges, many temperate birds develop quickly, operate at a faster pace, and live shorter lives.
Compared to tropical birds, temperate birds can be thought of as living in the fast lane. Because favorable conditions only last from about May to August, temperate birds have a much shorter period of time to complete breeding activities. This limitation is even further compounded for birds that are migratory, who also need to incorporate travel and layover time at least two times into their annual activities. As a result of these challenges, many temperate birds develop quickly, operate at a faster pace, and live shorter lives.
While some work has been done on the physiological specialization of tropical birds compared to temperate birds, we know relatively little on how tropical birds may specialize differently in both their behavior and environment. While climatic stability has contributed to specialized physiological niches among tropical forest birds, it is likely that these climatic pressures have also selected for differences in behavior over multiple temporal and spatial scales. Large differences exist between some temperate and tropical birds in their life history strategies (e.g., migratory vs. sedentary, large clutches vs. small clutches, etc.), but more subtle differences in characteristics such as diurnal cycles, movements, and foraging strategies may also be present.
To better understand how tropical birds compare to temperate birds in their ecological specialization, we are investigating the behavior of a variety of temperate-tropical species pairs breeding at separate sites in South Carolina and Panama. Comparing across 18 different species, we have recorded several behavioral and ecological observations, including foraging rate, movement rate, substrate and heights at which birds conducted activities, and other attributes. This study is an ongoing collaborative effort with Henry Pollock as part of work on thermal sensitivities of understory insectivorous birds.
To better understand how tropical birds compare to temperate birds in their ecological specialization, we are investigating the behavior of a variety of temperate-tropical species pairs breeding at separate sites in South Carolina and Panama. Comparing across 18 different species, we have recorded several behavioral and ecological observations, including foraging rate, movement rate, substrate and heights at which birds conducted activities, and other attributes. This study is an ongoing collaborative effort with Henry Pollock as part of work on thermal sensitivities of understory insectivorous birds.