What is ecology? • Ecology is the study of the interactions of organisms with one another and with their physical environment. • Biosphere - part of the Earth in which life exists. • Includes land, air, and water as well as life. • Living organisms are NOT distributed uniformly throughout the biosphere.
The biosphere is large… • …So ecoslgists work with smaller units called ecosystems. • Ecosystem - consists of an area’s physical features and living organisms. • Abiotic factors - physical features • Ex. elevation, humidity, rainfall • Biotic factors - living organisms • Ex. snails, worms, plants, insects
Members of ecosystems are related • Community - all the populations of organisms living in a given area. • Ecosystems rarely function independently of one another because they are connected by both living and non living features.
Ecological succession • Ecological succession - an existing community of organisms is replaced by a different community over time. • Can occur where no living community existed before (like a volcano arising from the sea). • Can also occur following a dramatic change (like a forest fire). • Succession leads to a collection of organisms called a climax community. • Biome - an environment that has a characteristic climax community.
Energy flow through ecosystems • Of all the sun’s energy the reaches the Earth’s surface, only about 0.1% is used by living things. • Energy cannot be recycled or used again! • For this reason, we refer to the movement of energy through an ecosystem as a flow, not a cycle.
Energy flows through ecosystems • The sun is the ultimate source of energy for living things. • Producers - organisms that make their own food via photosynthesis. • Consumers - organisms that get their energy directly or indirectly from producers. • Primary consumers - also called herbivores; plant eating animals. • Secondary consumers - animals that eat primary consumers. • Energy flows through an ecosystem from the sun to producers and then to consumers.
Energy flows through ecosystems • Herbivores - organisms that eat plants. • Carnivores - organisms that eat animals. • Omnivores - organisms that eat plants and animals. • Decomposers - organisms that obtain energy from non-living organic matter.
Energy flows through ecosystems • Trophic level - each step in a series of organisms eating other organisms. • At each higher trophic level, less and less of the energy originally captured by the producers is available. • This is because the energy obtained from digested food is used to maintain metabolism. • Only about 10% of the energy from one trophic level can be used by the animals at the next trophic level!
Nutrients are recycled through an ecosystem • While energy moves in a one-way direction through an ecosystem, nutrients are recycled and used again and again. • Biogeochemical cycle - nutrients use these processes to move through the biosphere. • Ex. Water, carbon, nitrogen, oxygen cycles
Nutrients are recycled through an ecosystem - Water cycle • Water cycle - movement of water between the atmosphere and Earth. • Consists of alternating cycles of evaporation and condensation. • Evaporation moves water molecules into the air while precipitation returns it to Earth. • Some water sinks into the ground (groundwater) while some runs along the surface of the ground until it enters a river or stream.
Nutrients are recycled through an ecosystem - Nitrogen cycle • Nitrogen - element required by living organisms to build proteins. • Nitrogen cycle - movement of nitrogen through biosphere. • Most can’t be used directly by living organisms - it must be converted into more usable forms.
Nutrients are recycled through an ecosystem - Nitrogen cycle • Nitrogen fixation - performed by bacteria that live on the roots of some plants - change free nitrogen in the atmosphere into nitrogen compounds (nitrates and nitrites). • Denitrification - bacteria in the soil break down nitrogen compounds into free nitrogen that is returned to the atmosphere.
Nutrient limitation • The rate at which producers can capture energy is limited by the amount of available nutrients. • Limiting factor - the nutrient that is in short supply that limits an organism’s growth.
Ecosystem relationships • Food chain - simplest feeding relationship linking animals and plants in the biosphere. • Usually contains 3-5 total organisms.
Ecosystem relationships • Food web - complex relationship formed by interconnecting and overlapping food chains.