Unit 2 Beta

The Living World: Biodiversity: the one-page sheet

2.1 Introduction to Biodiversity

Biodiversity is variety at three levels: genes within a population, species within a community, and habitats within an area. Species diversity combines richness (how many species) and evenness (how equal they are). More diverse populations and ecosystems usually recover better from stress, a bottleneck leaves a population with little genetic diversity, and a keystone species holds its community together.

Biodiversity has three levels: genetic diversity (variety of genes in a population), species diversity (variety of species in a community) and habitat diversity (variety of habitats in an area).
Species diversity has two parts: species richness, the number of different species, and species evenness, how equal their population sizes are. More of either means more diversity.
A population bottleneck is a sharp drop in population size. The survivors carry only part of the original gene variety, so genetic diversity stays low even after numbers recover.
A keystone species has a much larger effect on its community than its numbers suggest; removing it changes the whole community.

there are more different traits and more species that can do each job in the ecosystem some individuals or species are likely to survive it, because they differ from the ones that are hurt the population or ecosystem recovers faster than a less diverse one would

biodiversity: The variety of life in an area, measured at three levels: genetic diversity within populations, species diversity within communities, and habitat diversity within an area.
genetic diversity: The variety of genes (and so of heritable traits) among the individuals of one population or species. High genetic diversity makes it more likely that some individuals survive a new disease or a change in conditions.
species richness: The number of different species in a community or area.
species evenness: How equal the population sizes of the species in a community are. A community where each species has similar numbers is even; one dominated by a single species is uneven.
habitat diversity: The variety of different habitats (forest, meadow, stream, wetland) in an area. More habitat diversity supports more species. Also called ecosystem diversity.
population bottleneck: A sharp drop in the size of a population, for example from hunting, a disease or a disaster. The few survivors carry only part of the original genetic diversity, so the population stays genetically less diverse even if its numbers recover.
keystone species: A species whose effect on its community is much larger than its numbers suggest. Removing it changes the structure of the whole community, as when sea urchins multiply and strip kelp forests after sea otters disappear.

2.2 Ecosystem Services

Ecosystem services are the benefits people get from working ecosystems: provisioning (goods such as food, timber and water), regulating (pollination, water purification, flood control, carbon storage), cultural (recreation, tourism, beauty) and supporting (photosynthesis, nutrient cycling, soil building). Damaging an ecosystem removes services that then cost money to replace.

An ecosystem service is a benefit people get from a working ecosystem. There are four kinds: provisioning, regulating, cultural and supporting.
Provisioning services are goods people take: food, fish, timber, fresh water, medicines. Regulating services are natural processes that protect people: pollination, purifying water, controlling floods, storing carbon.
Cultural services are nonmaterial benefits: recreation, tourism, beauty, spiritual value, education. Supporting services keep the other three going: photosynthesis, nutrient cycling, soil formation, habitat.
Disrupting an ecosystem has costs that a price tag often leaves out: the lost services must be paid for some other way.

people receive goods (food, wood, water) and protection (clean water, flood control, a steadier climate) at no charge the services it gave are reduced or lost there is an ecological cost and an economic cost that the original decision did not count

ecosystem services: A benefit that people receive from a working ecosystem, such as clean water, food, pollination or recreation. Ecosystem services are grouped into four kinds: provisioning, regulating, cultural and supporting.
provisioning services: An ecosystem service that provides goods people take and use: food, fish, timber, fiber, fresh water and medicines.
regulating services: An ecosystem service that comes from natural processes keeping conditions stable for people: pollination of crops, purification of water, control of floods and erosion, and storage of carbon.
cultural services: An ecosystem service that provides nonmaterial benefits: recreation, tourism, beauty, spiritual value and opportunities for education and research.
supporting services: An ecosystem service that the other services depend on: photosynthesis, nutrient cycling, soil formation and providing habitat.

2.3 Island Biogeography

Island biogeography explains species richness on islands: larger islands hold more species because fewer species die out there, and islands nearer the mainland hold more because more colonists arrive. The same rules apply to habitat fragments, which act like islands, so breaking up a habitat into small, isolated patches lowers the number of species it can keep.

Island biogeography studies how many species islands hold and why. Larger islands hold more species, and islands closer to the mainland hold more species.
Distance sets how often new species arrive: far islands get fewer colonists. Size sets how often species die out: small islands have fewer habitats and smaller populations, so more species are lost.
Habitat fragmentation breaks a large habitat into smaller, separated patches. The patches behave like islands, so small, isolated fragments lose species over time.
Island species often evolve to use a narrow set of foods or places, because islands offer few resources. They can lose out when people bring species from elsewhere that can live on many foods.

more seeds, insects, birds and other colonists reach it, so new species arrive often it has more habitats and larger populations, so fewer of its species die out large, near islands settle at the most species; small, far islands at the fewest each patch acts like an island, and the smallest, most isolated patches lose the most species

island biogeography: The study of how many species live on islands and why. Larger islands and islands closer to a source of colonists hold more species. The ideas also apply to habitat islands such as lakes, mountaintops and forest fragments.
habitat fragmentation: The breaking of a large, continuous habitat into smaller patches separated by roads, farms, towns or other land its species cannot use. The patches act like islands, and small, isolated patches tend to lose species.

2.4 Ecological Tolerance

Every species has a range of tolerance for each abiotic factor. In the optimal range individuals thrive and populations are largest; in the zones of physiological stress they survive but grow and reproduce poorly; beyond the limits, in the zones of intolerance, they die. Where conditions move out of a species’ range, its population shrinks, moves or disappears.

