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54 Ecology and the Distribution of Life • Ecology • The scientific study of interactions between organisms and their environment. • It is a relatively new branch of science, with roots in Darwin’s The Origin of Species. As Haeckel explained: “Ecology is the study of all those complex interrelations referred to by Darwin as ‘the conditions of the struggle for existence.’” Why Study Ecology? • Human activities can profoundly affect our environment • We need data on the consequences of our activities. • Ecological understanding improves: • our ability to grow food sustainably • managing pests and diseases • dealing with natural disasters • avoiding unintended consequences for ourselves and other organisms “Ecology” is not equivalent to “environmentalism.” Ecology is a science that generates knowledge about interactions in the natural world. Environmentalism is the use of this knowledge (with economics, ethics, etc.), to inform personal decisions and public policy relating to stewardship of natural resources and ecosystems. • Ecology encompasses 2 components: • Biotic – living • Abiotic - Nonliving • New Tools to study Ecology: • mathematical models • molecular techniques • satellite imaging Weather and Climate • • • Weather is the short-term state of atmospheric conditions at a particular place and time. Climate refers to average atmospheric conditions, over a longer time. “Climate is what you expect, weather is what you get!” Organisms and their Climate Organism responses to climate tend to be adaptations that affect physiology, morphology, and behavior. These adaptations are among the forces driving speciation over evolutionary time. Why do Climates Vary? • Differences in solar energy • • Temperature decreases with elevation Movement of air • Due to angle of sun’s rays • Tilt of Earth on axis • Warm air rises (i.e. at the equator) • The air cools and is no longer able to hold moisture • precipitation • As it descends, the cool air starts to warm and take up moisture • Look at figure at where air is descending – this is where we find the Earth’s deserts • This results in global air circulation and prevailing winds Figure 54.2 Air Circulation in Earth’s Atmosphere • Rotation of Earth influences the movement of air masses produced by global air circulation • Results in prevailing winds • Deflected to right in Northern Hemisphere • Left in Southern Hemisphere Global air circulation is what drives ocean currents Organisms and their environment • Organisms must adapt to climatic challenges • Metabolic specializations • Behavioral specializations Adaptations of organisms • Organisms may produce antifreezes to deal with low temps • Limits damage to cells • Rounded shapes and short appendages to reduce surface area • Reduce heat loss • • Pigmentation Behavioral changes • “sunning”, looking for shelter • Migration to new area Biome • Biome • An environment defined by its climatic and geographic attributes • characterized by its dominant plants. • provide three- dimensional structure • modify microclimates near the ground • strongly influence other organisms living there. Figure 54.5 The Global Distribution of Biomes Biome • • • General descriptions of the biomes cannot describe all the variation existing in each. Boundaries between biomes are somewhat arbitrary; in many places biomes merge into one another. Recognizing the major biomes is useful because these environments share ecological attributes irrespective of their location. Tundra: • Location: • Arctic • high elevations • • • Vegetation is low-growing perennials. permafrost Animals migrate or go dormant for much of the year. Boreal forest (taiga): Long, cold winters; short summers • Dominated by evergreens in the Northern Hemisphere— can start photosynthesis quickly in the short growing season. • Only a few tree species • Dominant mammals, (e.g., moose and hares) eat leaves. • Temperate evergreen forests: • Location: • Along coasts of continents at mid to high latitudes. • Winters are mild but wet; summers are cool and dry. Temperate deciduous forest: • • • Precipitation is distributed evenly, but temperatures fluctuate dramatically. Dominated by deciduous trees that lose leaves during the cold season. Some animals migrate to avoid cold season (e.g., songbirds), others hibernate Temperate grasslands: • • • Dry much of the year; hot summers and cold winters. Rich in species; grasses, sedges, and forbs. Plants are adapted to grazing and fire. Much of this biome has been converted to agriculture. The topsoil is deep and rich. Hot desert: • • • • In two belts at 30°N and 30°S More species and more structurally diverse vegetation than cold deserts. Plants have many adaptations to dry conditions. Succulents are common. Many annuals grow only after a rainfall. Small animals stay in burrows during the day; many get water only from their food. Cold desert: • In continental interiors and rain shadows. • Dominated by few species—lowlying shrubs. Plant growth mostly occurs in spring. • Plants produce lots of seed that supports seed-eating birds and rodents. • Animals burrow to escape cold temperatures. Chaparral: • On western sides of continents with cool ocean currents offshore. • Winters are cool and wet, summers warm and dry. • Adapted to fire. • Shrubs and low trees with tough, evergreen leaves Thorn forest and tropical savanna: At latitudes