Populations and Community Ecology Chapters 19 & 20

Population Dynamics A population is defined as the number of individuals in one particular species in a particular place, at a given time. For example: The population of zebras in Kenya in the year 1980 Population density : The number of organisms per unit of land area or ocean volume

Population: a group of living things of the same species that live in an area.  A change in the size of one population often causes a change in the size of another population.

Factors that affect population size Mortality Natality Emigration Immigration

Measuring the size of a population Census Sampling Tag and release

Ways to count populations: Radio transmitter Ear Tags Ribbons (Paint) Leg bands

Symbiosis Organisms of different kinds living together in the same ecosystem Any of the following relationships are considered to be symbiotic: - Predator – prey - Parasite – host - Commensalism - Mutualism - Pathogen - host

Predator - Prey Lions and zebras, for example One hunts and kills, the other gets killed and eaten

Parasite - Host Fleas and dogs for example The parasite harms the host and benefits from the relationship. The host is harmed, but not usually killed

Pathogen - Host E.coli H.I.V. A pathogen is a disease-causing agent, like a bacterium or a virus H.I.V. E.coli

Mutualism A symbiotic relationship where two organisms are in a mutually beneficial relationship Examples: Lichens are not one organism but two – an algae and a fungus living as one. The algae provides the fungus with glucose in return for moisture from the fungus. Clown Fish are protected from predator fish by the stinging tentacles of the anemone. The anemone receives protection from polyp-eating fish, like Butterfly Fish, which the Clown Fish chases away. The anemone also gets fertilizer from the feces of the Clown Fish.

Commensalism In this relationship, one organism benefits but the other is neither harmed nor benefited Examples: Shark and remora,

More unusual examples of animal symbiosis

Carrying Capacity The maximum number of individuals of a particular species that an ecosystem can support without depleting its resources These are two types of population growth curves – one shows exponential growth (unrestricted) and the other logistic growth (restricted)

Predator-Prey cycle

Limiting Factors Any abiotic factor that limits the survivability of organisms in a particular ecosystem is called a limiting factor Examples: Water in a desert, light in the deepest parts of the ocean (abyssal and benthic zones), etc.

Limiting Factors Any condition that keeps the size of a population from increasing. Due to a lack of: Space Light Food Water

Communities All of the living things in an area that depend upon each other.

HABITAT A place where a plant or animal lives. It provides the organism with: place to reproduce water food shelter

Types of Habitats Beaver Dam Spider Web African Plains

Niche The job of an organism within the community.

Species Dispersal When a species occupies an uninhabited area and settles there, it colonizes this new area A species that is native to an area is considered an indigenous species A species that is new to an already occupied area is called an exotic species Lichens are colonizers Kangaroos are indigenous to Australia The mongoose is an exotic species to Hawaii – imported from India, it is decimating certain indigenous bird species

Succession Ecosystems are unstable – they change constantly due to fire, extinction, climate change and other causes New communities replace the old – this process of constant change of communities is called succession Succession can begin either on bare rock in a lake or pond and eventually give rise to a mature forest

Succession on bare rock (Primary Succession) Annuals and perennials Lichens can break down rocks by producing acids like carbonic acid that slowly dissolve the rock minerals.

Succession on a lake bed (Primary Succession) Each year trees and shrubs along the edge of a lake shed leaves and debris into the water that then settle to the bottom. This debris slowly decays to form new habitat for grasses, rushes and sedges. The grasses take root quickly and stabilize the new ground for dry land species. Some day shrubs and small trees will grow where lily pads once floated. As the lake becomes smaller and smaller, it may not be able to provide enough oxygen or food for some fish. But this happens so slowly that they have plenty of time to move on to other lakes, if the lake is connected to the rest of the watershed by a stream.

Primary succession on a volcanic island

Succession on burned or disturbed land (Secondary Succession)

A climax temperate deciduous forest community Climax Community Once succession has progressed to a point where no new species can fit into the community, it is called a climax community A climax Chaparral community A climax prairie community A climax temperate deciduous forest community

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