Chapters 3-5

Communities,

Population Biology, Biological Diversity & Conservation

Living in the Community

n    Community – collection of interacting populations

n    Limiting Factors – environmental factors that affect an organism’s ability to survive in its environment

–   Can be living: food availability, predators

–   Can be non-living: temperature, water, sunlight

–   Can  affect a population directly or indirectly

•    For instance, food availability will affect a herbivore and the carnivore that eats the herbivore

Ranges of Tolerance

n    Tolerance – the ability of an organism to withstand fluctuations in biotic and abiotic environmental factors

–   Each organism has a specific range that it can survive in for a specific factor

–   Ex: catfish can tolerate warm water with little oxygen, while  bass or trout cannot

 

Succession

n    Let’s say you no longer cut your lawn.  What would happen with sufficient water?

1. The grass gets taller; weeds start to grow.  The area resembles a meadow.

2. Later, bushes grow, trees appear and different animals enter the area to live.

3. The bushes and trees change the environment; less light reaches the ground. The grass slowly disappears.

4. Thirty years later, the area is a forest.

Succession

n      The orderly, natural changes and species replacements that take place in the communities of an ecosystem

n      Primary Succession – the colonization of new sites by communities of organisms

n      Pioneer Species – the first species in an area

–    Ex: Lichen (a combination of fungus and algae) grows readily after a volcanic eruption

–    Lichens break up rock slowly and help soil accumulate

–    Slowly, more things are able to live in the environment

n      Climax Community – mature community that undergoes little or no change

–    Ex: Deciduous forest

 

Secondary Succession

n     The sequence of community changes that takes place after a community is disrupted by natural disasters or human actions

–    Occurs on land that already has soil

–    The pioneer species will be different and the community will climax in a shorter time

n     Example:  Yellowstone burned in 1988

–    Wildflowers came back first, then grasses, ferns and pine seedlings

Biome

n     A biome is a large group of ecosystems that share the same type of climax community

n     There are terrestrial biomes (tundra, taiga, desert, grassland, temperate forest, rain forest, etc.)

n     There are aquatic biomes (marine, estuaries, freshwater)

 

Chapter 4 – Population Biology

n      Population Growth – an increase in the size of a population over time

n      All populations start off growing relatively slowly (relative to their capacity to reproduce)

n      If resources are not limited, all populations will grow exponentially (a “J” curve)

–    E. coli reproduce every 20 minutes and could produce a colony equal to the size & weight of the Earth in one day

Realistic Population Growth

n    Resources are never unlimited

n    Populations will reach a carrying capacity – the number of organisms of one species that an environment can support

n    Populations follow an S-shaped growth curve

Patterns of Population Growth

n     Some organisms reach their carrying capacity faster than others

–    This is due to their reproductive patterns

n     Environmental Conditions

–    Ideal ranges

n     In general, organisms that are small and mature rapidly reach carrying capacity faster

–    Organisms that are large and mature slowly, reach a carrying capacity slower

Environmental Limits to
Population Growth

n     Density-Dependent Limiting Factors have an increasing effect as the population increases

–    Ex: disease, competition, parasites, food

–    Ex: How does predation effect population sizes?

n     Density-Independent Limiting Factors affect all populations, regardless of their density

–    Most are abiotic factors such as temperature, storms, flood, drought, habitat destruction

Density-Dependent Limiting Factors

n    Competition – increases within species as population gets too big. 

–  Over food, water, territory, mates, etc.

–  Can you see this in a human population?

Density-Dependent Limiting Factors

n     Crowding & Stress – as populations increase in size, individual animals begin to exhibit:

–    Aggression

–    Decrease in parental care

–    Decreased fertility

–    Decreased resistance to disease

–    Can you see this in a human population?

 

Demographic Trends

n    Demography – the study of human population growth characteristics

–   i.e., growth rate, age structure, geographic distribution

n    Humans reduce negative environmental effects on our population

–   i.e., eliminating competitors, increasing food production, controlling diseases

n    Human Population (see pg. 100 in book)

–   1 A.D. – around 1850 : slow growth

–   After 1850-present: exponential growth (J-curve)

 

Realistic Population Growth

n    Where are humans on this curve?

n    What will eventually have to happen? 

Birth and Death Rates

n     Death Rate – the number of deaths per 1000 people in a given year

–    Affected by life expectancy, diseases in area, stress, etc.

–    Difference in Africa and U.S.?

n     Birth Rate – the number of live births per 1000 people people in a given year.

–    Fertility rate is a large influence here

–    Difference in Africa and U.S.?

Population Growth Rate (PGR)

n    Immigration – movement of individuals into a population

n    Emigration – movement from a population

n    Population Growth Rate = (Birthrate + Immigration Rate) - (Death Rate + Emigration Rate)

n    Or, for convenience

–   PGR = Birthrate - Death rate

n    When birthrate equals death rate, the population isn’t growing

n    As long as the PGR is positive, the population will continue to grow

 

Doubling Time & Age Structure

n     Doubling Time - the time needed for a population to double in size

–    Doubling Time (in years) = 70/annual percent growth rate

–    What is happening to the world doubling time?

n     Age structure refers to the proportions of a population that are at different age levels

–    If a population has many young members, it will mostly likely grow rapidly

–    If a population has equal numbers of ages, it is stable

–    Look page 103 in book

n     These demographics do not influence world population, but do show movement from or to urban areas, countries, etc.

