Environmental Variation

Physical conditions vary seasonally in most biomes (see Fig. 2.5). Temperate ecosystems are characterized by obvious seasonality in temperature, with cooler winters and warmer summers, and also may show distinct seasonality in precipitation patterns, resulting from seasonal changes in the orientation of Earth's axis relative to the sun. Although tropical ecosystems experience relatively consistent temperatures, precipitation often shows pronounced seasonal variation (see Fig. 2.5). Aquatic habitats show seasonal variation in water level and circulation patterns related to seasonal patterns of precipitation and evaporation. Seasonal variation in circulation patterns can result in stratification of thermal layers and water chemistry in lotic systems. Intermittent streams and ponds may disappear during dry periods or when evapotranspiration exceeds precipitation.

Physical conditions also vary through time as a result of irregular events. Changes in global circulation patterns can affect biomes globally. For example, the east-west gradient in surface water temperature in the southern Pacific diminishes in some years, altering oceanic and atmospheric currents globally— the El Niño/southern oscillation (ENSO) phenomenon (Rasmussen and Wallace 1983, Windsor 1990). The effect of ENSO varies among regions. Particularly strong El Niño years (e.g., 1982-1983 and 1997-1998) are characterized by extreme drought conditions in some tropical ecosystems and severe storms and wetter conditions in some higher latitude ecosystems. Seasonal patterns of precipitation can be reversed (i.e., drier wet season and wetter dry season).The year following an El Niño year may show a rebound, an opposite but less intense, effect (La Niña). Windsor (1990) found a strong positive correlation between El Niño index and precipitation during the preceding year in Panamá. Precipitation in Panamá usually is lower than normal during El Niño years, in contrast to the greater precipitation accompanying El Niño in Peru and Ecuador (Windsor 1990, Zhou et al. 2002).

Many insects are sensitive to the changes in temperature and moisture that accompany such events. Stapp et al. (2004) found that local extinction of black-tailed prairie dog, Cynomys ludovicianus, colonies in the western Great Plains of North America was significantly greater during El Niño years as a result of flea-transmitted plague, Yersinia pestis, which spreads more rapidly during warmer, wetter conditions (Parmenter et al. 1999). Similarly, Zhou et al. (2002) reported that extremely high populations of sand flies, Lutzomyia verrucarum, were associated with El Niño conditions in Peru, resulting in near doubling of human cases of bartonellosis, an emerging, vectorborne, highly fatal infectious disease in the region (Fig. 2.7).

Solar activity, such as solar flares, may cause irregular departures from typical climatic conditions. Current changes in regional or global climatic conditions also may be the result of deforestation, desertification, fossil fuel combustion and other anthropogenic factors that affect albedo, global circulation patterns and atmospheric concentrations of CO2, other greenhouse gases, and particulates. Characteristic ranges of tolerance to climatic factors determine the seasonal,

Environmental Changes Affect PlantsEnvironmental Changes Affect PlantsAquatic Biome Temperature Images

Seasonal variation in temperature and precipitation at sites representing major biomes. Data from van Cleve and Martin (1991).

Seasonal variation in temperature and precipitation at sites representing major biomes. Data from van Cleve and Martin (1991).

latitudinal, and elevational distributions of species and potential changes in distributions as a result of changing climate.

Terrestrial and aquatic biomes differ in the type and extent of variation in physical conditions. Terrestrial habitats are sensitive to changes in air temperature, wind speed, relative humidity, and other atmospheric conditions. Aquatic habitats are relatively buffered from sudden changes in air temperature but are sensitive to changes in flow rate, depth, and chemistry, especially changes in pH and concentrations of dissolved gases, nutrients, and pollutants. Vegetation cover insulates the soil surface and reduces albedo, thereby reducing diurnal and seasonal variation in soil and near-surface temperatures. Hence, desert biomes with

Pond Biome

| Examples of aquatic biomes. A: Stream (western United States), B: beaver pond (western United States), C: swamp (southern United States), D: coastal saltmarsh (southeastern United States), E: lake (Hungary). Coastal saltmarsh photo (D) courtesy of S. D. Senter.

Enviroment Variation

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Trmm Cusco

| Topography of Peru (center), comparison of TRMM (tropical rainfall measuring mission) TMI (tropical rainfall measuring mission microwave imager) rainfall at Cuzco (lower left) and Caraz (upper right) relative to their surroundings, and the sand fly, Lutzomyia verrucarum, vector of bartonellosis that shows increased spread associated with higher rainfall during El Niño events. Strong association of precipitation at Cuzco with monsoon system makes local sand fly abundance sensitive to El Niño events, whereas precipitation at Caraz, within the equatorial convergence zone, leads to more consistent abundance of sand flies. From Zhou et al. (2002) with permission from the American Geophysical Union. Please see extended permission list pg 569.

| Topography of Peru (center), comparison of TRMM (tropical rainfall measuring mission) TMI (tropical rainfall measuring mission microwave imager) rainfall at Cuzco (lower left) and Caraz (upper right) relative to their surroundings, and the sand fly, Lutzomyia verrucarum, vector of bartonellosis that shows increased spread associated with higher rainfall during El Niño events. Strong association of precipitation at Cuzco with monsoon system makes local sand fly abundance sensitive to El Niño events, whereas precipitation at Caraz, within the equatorial convergence zone, leads to more consistent abundance of sand flies. From Zhou et al. (2002) with permission from the American Geophysical Union. Please see extended permission list pg 569.

sparse vegetation cover usually show the widest diurnal and seasonal variation in physical conditions. Areas with high proportions of impervious surfaces (such as roads, roofs, parking lots) greatly alter conditions of both terrestrial and aquatic systems by increasing albedo and precipitation runoff (Elvidge et al. 2004).

Physiological tolerances of organisms, including insects, generally reflect the physical conditions of the biomes in which they occur. Insects associated with the tundra biome tolerate a lower range of temperatures than do insects associated with tropical biomes. The upper threshold temperature for survival of a tundra species might be the lower threshold temperature for survival of a tropical species. Similarly, insects characterizing mesic or aquatic biomes generally should have less tolerance for desiccation than do insects characterizing xeric biomes.

However, species characterizing temporary streams or ponds may have adapted mechanisms for withstanding desiccation during dry periods (Batzer and Wissinger 1996). Some species show greater capacity than others do to adapt to changing environmental conditions, especially rapid changes resulting from anthropogenic activity. Such species may be predisposed to adapt to rapid changes because of evolution in frequently disturbed ecosystems.

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  • BROGAN
    What is the temperature in aquatic biome?
    6 years ago

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