Ecology The scientific study of the interactions

Ecology

The scientific study of the interactions between organisms and their environments is called ecology (from the Greek iokos, home, and logos, to study)

• There are two questions ecologists try to answer. • What factors limit the geographic range, or distribution, of species? • What factors determine its abundance?

Biotic Factors § Living factors in an organism’s environment Abiotic Factors § Nonliving factors in an organism’s environment § Organisms adapt to survive in the abiotic factors present in their natural environment.

Levels of Organization § Levels increase in complexity as the numbers and interactions between organisms increase. § organism § population § biological community § ecosystem § biome § biosphere

The Biosphere § A thin layer around Earth § Extends several kilometers above the Earth’s surface § Extends several kilometers below the ocean’s surface

The Biosphere

§ The lowest level of organization is the individual organism itself. § Organisms of a single species that share the same geographic location at the same time make up a population. § A biological community is a group of interacting populations that occupy the same geographic area at the same time.

§ An ecosystem is a biological community and all of the abiotic factors that affect it. § A biome is a large group of ecosystems that share the same climate and have similar types of communities.

Ecosystem Interactions § A habitat is an area where an organism lives. § A niche is the role or position that an organism has in its environment.

Community Interactions § Competition § Occurs when more than one organism uses a resource at the same time § Predation § Many species get their food by eating other organisms.

Symbiotic Relationships § The close relationship that exists when two or more species live together § Mutualism § Commensalism § Parasitism

Mutualism (+/+) • A kind of symbiotic nutrition in which both organisms benefit. • Ex: Aphids & ants CO , H O Lichen FUNGI ALGAE Food, O 2 2 2

Commensalism (+/0) • A kind of symbiotic nutrition in which one organism benefits and the other one is neither harmed nor helped. • Example barnacles that attach to a whale

Parasitism (+/-) • A kind of symbiotic nutrition in which one organism benefits (parasite) and the other one (host) is harmed. PARASITE External Internal They live on the body -Louse They live in the body -Ascaris

Flow of Energy in an Ecosystem § Autotrophs § Organism that collects energy from sunlight or inorganic substances to produce food § Heterotrophs § Organism that gets it energy requirements by consuming other organisms

§ Detritivores eat fragments of dead matter in an ecosystem, and return nutrients to the soil, air, and water where the nutrients can be reused by organisms. Fungus

Models of Energy Flow § Food chains and food webs model the energy flow through an ecosystem. § Each step in a food chain or food web is called a trophic level.

Food Chains § A food chain is a simple model that shows how energy flows through an ecosystem.

Food Webs § A food web is a model representing the many interconnected food chains and pathways in which energy flows through a group of organisms.

Ecological Pyramids § A diagram that can show the relative amounts of energy, biomass, or numbers of organisms at each trophic level in an organism

Biotic Factors

• Negative interactions: with other organisms in the form of predation, parasitism, or competition. • Alternatively, survival and reproduction may be limited by the absence of other species on which the transplanted species depends, such as pollinators for many flowering plants. • Humans…

Abiotic Factors • Physical conditions. • Most abiotic factors vary in space and time (daily and annual fluctuations). • Furthermore, organisms can avoid some stressful conditions temporarily through behaviors such as dormancy or hibernation.

Temperature • Environmental temperature is an important factor in the distribution of organisms because of its effect on biological processes. • Cells may rupture if the water they contain freezes (at temperatures below 0°C), and the proteins of most organisms denature at temperatures above 45°C.

• Most organisms function best within a specific range of environmental temperature. (optimum) • Temperatures outside that range may force some animals to expend energy regulating their internal temperature, as mammals and birds.

Water • The dramatic variation in water availability among habitats is another important factor in species distribution. • Species living at the seashore or in tidal wetlands can desiccate (dry out) as the tide recedes. • Terrestrial organisms face a nearly constant threat of desiccation, and the distribution of terrestrial species reflects their ability to obtain and conserve water. • Desert organisms, for example, exhibit a variety of adaptations for acquiring and conserving water in dry environments.

Salinity • The salt concentration of water in the environment affects the water balance of organisms through osmosis. • Most aquatic organisms are restricted to either freshwater or saltwater habitats by their limited ability to osmoregulate. • Although many terrestrial organisms can excrete excess salts from specialized glands or in feces, salt flats and other high-salinity habitats typically have few species of plants or animals.

Sunlight • Sunlight absorbed by photosynthetic organisms provides the energy that drives most ecosystems, and too little sunlight can limit the distribution of photosynthetic species. • In forests, shading by leaves in the treetops makes competition for light especially intense, particularly for seedlings growing on the forest floor. • In aquatic environments, every meter of water depth selectively absorbs about 45% of the red light and about 2% of the blue light passing through it. • As a result, most photosynthesis in aquatic environments occurs relatively near the surface.

• Too much light can also limit the survival of organisms. • The atmosphere is thinner at higher elevations, absorbing less ultraviolet radiation, so the sun's rays are more likely to damage DNA and proteins in alpine environments. • In other ecosystems, such as deserts, high light levels can increase temperature stress if animals are unable to avoid the light or to cool themselves through evaporation.

Rocks and Soil • The p. H, mineral composition, and physical structure of rocks and soil limit the distribution of plants and thus of the animals that feed on them. • The p. H of soil and water can limit the distribution of organisms directly, through extreme acidic or basic conditions, or indirectly, through the solubility of nutrients and toxins. • In streams and rivers, the composition of the bottom surface can affect water chemistry, which in turn influences the resident organisms.

HW • Examples