Ecologists study life at many levels, from individual organism to the entire biosphere.
Ecology: “eco” means house “ology”means study of.
Levels of organizationCells – Tissue-Organs – Organ systems -Organisms
Population – a group of individuals of the same species that live in the same area at a given time
Example: a group of white-tailed deer in an oak-hickory forest in southeastern PA
Community - groups of living organisms that interact with one another in a particular area.
Example: deer, mice, bushes and snakes in the forest community
Ecosystem: a community together with its physical environment
Biosphere: all parts of the earth that hosts life, with all of its organisms and environments.
Ecosystems include both biotic and abiotic factors. Biotic factors are parts of the ecosystem that are living.
Abiotic factors are parts of the ecosystem that are non-living.
Biotic factors:
Abiotic:
Organisms depend on resources provided by their habitat for survival.
The specific environment in which an organism lives is its habitat.
A habitat provides an organism with resources. A resource is anything an organism needs to survive.
Describing Populations….
The OVERALL health of a population can often be monitored by tracking how its size changes.
Population size describes the number of individual organisms present in a given population at a given time.
Population Ecology
Deals with the # of individuals of a particular species that are found in an area and how and why those numbers change or remain fixed over time.
Population ecologists study…
How populations respond to its environment
Competition for resources, predations, disease and other environmental pressures
Determine population size by sampling. Instead of counting every individual, ecologists count every organism in a small area than estimate the number of individuals in the larger area.
Population density describes the number of individuals within a population per unit area.
For example: 1500 golden toads per 4 sq. kilometers
In general, larger animals have lower population density because they need more resources.
High population density can make it easier to find mates and group together. However, it also leads to more competition for resources.
Overcrowded organisms can also lead to increase of disease and vulnerable to predators.
Age structure diagrams show the number of males & females in different age groups within a population.
Age structure describes the relative number of organisms of each age with in a population.
Age structure diagrams are a visual tool to show the age structure of populations.
Stable – approximately the same number of individuals at each age grouping, mix of young and old
Growing – mostly young
Declining – the largest portion of population is older
A population’s growth rate is determined by births, deaths, immigration and emigration.
All things being equal, when a population birthrate is greater than its death rate, population size will increase.
When death rate is greater than its birth rate, population size will decrease.
In addition to births & deaths, population size can also change by individuals moving in & out.
Immigration – movement of individuals into a populationEmigration – movement of individuals into a population
Birthrate – number of live births per 1000 in a given yearDeath rate – number of deaths per 1000 in a given year
CALCULATING GROWTH RATE
Growth rate (r) = birth rate (b)+ I – death rate (d) + E
Population growth is typically reported as a net change per 1000 individuals.
Exponential growth is when a population increases by a fixed percentage each year.