below the hot deserts • Little rain in winter; but may be heavy in summer. • Small trees may drop leaves in dry winter • Savannas—grasslands with scattered trees; supports large grazing and browsing mammals and large predators. • Tropical deciduous forest: • • • Most trees lose leaves during the dry season; many flower while they are still leafless. Most of the plants are pollinated by animals, and are important “refueling” stops for migratory birds. Most have been cleared for agriculture and cattle grazing. Tropical evergreen forest (rainforest): • • • Equatorial regions with high rainfall. Highest species richness of all biomes. Up to 500 tree species per km2. Also highest overall productivity. Most nutrients are tied up in vegetation; soils are poor. Florida Combination of biomes – unique areas ○ Temperate deciduous forest ○ Tropical deciduous forest ○ Aquatic biomes Everglades unique area Biogeographic Regions Evolutionary history is influenced by geological history • Alfred Russel Wallace – 1800s • traveled extensively in the Malay Archipelago • noticed remarkable patterns of distribution of organisms • striking differences in biota from one island to the next that could not be explained by differences in geology or climate - the islands were identical • drew a line through the archipelago based on distributions of plants and animals • He deduced that the differences had to do with the depth of water separating the two regions • It remained a barrier even during Pleistocene glaciations when sea level dropped more than 100 m. Biogeographic Regions • Earth can be divided into biogeographic regions, each containing characteristic species assemblages. • Boundaries occur where species composition changes dramatically over short distances. • The regions have barriers to dispersal between • Mountains • oceans, etc. • A species found only in a certain region is said to be endemic to that region. • Remote islands tend to have endemic biotas because water greatly restricts dispersal. • Madagascar has many endemic species. • Biodiversity hotspot Biogeographic Regions Causes of the distribution of species were only speculated upon until two scientific advances occurred: Acceptance of the theory of continental drift Development of phylogenetic taxonomy • About 280 million years ago, the continents were united into one land mass • Pangea • • During the Triassic period, the supercontinent Pangaea broke apart. Many groups of terrestrial and freshwater organisms had already evolved. Geologic events can also bring land masses together. Land bridges can form, for instance, when ocean levels drop • A vicariant event • Appearance of a physical barrier that splits the range of a species • Dispersal • if organisms cross an existing barrier and establish a population • Both result in discontinuous ranges. • Studies can show which once caused an observed distribution • Human activity is another force capable of generating unusual distribution patterns • Many species have been introduced to new regions; some have been deliberate, some not • Many introductions have resulted in disaster—diseases of crops and animals, household pests, etc. Ocean ~70% surface of the Earth is covered by ocean Contains as much as 99% of the biosphere! There is MUCH we still do not know about the ocean ○ What will be our impact on it? Ocean Life Zones • Ranges of marine organisms are restricted by water temperature, salinity, and food supply, which all vary spatially. • Oceans can be divided into distinct “life zones.” • They are identified mainly in relation to water depth and light penetration. Ocean • Photic zone • enough light to support photosynthesis • Coastal zone • extends from the shoreline to the edge of the continental shelf • characterized by shallow, well-oxygenated water and stable temperatures and salinities • Littoral Zone – affected by wave action • Intertidal Zone – affected by the tides • Pelagic Zone • Open ocean • Benthic Zone • Ocean sediment Figure 54.14 Oceanic Life Zones Ocean • Dominant Autotrophs • Phytoplankton – photosynthetic protists • In the open ocean, or pelagic zone, the principal consumers are zooplankton— mainly small crustaceans and larval stages of marine animals. Ocean • Aphotic Zone • Depths reached by less than 1 percent of incoming sunlight • Organisms in this region subsist on decaying organic matter that sinks down from the photic zone • Some produce their own light in bioluminescent organs • In deep-ocean trenches and rift valleys, ecosystems are often sustained by chemosynthetic microbes • can metabolize the nutrients in seawater without the aid of sunlight • “chemosynthesis” in hydrothermal vents • Freshwater environments • running water (streams and rivers) • standing water (lakes and ponds) Lakes can be divided into life zones similar to those in the oceans • Although freshwater environments cover less than 3% of Earth’s surface they are home to about 10% of all aquatic species • Most animals that live in fresh water cannot survive in ocean water, which can limit dispersal. Most freshwater fish species are restricted to one continent because they can’t tolerate salt water (can’t disperse). • Estuaries form where rivers meet the ocean, and salt water mixes with fresh water • They have many unique species • play an important role for other species as a conduit between marine and freshwater environments • Ocean’s “nurseries”