-Directional Selection, which drives a feature in one direction. - Stabilizing Selection, which favors intermediate traits. - Disruptive Selection, which traits diverge in two or more directions.
Unrelated species may evolve similar traits because they live in similar environments.
The process of selection conducted under human direction
Biological Diversity (Biodiversity)
The variety of life across all levels of biological organization: - species - genes - populations - communities
The process of generating new species
Species formation due to physical separation of populations. This is the main mode of speciation.
Species form populations that become reproductively isolated within the same area.
- Feed in different areas - Mate in different seasons - Hybridization between two species - Mutations
Phylogenetic Trees (cladograms)
Show relationships among species, groups, and genes. Scientists can trace how certain traits evolved.
An imprint in stone of a dead organism
The cumulative body of fossils worldwide
The disappearance of species from Earth. Species last 1 to 10 million years.
Equation to find the number of species
Speciation minus extinction
Extinction is a natural process, BUT...
...humans profoundly affect rates of extinction and biodiversity loss affects people directly.
When does extinction occur?
When the environment changes rapidly and Natural Selection cannot keep up.
Name a few more causes of Extinction
- Severe weather, climate change, changing in sea levels - New species, small populations - Specialized species
A species only exists in a certain, specialized area.
Background Extinction Rate
Extinction usually occurs one species at a time.
Mass Extinction Events
Killed off massive numbers of species at once.
Cretaceous - Tertiary Event
Dinosaurs went extinct 65 Million years ago
75-95% of all species went extinct 250 million years ago
How are we causing the 6th mass extinction event?
- Resource depletion, population growth, development - Destruction of natural habitats
The total living things on Earth and the areas they inhabit.
Interacting species living in the same area
Communities and the nonliving material and the forces they interact with.
Investigates the dynamics of population change and the factors affecting the distribution and abundance of members of a population and why some populations increase and others decrease.
Studies living and nonliving components of systems to reveal patterns and to see how nutrient and energy flows.
the environment where an organism lives, including living and nonliving things.
Each organism thrives in certain habitats, but not others.
The process by which organisms actively select habitats in which to live
An organism's use of resources. This term can also refer to the organism's functional role in a community, it's habitat use, food selection, role in energy and nutrient flow, and interactions with other individuals.
Have narrow niches and specific needs. Extremely good at what they do, but vulnerable when conditions change.
Species with broad niches. They use a wide array of habitats and resources and can live in many different places.
The number of individual organisms present at a given time.
Number of individuals in a population per unit area. There are "low" and "high" densities
For large organisms, who need many resources and a large area to survive. It is more difficult to find a mate with less organisms due to lack of space which is caused my the size of the organisms.
Easier to find mates, but there is an increase in competition and vulnerability to predation. There is also an increased transmission of diseases.
Population Distribution (dispersion)
Special arrangement of organisms:
- Random Distribution - Uniform Distribution - Clumped Distribution
Haphazardly located individuals and there is no pattern.
Individuals evenly spaced. This distribution includes territoriality and competition.
Arranged according to availability of resources. This distribution is the most common in nature.
proportion of males to females
Age Distribution (structure)
the relative numbers of organisms of each age in a population. Displayed in an "Age Structure diagram" (pyramid).
the likelihood of death varies with age
Type I: more deaths at older ages Type II: Equal number of deaths at all ages Type III:more deaths at younger ages
Births within the population
Deaths within the population
Arrival of individuals outside of the population. Adds to number of individuals
Departure of individuals from the population. Subtracts from number of individuals.
Crude birth (death) rates
number of births (deaths) per 1000 individuals per year