Each species has a range of tolerance for each abiotic factor (temperature, salinity, light, water): the conditions it can survive in.
Inside the range, the optimal range is where individuals grow and reproduce best, and the population is largest.
Toward the edges are zones of physiological stress: individuals survive but feed, grow or reproduce poorly, so the population is small. Beyond the limits lie zones of intolerance, where none survive.
Tolerance applies to individuals and to whole populations. Individuals in a population vary, so some tolerate a little more than others.

individuals enter a zone of physiological stress: they grow, feed or reproduce less fewer individuals survive and reproduce, so the population shrinks individuals die (the zone of intolerance), and the population disappears from that place or moves

range of tolerance: The range of values of an abiotic factor, such as temperature or salinity, that an organism or population can survive. Also called ecological tolerance. Each species has a range for each factor.
optimal range: The part of a range of tolerance where individuals of a species grow, feed and reproduce best, so its population is largest.
zone of physiological stress: The parts of a range of tolerance between the optimal range and the limits, where individuals survive but grow, feed or reproduce poorly. Beyond these zones lie the zones of intolerance, where individuals die.

2.5 Natural Disruptions to Ecosystems

Natural disruptions such as floods, droughts, fires, storms and eruptions change ecosystems for a short or a long time. They can be periodic (regular), episodic (recurring at irregular intervals) or random. Over geological time, Earth’s climate and sea level have changed many times. Organisms respond by surviving in place, migrating to suitable places, or dying out locally.

A natural disruption is a natural event that changes an ecosystem: a flood, drought, wildfire, hurricane, volcanic eruption, earthquake or a long shift in climate.
Disruptions differ in timing. Periodic ones come at regular intervals (spring floods, a dry season). Episodic ones recur, but at irregular intervals (droughts, many wildfires). Random ones have no pattern (an eruption, an earthquake).
Disruptions can be short-term (a storm) or long-term (a climate that warms over thousands of years). Earth’s climate and sea level have changed many times; sea level was about 120 meters lower than today about 20,000 years ago, when more water was locked in glaciers on land.
Organisms often respond by migrating: moving, for a season or for good, to places where conditions suit them.

it kills organisms, removes habitat or changes abiotic conditions such as water, temperature or light those populations shrink, die out locally or migrate to places that still suit them the ecosystem recovers, or is replaced by a different community if the change is large or lasting

natural disruption: A natural event that changes an ecosystem, such as a flood, drought, wildfire, hurricane, volcanic eruption or a long-term change in climate. Disruptions can be periodic (regular), episodic (recurring at irregular intervals) or random (no pattern), and short-term or long-term. Also called a disturbance.

2.6 Adaptations

Populations respond to environmental change through natural selection. Individuals differ in heritable traits; those whose traits suit the environment survive and reproduce more, so those traits become more common over generations, and the population becomes adapted. Individuals do not adapt within their lifetime, and populations with little genetic variety, or facing very fast change, may not adapt in time.

Natural selection: individuals with heritable traits that suit their environment survive and reproduce more, so those traits become more common in the population over generations.
An adaptation is a heritable trait that helps an organism survive and reproduce in its environment, such as a deep beak for cracking hard seeds or thick fur in a cold climate.
Natural selection acts on populations over generations. An individual does not adapt during its life; the population shifts because some individuals leave more offspring.
Populations need genetic variety to adapt. When the environment changes faster than a population can adapt, the population may decline or die out.

some individuals are better suited than others to the current environment individuals with suited traits (deep beaks) survive and reproduce more than others the suited trait becomes more common in the next generation the population becomes adapted to its environment; if change is too fast, it may die out instead

natural selection: The process by which individuals with heritable traits that suit their environment survive and reproduce more than others, so those traits become more common in the population over generations.
adaptation: A heritable trait that helps an organism survive and reproduce in its environment, such as thick fur in a cold climate. Adaptations become common in a population through natural selection over many generations, not within one organism’s lifetime.

2.7 Ecological Succession

Ecological succession is the series of changes in a community after a disruption. Primary succession begins on bare rock with no soil, and pioneer species such as lichens and mosses help form soil; it is slow. Secondary succession begins where soil remains, after a fire, flood or abandoned farm; it is faster. Over the stages, biodiversity and biomass increase until a mature, more stable climax community develops.

Ecological succession is the gradual change in the species of a community after a disruption, in a series of stages.
Primary succession starts where there is no soil: new lava rock, rock left by a retreating glacier. Soil must form first, so it is slow (often centuries).
Secondary succession starts where soil remains after a disruption such as a fire, a flood, a hurricane or an abandoned farm field. With soil and seeds already present, it is faster (often decades).
Pioneer species (lichens and mosses on rock; grasses and weeds on soil) arrive first. Over time biodiversity and biomass increase, and a mature, more stable climax community develops.

pioneer species, which grow fast and spread easily, arrive first conditions become suitable for larger plants that could not grow there before the community changes in stages, and species richness and biomass increase a mature, more stable community (climax community) develops

ecological succession: The gradual change in the species that make up a community after a disruption, in a series of stages that usually leads toward a mature, more stable community.
primary succession: Succession that starts where there is no soil, such as new lava rock or rock exposed by a retreating glacier. Pioneer species such as lichens and mosses help form soil, so it is slow, often taking centuries.
secondary succession: Succession that starts where soil remains after a disruption such as a fire, flood, hurricane or abandoned farm field. Because soil, seeds and roots remain, it is faster than primary succession, often taking decades.
pioneer species: The first species to colonize a disrupted area: lichens and mosses on bare rock, or grasses and weeds on bare soil. They grow fast, spread easily and change conditions so that other species can follow.
climax community: The mature, relatively stable community that develops at the end of succession if there is no major disruption for a long time, such as an old forest. Also called a mature community.