Changes in Ecosystems: Ecological Succession

What is Ecological Succession? Natural, gradual changes in the types of species that live in an area Can be primary or secondary The gradual replacement of one plant community by another through natural processes over time

Primary Succession Begins in a place without any soil: Sides of volcanoes Landslides Flooding First, lichens that do not need soil to survive grow on rocks Next, mosses grow to hold newly made soil Known as PIONEER SPECIES

Pioneer Species Species that colonize barren habitats Lichens, small plants with brief life cycles Improve conditions for other species who then replace them

Pioneer Species Low, growing moss plants trap moisture and prevent soil erosion Lichens break down rock to form soil.

Primary Succession Soil starts to form as lichens and the forces of weather and erosion help break down rocks into smaller pieces When lichens die, they decompose, adding small amounts of organic matter to the rock to make soil

Primary Succession Simple plants like mosses and ferns can grow in the new soil

Primary Succession The simple plants die, adding more organic material (nutrients to the soil) The soil layer thickens, and grasses, wildflowers, and other plants begin to take over

Primary Succession These plants die, and they add more nutrients to the soil Shrubs and trees can survive now

Primary Succession Insects, small birds, and mammals have begun to move into the area What was once bare rock, now supports a variety of life

Secondary Succession Begins in a place that already has soil and was once the home of living organisms Occurs faster and has different pioneer species than primary succession Example: after forest fires

Climax Community A stable group of plants and animals that is the end result of the succession process Succession does not always move predictably toward a specific climax community; other stable communities may persist Does not always mean big trees Grasses in prairies Cacti in deserts

Population Biology - Warmup What is a population? What are factors that affect the growth of a population?

Population Size Factors that affect: Natality (birth rate) Mortality/Fatality Immigration Emigration

Population Growth Curves Explain what is happening to the populations below:

Carrying Capacity Carrying capacity - the number of people, other living organisms, or crops that a region can support without environmental degradation. Represented by the variable k = carrying capacity

Population Growth Curves Explain what is happening to the populations below:

Biotic Potential = Reproductive Potential Rate at which a population could grow if it had unlimited resources If a population reached its biotic potential it would have exponential growth

The “J” Curve

The “S” Curve This graph shows a typical population growth curve. Under ideal conditions a population would have a growth with a slow start, then a very fast rate of increase and finally the growth slows down and stops.

Logistic Growth or “S” curve Carrying capacity or “steady state” Not a perfectly straight line Carrying capacity Exponential – rapid growth Availability of food and space limit growth Use example of number of students in this classroom Initial slow growth

Environmental Limits on populations Density-dependent factors % of population affected increases as density increases Examples: Disease Food Parasitism Predation Competition Density-independent factors Effect does not change with population size density Temperature Storms Floods Drought Habitat Disruption Results in “Boom or Bust” Growth curve

Boom or Bust Growth Curve Population July December July December Fluctuates around “line K” Density independent or dependent?

Density Dependent Here is a dramatic example of how competition among members of one species for a finite resource — in this case, food — caused a sharp drop in population. The graph shows a population crash; in this case of reindeer on two islands in the Bering Sea.

Density Independent This graph shows the decline in the population of one of Darwin's finches on Daphne Major, a tiny (100-acre) member of the Galapagos Islands. The decline (from 1400 to 200 individuals) occurred because of a severe drought that reduced the quantity of seeds on which this species feeds. The drought ended in 1978, but even with ample food once again available the finch population recovered only slowly.

Organism Interactions Limit Populations Predation Competition Both types Parasitism Crowding/stress

Predator - Prey Growth Curve Fluctuates around “line K” (carrying capacity)

The Human Population

Demography Vocabulary Age Structure Immigration Emigration Birth/Death Rate

Age Structure Pyramids These population pyramids show the baby-boom generation in 1970 and again in 1985 (green ovals). Profound changes (e.g. enrollments in schools and colleges) have occurred — and continue to occur — in U.S. society as this bulge passes into ever-older age brackets.

Biodiversity & Conservation Importance to nature Importance to people Oxygen Diet Medicines

Loss of Diversity Threatened Species Endangered Species Extinction of Species

Threats to Biodiversity Habitat Loss Habitat Fragmentation Biotic Issues Abiotic Issues Habitat Degradation Air Pollution Water Pollution Land Pollution

Exotic Species Example: Page 124 Non-native organisms that “move-in” to a particular area There can be a lack of competitors = exponential growth Can take over the niches of native species

Conservation Sustainable use: Use what you need, but don’t damage the ecosystem Is this a good example of sustainable use?

Conservation Habitat Corridors

Conservation Reintroduction Programs Captivity Breeding Example: The Ginkgo Tree would probably be extinct if it were not for Chinese monks keeping it in captivity around temples

Biological Controls A living organism used to control the population of another undesirable organism

Biological Controls – Examples Advantages Not toxic to environment Pests won’t become immune Won’t get out of control Disadvantages Doesn’t completely control pest population Takes longer