Concept 52.2: Interactions between organisms and the environment limit the distribution of species Ecologists have long recognized global and regional patterns of distribution of organisms within the biosphere Biogeography is a good starting point for understanding what limits geographic distribution of species Ecologists recognize two kinds of factors that determine distribution: biotic, or living factors, and abiotic, or nonliving factors

Kangaroos/km2 0–0.1 0.1–1 1–5 5–10 10–20 > 20 Limits of Fig. 52-5 Kangaroos/km2 0–0.1 0.1–1 1–5 5–10 10–20 > 20 Limits of distribution Figure 52.5 Distribution and abundance of the red kangaroo in Australia, based on aerial surveys

Ecologists consider multiple factors when attempting to explain the distribution of species

Figure 52.6 Flowchart of factors limiting geographic distribution Why is species X absent from an area? Yes Area inaccessible or insufficient time Yes Does dispersal limit its distribution? Habitat selection Yes Predation, parasitism, competition, disease Does behavior limit its distribution? Chemical factors No Do biotic factors (other species) limit its distribution? Water Oxygen Salinity pH Soil nutrients, etc. No Do abiotic factors limit its distribution? No Temperature Light Soil structure Fire Moisture, etc. Physical factors Figure 52.6 Flowchart of factors limiting geographic distribution

Dispersal and Distribution Dispersal is movement of individuals away from centers of high population density or from their area of origin Dispersal contributes to global distribution of organisms

Natural Range Expansions Natural range expansions show the influence of dispersal on distribution

Fig. 52-7 Current 1970 1966 1965 1960 1961 1958 1943 1937 1951 1956 Figure 52.7 Dispersal of the cattle egret in the Americas 1970

Species Transplants Species transplants include organisms that are intentionally or accidentally relocated from their original distribution Species transplants can disrupt the communities or ecosystems to which they have been introduced

Behavior and Habitat Selection Some organisms do not occupy all of their potential range Species distribution may be limited by habitat selection behavior

Biotic factors that affect the distribution of organisms may include: Interactions with other species Predation Competition

August 1982 February 1983 August 1983 February 1984 Fig. 52-8 RESULTS 100 Both limpets and urchins removed 80 Sea urchin Only urchins removed 60 Seaweed cover (%) Limpet 40 Figure 52.8 Does feeding by sea urchins limit seaweed distribution? Only limpets removed 20 Control (both urchins and limpets present) August 1982 February 1983 August 1983 February 1984

Abiotic factors affecting distribution of organisms include: Temperature Water Sunlight Wind Rocks and soil Most abiotic factors vary in space and time

Temperature Environmental temperature is an important factor in distribution of organisms because of its effects on biological processes Cells may freeze and rupture below 0°C, while most proteins denature above 45°C Mammals and birds expend energy to regulate their internal temperature

Water Water availability in habitats is another important factor in species distribution Desert organisms exhibit adaptations for water conservation

Salinity Salt concentration affects water balance of organisms through osmosis Few terrestrial organisms are adapted to high-salinity habitats

Sunlight Light intensity and quality affect photosynthesis Water absorbs light, thus in aquatic environments most photosynthesis occurs near the surface In deserts, high light levels increase temperature and can stress plants and animals

Fig. 52-9 Figure 52.9 Alpine tree

Rocks and Soil Many characteristics of soil limit distribution of plants and thus the animals that feed upon them: Physical structure pH Mineral composition

Climate Four major abiotic components of climate are temperature, water, sunlight, and wind The long-term prevailing weather conditions in an area constitute its climate Macroclimate consists of patterns on the global, regional, and local level Microclimate consists of very fine patterns, such as those encountered by the community of organisms underneath a fallen log

Global Climate Patterns Global climate patterns are determined largely by solar energy and the planet’s movement in space Sunlight intensity plays a major part in determining the Earth’s climate patterns More heat and light per unit of surface area reach the tropics than the high latitudes

Figure 52.10 Global climate patterns Fig. 52-10a Latitudinal Variation in Sunlight Intensity 90ºN (North Pole) 60ºN Low angle of incoming sunlight 30ºN 23.5ºN (Tropic of Cancer) Sun directly overhead at equinoxes 0º (equator) 23.5ºS (Tropic of Capricorn) 30ºS Low angle of incoming sunlight 60ºS 90ºS (South Pole) Atmosphere Seasonal Variation in Sunlight Intensity 60ºN 30ºN March equinox 0º (equator) June solstice 30ºS Figure 52.10 Global climate patterns Constant tilt of 23.5º December solstice September equinox

