Earth's Timeline

Geography

Examines patterns in order to discover the underlying processes that govern their behavior.

Biogeography

The study of the distribution of species and ecosystems in geographic space and through geological time.

Central questions of biogeography

Which species occur where, why do they occur there, and why are they absent from other places?

Why is "Why not?" important in biogeography?

Understanding why a species is absent from a location can reveal environmental, geographic, historical, or biological factors that limit its distribution.

Geological time

The immense span of Earth's history through which the evolution and geographic distribution of life can be studied.

Age of Earth

The course timeline places the formation of Earth at approximately 4.55 billion years ago.

Age of the Moon

The course timeline places the formation of the Moon at approximately 4.527 billion years ago.

Cambrian explosion

A major event in the history of life shown on the course timeline at approximately 530 million years ago.

Snowball Earth events

The course timeline identifies two major Snowball Earth events occurring approximately 750–635 million years ago.

First vertebrate land animals

The course timeline places the first vertebrate land animals at approximately 380 million years ago.

Dinosaurs

The course timeline places dinosaurs approximately between 230 and 65 million years ago.

First hominids

The course timeline places the first hominids at approximately 2 million years ago.

Why is geological time important to biogeography?

Species distributions are influenced not only by present-day conditions but also by evolutionary and geological history.

Solar energy

The principal origin of energy for life on Earth.

Total solar energy

Varies by latitude.

Latitude

The geographic position north or south of the Equator; differences in latitude produce differences in the amount of solar energy received.

Why does latitude matter to biogeography?

Latitude influences solar energy and temperature, which helps shape geographic patterns of species and ecosystems.

Mean annual temperature

The average temperature of a location over the course of a year.

Global temperature pattern

Mean annual temperature generally decreases from lower latitudes toward higher latitudes.

Biomes

Large ecological regions characterized by distinctive combinations of climate, vegetation, and associated organisms.

Global biomes

Major biome types distributed geographically across Earth according to environmental conditions.

Tropical rain forest

A global biome associated with warm and wet tropical conditions.

Tropical seasonal forest/savanna

A tropical biome associated with seasonal differences in moisture.

Subtropical desert

A very dry biome found primarily in subtropical regions.

Temperate grassland/desert

A biome category associated with temperate climates and relatively dry conditions.

Woodland/shrubland

A biome characterized by woody vegetation and shrubs and occurring in relatively dry or seasonally dry environments.

Temperate seasonal forest

A biome found in temperate regions characterized by seasonal changes in climate and vegetation.

Temperate rain forest

A biome characterized by relatively cool temperate conditions and high precipitation.

Boreal forest

A forest biome occurring primarily at high northern latitudes.

Tundra

A cold biome occurring at high latitudes, particularly toward the Arctic.

Alpine

A biome associated with high-elevation mountainous environments.

Ice cap

A biome category associated with areas dominated by permanent ice.

Species

A biological category used to describe organisms; species and their geographic distributions are central subjects of biogeography.

Species distribution

The geographic area in which a species occurs.

Species range

The geographic extent occupied by a species.

Historic range

The geographic area in which a species occurred historically.

Present range

The geographic area in which a species currently occurs.

Historic vs. present range

Comparing historic and present ranges can reveal how a species' geographic distribution has changed over time.

Grizzly bear range example

The course uses the grizzly bear to illustrate the difference between a species' historic range and its present range.

Main range

The principal portion of a species' geographic distribution.

Discontinuous range

A species distribution in which populations occur in separated areas rather than forming one continuous range.

Isolated populations

Populations separated geographically from the main range or from one another.

Metapopulations

A set of spatially separated populations of the same species.

Extirpated populations

Populations that have disappeared from a particular geographic area even though the species may still exist elsewhere.

Temporary populations

Populations or occurrences that are not necessarily persistent or reproductively established.

Individual adults not reproducing

Individuals can occur outside the main reproductive distribution of a species without representing an established population.

Why is a species' range more complicated than simply "where it lives"?

A species may have a main range, discontinuous populations, isolated populations, extirpated populations, and temporary or nonreproducing individuals.

Predation

An ecological interaction in which one organism consumes another.

Population dynamics

Changes in the size or abundance of populations through time.

Predator-prey population pattern

Predator and prey populations can fluctuate through time in cyclical patterns.

Predator-prey cycles

Changes in prey abundance can influence predator abundance, while changes in predator abundance can subsequently influence prey abundance.

Keystone species

A species that plays a major role in maintaining the structure and integrity of an ecological community.

Keystone species analogy

A keystone in an arch helps hold the other stones in place; similarly, a keystone species helps maintain the structure of an ecological community.

