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Climate Effects on Species Concept 52.4: Interactions between organisms and the environment limit the distribution of species • Species distributions are the result of ecological and evolutionary interactions through time • Ecological time is the minute-to-minute time frame of interactions between organisms and the environment • Evolutionary time spans many generations and captures adaptation through natural selection • Events in ecological time can lead to evolution • For example, Galápagos finches with larger breaks were more likely to survive a drought as they could eat the available larger seeds • As a result, the average beak size was larger in the next generation • This resulted in an evolutionary change • Both biotic and abiotic factors influence species distribution – For example, temperature, water availability, and interspecific interactions, affect the distribution of the saguaro cacti Figure 52.15 ARIZONA CALIFORNIA BAJA CALIFORNIA SONORA BAJA CALIFORNIA SUR GULF OF CALIFORNIA N 100 km Sonoran desert Saguaro cacti observed Figure 52.15a • Ecologists ask questions about where species occur and why species occur where they do Figure 52.16-1 Why is species X absent from an area? Does dispersal limit its distribution? Figure 52.16-2 Why is species X absent from an area? Yes Does dispersal limit its distribution? No Area inaccessible or insufficient time Does behavior limit its distribution? Figure 52.16-3 Why is species X absent from an area? Yes Does dispersal limit its distribution? No Area inaccessible or insufficient time Does behavior limit its distribution? Yes No Habitat selection Do biotic factors (other species) limit its distribution? Figure 52.16-4 Why is species X absent from an area? Yes Does dispersal limit its distribution? No Area inaccessible or insufficient time Does behavior limit its distribution? Yes No Habitat selection Do biotic factors (other species) limit its distribution? Yes No Predation, parasitism, competition, disease Do abiotic factors limit its distribution? Figure 52.16-5 Why is species X absent from an area? Yes Does dispersal limit its distribution? No Area inaccessible or insufficient time Does behavior limit its distribution? Yes Habitat selection No Do biotic factors (other species) limit its distribution? Yes No Water, Oxygen, Salinity, pH, Soil nutrients, etc. Temperature, Light, Soil structure, Fire, Moisture, etc. Chemical factors Physical factors Predation, parasitism, competition, disease Do abiotic factors limit its distribution? Dispersal and Distribution • Dispersal is the movement of individuals or gametes away from centers of high population density or from their area of origin • Dispersal contributes to the global distribution of organisms Natural Range Expansions and Adaptive Radiation • Natural range expansions show the influence of dispersal on distribution – For example, cattle egrets arrived in the Americas in the late 1800s and have expanded their distribution • In rare cases, long-distance dispersal can lead to adaptive radiation – For example, Hawaiian silverswords are a diverse group descended from an ancestral North American tarweed Figure 52.17 Current 1970 1966 1965 1960 1961 1958 1943 1951 1956 1970 1937 Figure 52.17a Species Transplants • Species transplants include organisms that are intentionally or accidentally relocated from their original distribution • If a transplant is successful, it indicates that its potential range is larger than its actual range • 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 • Biotic factors that affect the distribution of organisms may include – Predation – Herbivory • For example, sea urchins can limit the distribution of seaweeds – Competition – Mutualism – Parasitism Figure 52.18 Sea urchin Limpet Seaweed cover (%) 100 80 Both limpets and urchins removed 60 Only urchins removed 40 Only limpets removed 20 0 August 1982 Control (both urchins and limpets present) February 1983 August 1983 February 1984 Figure 52.18a Sea urchin Figure 52.18b Limpet Abiotic Factors • Abiotic factors affecting the distribution of organisms include – Temperature – Water – Oxygen – Salinity – Sunlight – Soil • Most abiotic factors vary in space and time Temperature • Environmental temperature is an important factor in the 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 and Oxygen • Water availability in habitats is another important factor in species distribution • Desert organisms exhibit adaptations for water conservation • Water affects oxygen availability as oxygen diffuses slowly in water • Oxygen concentrations can be low in deep oceans and deep lakes Salinity • Salt concentration affects the water balance of organisms through osmosis • Most aquatic organisms are restricted to either freshwater or saltwater habitats • Few terrestrial organisms are adapted to high-salinity habitats • Salmon are able to migrate between freshwater and ocean Sunlight • Light intensity and quality (wavelength) affect photosynthesis • Shading by leaves makes competition for light intense on the forest floor • Water absorbs light; as a result, in aquatic environments most photosynthesis occurs near the surface • In deserts, high light levels increase temperature and can stress plants and animals Figure 52.19 Rocks and Soil • Many characteristics of soil limit the distribution of plants and thus the animals that feed on them – Physical structure – pH – Mineral composition Figure 52.UN03a Data from the Field Experiment Average Biomass (g/100 cm2) Spartina patens Typha angustifolia Salt Marshes Freshwater Marshes Salt Marshes Freshwater Marshes With neighbors 8 3 0 18 Without neighbors 10 20 0 33 Figure 52.UN03b Data from the Greenhouse Experiment 0 20 40 60 80 100 % maximum biomass (Spartina patens) 77 40 29 17 9 0 % maximum biomass (Typha angustifolia) 80 20 10 0 0 0 Salinity (parts per thousand Figure 52.UN03c Spartina patens Figure 52.UN03d Typha angustifolia Figure 52.UN04 Does dispersal limit its distribution? Yes Area inaccessible or insufficient time No Does behavior limit its distribution? Yes Habitat selection No Do biotic factors (other species) limit its distribution? No Do abiotic factors limit its distribution? Yes Predation, parasitism, competition, disease Chemical factors: Water, oxygen, salinity, pH, soil nutrients, etc. Physical factors: Temperature, light, soil structure, fire, moisture, etc. Figure 52.UN05 Altitude (m) Mean height (cm) Figure 52.UN06 75 50 25 0 3,000 2,000 Sierra Nevada 1,000 0 Seed collection sites Great Basin Plateau Figure 52.UN07