Low angle of incoming sunlight Fig. 52-10b 90ºN (North Pole) 60ºN Low angle of incoming sunlight 30ºN 23.5ºN (Tropic of Cancer) Sun directly overhead at equinoxes 0º (equator) 23.5ºS (Tropic of Capricorn) 30ºS Figure 52.10 Global climate patterns Low angle of incoming sunlight 60ºS 90ºS (South Pole) Atmosphere

Seasonal variations of light and temperature increase steadily toward the poles

60ºN 30ºN March equinox 0º (equator) June solstice 30ºS Fig. 52-10c 60ºN 30ºN March equinox 0º (equator) June solstice 30ºS Figure 52.10 Global climate patterns December solstice Constant tilt of 23.5º September equinox

Global air circulation and precipitation patterns play major roles in determining climate patterns Warm wet air flows from the tropics toward the poles

Global Air Circulation and Precipitation Patterns Fig. 52-10d Global Air Circulation and Precipitation Patterns 60ºN 30ºN Descending dry air absorbs moisture Descending dry air absorbs moisture 0º (equator) Ascending moist air releases moisture 30ºS 60ºS 30º 23.5º 0º 23.5º 30º Arid zone Tropics Arid zone Global Wind Patterns 66.5ºN (Arctic Circle) 60ºN Westerlies Figure 52.10 Global climate patterns 30ºN Northeast trades Doldrums 0º (equator) Southeast trades 30ºS Westerlies 60ºS 66.5ºS (Antarctic Circle)

Arid zone Tropics Arid zone Fig. 52-10e 60ºN Descending dry air absorbs moisture Descending dry air absorbs moisture 30ºN 0º (equator) Ascending moist air releases moisture 30ºS 60ºS 30º 23.5º 0º 23.5º Figure 52.10 Global climate patterns 30º Arid zone Tropics Arid zone

Air flowing close to Earth’s surface creates predictable global wind patterns Cooling trade winds blow from east to west in the tropics; prevailing westerlies blow from west to east in the temperate zones

66.5ºN (Arctic Circle) 60ºN Westerlies 30ºN Northeast trades Doldrums Fig. 52-10f 66.5ºN (Arctic Circle) 60ºN Westerlies 30ºN Northeast trades Doldrums 0º (equator) Southeast trades 30ºS Figure 52.10 Global climate patterns Westerlies 60ºS 66.5ºS (Antarctic Circle)

Regional, Local, and Seasonal Effects on Climate Proximity to bodies of water and topographic features contribute to local variations in climate Seasonal variation also influences climate

Bodies of Water The Gulf Stream carries warm water from the equator to the North Atlantic Oceans and their currents and large lakes moderate the climate of nearby terrestrial environments

Labrador current Gulf stream Equator water Warm Cold water Fig. 52-11 Figure 52.11 The great ocean conveyor belt Cold water

During the day, air rises over warm land and draws a cool breeze from the water across the land As the land cools at night, air rises over the warmer water and draws cooler air from land back over the water, which is replaced by warm air from offshore

Warm air over land rises. Fig. 52-12 Air cools at high elevation. 2 Cooler air sinks over water. 3 Warm air over land rises. 1 Cool air over water moves inland, replacing rising warm air over land. 4 Figure 52.12 Moderating effects of a large body of water on climate

Mountains have a significant effect on The amount of sunlight reaching an area Local temperature Rainfall Rising air releases moisture on the windward side of a peak and creates a “rain shadow” as it absorbs moisture on the leeward side

Wind direction Mountain range Fig. 52-13 Leeward side of mountain Wind direction Mountain range Figure 52.13 How mountains affect rainfall Ocean

Seasonality The angle of the sun leads to many seasonal changes in local environments Lakes are sensitive to seasonal temperature change and experience seasonal turnover

Microclimate Microclimate is determined by fine-scale differences in the environment that affect light and wind patterns

Long-Term Climate Change Global climate change will profoundly affect the biosphere One way to predict future global climate change is to study previous changes As glaciers began retreating 16,000 years ago, tree distribution patterns changed As climate changes, species that have difficulty dispersing may have smaller ranges or could become extinct

Current range Predicted range Overlap (a) 4.5ºC warming over Fig. 52-14 Current range Predicted range Figure 52.14 Current range and predicted range for the American beech (Fagus grandifolia) under two scenarios of climate change Overlap (a) 4.5ºC warming over next century (b) 6.5ºC warming over next century