 

Ecology and Growth

n     Population needs differ throughout the world

n     Some populations have competition for food, water, etc.

n     Some population are more concerned about the health of their citizens

n     When populations grow rapidly, there is often competition for resources

–    Lead to stress, contamination, etc. that lead to disease and affect stability of populations

 

Biological Diversity

n     Biodiversity refers to the variety of life in an area

–   Most common measure is the number of species that live in a certain area

n     Terrestrial biodiversity tends to increase as you move towards the equator (or in isolated warm regions)

–   2/3 of all land species on Earth are in tropical regions

n     The size of the area also affects biodiversity

–   Larger areas tend to be more diverse (unless other things prevent or encourage life)

Importance of Biodiversity

n    Organisms are adapted to live together in a community

–   If you take one away, there are consequences to the rest

n    Biodiversity brings stability to an ecosystem

–   More resources, interactions, etc.

–   When a population utilizes more than one resource, it will be ok if one of them disappear

n    Biodiversity is important to humans

_–     Oxygen to breath, remove CO₂

–   Diverse diet / Better crops                   (resistance)

–   Building materials

–   Possible pharmaceuticals

 

Loss of Biodiversity

n      Extinction – the disappearance of a species when the last of its members dies

–    Since 1980, almost 40 species of plants and animals have gone extinct in the U.S.

–    Can be natural or human-caused

–    Passenger pigeon

n      Threatened Species – when the population of a species begins declining rapidly

–    In the US:  sea otters, loggerhead turtles, bald eagle

n      Endangered Species – population numbers so low that extinction is possible

–    In the US: California Condor, Florida manatees

Threats to Biodiversity

n     Habitat loss – the biggest threat

–   Take away resources for life

n     Habitat fragmentation – separation of wilderness areas from other wilderness areas

–   Roads – leads to less biodiversity

–   Animals that migrate or need large areas to hunt

–   Climates can change (take away shade)

–   Edge Effect – the different conditions along the boundaries of an ecosystem

Threats to Biodiversity

n     Habitat Degradation – the damage to a habitat by pollution

–    Air, Water, or Land

n    Air Pollution

n     Burning fossil fuels is the greatest source of air pollution

n     Acid Precipitation – sulfur dioxide from burning coal and nitrogen oxides from automobile exhausts                           combine with water vapor

–    Leaches nutrients from the soil

–    Damages plant tissues

–    Alters pH of lakes

_n       Ozone layer damage – CFC’s break down 0₃

–    Increased skin cancers

–    Possible cause for amphibian population decreasing

Threats to Biodiversity

n    Water Pollution

n     Fertilizers and animal wastes carried by runoff

–    Causes algal blooms

–    These algae die, decay and remove oxygen from the water

n     Silt from erosion clogs gills, blocks sunlight

n     Detergents, metals, industrial chemicals from runoff

n     Debris in oceans and lakes

Threats to Biodiversity

n   Land pollution

n    Trash – the average American produces about 1.8 kg of solid waste daily – 657 kg/yr

–  Destroy habitats and pollute areas

n    Pesticides, etc. can also lead to habitat degredation

–  DDT

Threats to Biodiversity

n    Introduction of Exotics

n     Exotic species – organisms that are not native to a particular area

–   Can grow at an exponential rate due to a lack of competitors and a lack of predators

–   Take over niches of native                    species or replace the                           species

•    Sea lamprey in Great                          Lakes after Erie Canal

•    Goats on Santa Catalina                     Island

 

Conservation Biology

n    Conservation Biology is the study and implementation of methods to protect biodiversity. 

–   Natural resource conservation - natural resources are those parts                    of the environment that                    are useful or necessary                      for living organisms. 

–   Species conservation -             protecting species from             extinction and preserving biodiversity

Legal Protection of Species

n    1973, the U.S. Endangered Species Act made it illegal to harm any species on the endangered or threatened list

•    Illegal for federal agencies to                                                       fund any project that would                                                         harm these species

 

 

n    The Convention on International Trade in Endangered Species (CITES)

–   Established lists of species for which international trade is prohibited or controlled

–   Honored by 120 countries

Preserving Habitats

n    One way is to create national parks

–  First one in US was Yellowstone

–  Originally this was to preserve the geology

n    Protects natural                 environments and                provides habitats                          for many organisms

n    What are other ways we preserve land?

Habitat Corridors

n    Protected strips of land that allow the migration of organisms from one wilderness to another

–   Isolated populations inbreed too much

 

Sustainable Use

n    In National Parks, the land is managed

n    This philosophy strives to enable people to use natural resources in ways that will benefit them and maintain the ecosystem

–  Some grazing

–  Harvest fruits

–  Hiking, camping,                                       etc.

 

Preservation Programs

n      Captive Breeding followed by Reintroduction Programs

–    Release organisms into area where the species once lived

–    Ex: black-footed ferret

–    Ex: brown pelican after DDT

n      Seed banks for threatened and endangered plant species