Why are keystone species important?

Removing or substantially changing a keystone species can affect the structure and integrity of the broader ecological community.

Biodiversity

The variety of life represented by the many different forms and lineages of organisms.

Evolution

A core concept used to explain how biological diversity arose and changed through time.

Genetic drift

A core evolutionary mechanism identified in the course as contributing to evolutionary change.

Natural selection

A core evolutionary mechanism identified in the course through which differences in survival and reproduction can influence evolutionary change.

Speciation

The formation of new species.

Four core concepts in evolution theory

Evolution, genetic drift, natural selection, and speciation.

Allopatric speciation

The formation of new species through geographic isolation.

Geographic isolation

Separation of populations by a geographic barrier that prevents or limits gene flow between them.

Geographic barrier

A physical geographic separation that divides a population and restricts interaction or gene flow.

Sequence of allopatric speciation

An original population becomes geographically separated; the populations diverge while isolated; reproductive isolation develops; secondary contact may occur; and selection against hybrids can contribute to formation of distinct species.

Incipient species

Populations beginning to diverge into separate species.

Reproductively isolated populations

Populations that can no longer successfully exchange genes through reproduction.

Secondary contact

A stage in which populations that became geographically isolated come back into geographic contact.

Low-fitness hybrids

Hybrids with reduced reproductive success or fitness.

Selection against hybrids

Natural selection can favor individuals that avoid producing low-fitness hybrids, contributing to reproductive divergence.

Speciation in the allopatric diagram

Geographic isolation can initiate divergence that ultimately results in two distinct species.

Adaptive radiation

When a single lineage rapidly diversifies into a variety of related forms specialized to fit different niches.

Niche

The ecological role or way of life associated with a species, including how it uses environmental resources.

Adaptive radiation and niches

Adaptive radiation occurs when descendants of one lineage become specialized for different ecological niches.

Galápagos finches

The course uses Galápagos finches as an example of adaptive radiation, showing related finches associated with different ecological resources and forms.

Why does adaptive radiation produce multiple species?

A lineage can diversify as different populations become specialized for different ecological opportunities or niches.

Convergent evolution

The evolution of similar characteristics in organisms that are not closely related, often because they experience similar environmental or selective pressures.

Convergent evolution example

The course shows several rodents and one marsupial with similar body forms despite their different evolutionary histories.

Why can unrelated organisms look similar?

Similar environmental conditions and selective pressures can lead unrelated lineages toward similar adaptations through convergent evolution.

Species-area relationship

A biogeographic relationship in which larger islands generally support more species than smaller islands.

Large islands and species richness

Large islands support more species than small islands.

Species richness

The number of different species occurring in a particular area.

Evidence for the species-area relationship

The relationship has been observed in case study after case study.

Species-area graph

The number of species increases with area, with the relationship shown as a curved increase when species and area are plotted on their original scales.

Log-log species-area graph

Plotting the logarithm of species and the logarithm of area produces a more linear relationship.

Why are islands important in biogeography?

Islands provide clear geographic areas for studying how area relates to species richness and distribution.

Homo sapiens

The scientific species name for modern humans.

Human evolution

Fossil records and molecular biology indicate that Homo sapiens evolved approximately 200,000 years ago, according to the course slide.

Fossil record

Evidence from preserved remains of organisms that can be used to study the history and evolution of life.

Molecular biology evidence for human evolution

Molecular evidence, together with fossil evidence, is used to understand the evolutionary history of Homo sapiens.

Human population growth

The course's human population graph shows relatively slow population growth for much of human history followed by a dramatic increase in recent centuries.

Human population graph period

The course graph covers approximately 10,000 BCE through 2100 CE.

Agricultural society and human-environment relationships

The course notes that approximately 200 years ago, about 70% of people in the United States would have been farmers.

Urbanization

The increasing concentration of people in urban areas.

Urban vs. rural population

The course's urbanization graph shows the global share of people living in urban areas increasing while the rural share decreases over time.

Human population and biogeography

Changes in human population size and settlement patterns alter relationships between humans, ecosystems, resources, and other species.

Globalization

The course shows extensive global connections associated with movement of people and goods between regions.

Global shipping

Container shipping is presented as an example of the scale of human movement and global economic connections.

Shipping and environmental impact

The course presents container shipping as a major source of pollution and CO2 emissions.

Human-caused environmental change

Human activities can alter atmospheric composition, climate, habitats, species distributions, and ecological systems.

Atmospheric carbon dioxide and global temperature

The course graph shows atmospheric carbon dioxide increasing alongside a strong increase in average global temperature, especially in recent decades.