Represents amount of energy available at each level as well as amount of living tissue—both decrease with each increasing trophic level

Energy and Biomass Pyramid (together)

V. Ecological Interactions between organisms

A. Competition—when two organisms of the same or different species attempt to use an ecological resource in the same place at the same time.

Ex: food, water, shelter

Monkeys compete with each other and other animals for food.

Rams compete with each other for mates.

Until Americans introduced gray squirrels into parts of England in the early 20th century, red squirrels had been the only species of squirrel in the country. The gray squirrels were larger and bred faster and successfully competed for resources. Within a couple years of overlap in an area, the red squirrels disappeared.

B. Niche—the ecological niche involves both the place where an organism lives and the roles that an organism has in its habitat.

Example: The ecological niche of a sunflower growing in the backyard includes absorbing light, water and nutrients (for photosynthesis), providing shelter and food for other organisms (e.g. bees, ants, etc.), and giving off oxygen into the atmosphere.

The ecological niche of an organism depends not only on where it lives but also on what it does. By analogy, it may be said that the habitat is the organism’s “address”, and the niche is its “profession”, biologically speaking.

Worm’s Niche“Address”—Soil, Ground, etc.

“Profession”– Mix-up soil

C. Predation—one organism captures and feeds on another organism

1. Predator—one that does the killing

2. Prey—one that is the food

D. Symbiosis—any relationship in which two species live closely together

1. Mutualism—both species benefit (WIN-WIN)a. Ex: insects and flowers

Can you think of any other examples that we’ve talked about in class?

2. Commensalism—one member of the association benefits and the other is neither helped nor harmed.(WIN-0)

Example: barnacles on a whale

Commensalism

The Remora fish attaches to the shark and gets a free ride.

Birds build nests in trees.

3. Parasitism—one organisms lives on or inside another organism (host) and harms it.The parasite obtains all or part of its nutritional needs from the host. (WIN-LOSE)

Example: fleas on a dog

Parasitism

Wasp eggs on back of caterpillar.

Mosquito biting a human.

Sea lampreys feed on fluids of other fish.

Mutualism, Commensalism or Parasitism??

Parasitism

Mutualism

Ecological Levels

Density and Distribution of Populations

• Population Density - Number of individuals per unit area or volume.

• Population Distribution - Pattern of dispersal of individuals within the area of interest.

Uniform Distribution

Random Distribution

Clumped Distribution

Characteristics of Populations• They tend to grow• Intrinsic Rate of Natural Increase

(r)

Population Growth Models

• Exponential Growth• Biotic Potential • Environmental Resistance

Exponential Growth Curve

Logistic Growth

• Logistic growth—indicated by an S-shaped curve

• Difference between logistic and exponential due to environmental resistance

Logistic Growth

Carrying Capacity

• Carrying Capacity is the maximum number of individuals of a given species the environment can support.– The closer the population to the carrying capacity,

the greater the environmental resistance.• Biotic potential is having full effect and birthrate is a

maximum during exponential growth.

St. Paul Island Reindeer Population

Mortality Patterns• Cohort --- all the members of a population

born at the same time.• Survivorship---the probability of newborn

individuals of a cohort surviving to particular ages.

• Illustrated by Survivorship Curves

Survivorship Curves

Survivorship Curves

Age Distributions• What proportion of population

is in each cohort? • Age Structure Diagrams

U.S. Age Distributions

Regulation of Population Size• Density - Dependent Factors• Density - Independent Factors

Factors That Affect Population Size

Density Dependent Factors

1. Competition Intraspecific Interspecific

2. Predation

3. Parasitism

4. Disease

Factors That Affect Population Size

Density Independent Factors

1. Abiotic factors

2. Unpredictable, catastrophic

events

Life History Patterns• r - Strategists (Opportunistic)• Remember r=reproduction

Life History Patterns• k - Strategists (Equilibrium)

• Remember k=Karrying kapacity

Human Population Growth

• Human population has had an exponential growth pattern.– Doubling time currently estimated at 53 years.

• Population Size– 1800 1 Billion– 1930 2 Billion– 1960 3 Billion– 2000 6 Billion

World Population Growth

Country Development• More-Developed Countries (MDCs)

GR=0.1%• Less-Developed Countries (LDCs)

GR= 1.6%– LDC population expected to

increase from 5-8b by 2050

Age Distributions

• Age Structure Diagrams divide populations into three age groups.–Pre-Reproductive–Reproductive–Post-Reproductive

The Demographic Transition• Stage I: high birthrates and death rates• Stage II: continued high birthrates, declining

death rates• Stage III: falling birthrates and death rates,

eventually stabilizing

More-Developed Countries

Less-Developed Countries

Population Structures by Age and Sex, 2005 Millions

300 100 100 300300 200 100 0 100 200 300

Less Developed Regions

More Developed Regions

Male Female Male Female

80+ 75-79 70-74 65-69 60-64 55-59 50-54 45-49 40-44 35-39 30-34 25-29 20-24 17-19 10-16

5-90-4

Age

Source: United Nations, World Population Prospects: The 2002 Revision (medium scenario), 2003.

Age Distribution of the World’s Population

World Population Distribution by Region, 1998 and 2050

Environmental Impact

• Measured in terms of:–Population Size–Resource Consumption Per

Capita –Resultant Pollution

Environmental Impact

Review• Scope of Ecology• Population Density and Distribution• Population Growth Models• Survivorship Curves• Age Distributions• Regulation of Population Size• Life History Patterns• Human Population Growth

– Environmental Impact

• facstaff.bloomu.edu/.../Ecology%20of%20Populations%20online%20