1. Ecology
PART 3

2. Lesson Objectives
Describe ecological levels of organization in the biosphere.
Distinguish between abiotic and biotic factors.
Define organism, population, community, ecosystem, biome, and biosphere as the term are used in ecology and other ecological concepts.
Identify factors that determine population growth rate.
Compare and contrast exponential and logistic growth.
Define limiting factors and their effect on population dynamics.
Compare and contrast niches and habitats.

3. Introduction
Ecology is the study of interactions of living things with each other and their environments.

4. Levels of Organization
Ecologists study organisms and their environments at different levels of organization:
organism→population→communities→ecosystems→biosphere

5. Box 2
Which type of scientist studies organisms & their ecosystem?

6. Organisms: are individual living things.
This is the lowest level of organization that ecologists study. Biologists study organisms, organ systems, organs, tissues, cells, organelles, and molecules. Chemists study atoms and subatomic particles.

7. Population: organisms of the same species that live in the same area, interact with one another, and produce fertile offspring
Community: consists of populations of different species that live in the same area and interact together.

8. Ecosystem: consists of living things and their environment.
Biome: group of ecosystems that have the same climate and dominant communities.

9. Box 3
What are the five levels of organization?

10. Organisms and the Environment
Organisms: life form consisting of one or more cells; has characteristics of life.
Environment includes both living (biotic) and nonliving things (abiotic).

11. Biotic and Abiotic Factors
Biotic living organisms
Abiotic nonliving or physical factors
Together determine productivity of the ecosystem in which organisms’ live

12. Box 4
Are single celled organisms included in the environment?

13. What Is a Population?
In biology, a population is a group of organisms of the same species that live in the same area. How large a population is and how fast it is growing are often used as measures of its health.

14. Population Growth Rate
Population growth rate (r) is how fast a population changes in size over time. A positive growth rate means a population is increasing. A negative growth rate means it is decreasing. The two main factors affecting population growth are the birth rate (b) and death rate (d).

15. Births and Deaths: Balancing Costs of Reproduction and Survival
growth rate = birth rate – death rate
r = b – d
If birth rate exceeds death rate, r is positive and the population grows. If death rate exceeds birth rate, r is negative and the population declines. And if birth rate and death rate are in equilibrium, growth rate is zero, and the population remains stable. In a stable population, each individual, on the average, produces one offspring which survives long enough to reproduce itself. Mere survival is not success in the game of
life; natural selection requires that survivors reproduce. Species vary in the strategies they use to achieve reproductive success, making trade-offs between the energy and time ‘‘costs” of survival and those of reproduction. Age at first reproduction, frequency of reproduction,
number of offspring, parental care, reproductive lifespan, and offspring death rate are some of the traits which build strategies for successful reproduction.

16. After 5 hours of exponential growth; one bacteria yields…
32,768

17. Box 5
How are basic growth rates calculated?

18. Other Factors Affecting Population Growth Rate
Population growth may also be affected by people coming into the population from somewhere else (immigration, i) or leaving the population for another area (emigration, e). The formula for population growth takes all these factors into account.
r = (b + i) - (d + e)
r = population growth rate; b = birth rate; i = immigration rate; d = death rate; and e = emigration rate

19. Patterns of Population Growth
At first, exponentially then logistically until carrying capacity is reached
No population can maintain exponential growth indefinitely. Inevitably, limiting factors such as reduced food supply or space lower birth rates, increase death rates, or lead to emigration, and lower the population growth rate. 1938, Pierre Verhulst derived a mathematical model of population growth which closely matches the S-curves observed under realistic conditions. In this logistic (S-curve) model, growth rate is proportional to the size of the population but also to the amount of available resources. At higher population densities, limited resources lead to
competition and lower growth rates. Eventually, the growth rate declines to zero and the population becomes stable. The logistic model describes population growth for many populations in nature.

20. Box 6
What factors affect population growth rate other than birth & death rates?

21. Limits to Population Growth
limiting factor is a part of a population’s environment – living or nonliving – which controls the process of population growth. Biologists have identified two major types of limiting factors:
Density-dependent factors
Density-independent factors.
Density-dependent limiting factors depend on population size and include competition, predation, parasitism, and disease. Density-independent limiting factors affect all populations regardless of population size and include unusual weather, natural disasters, seasonal cycles, and certain human activities, such as, damming rivers, and clear-cutting forests.

22. Box 7
What are the major types of limiting factors?

23. What Is a Community?
Communities are made up of populations of different species. A community is the biotic part of an ecosystem. It consists of all the populations of all the species in the same area. It also includes their interactions.

24. What Is an Ecosystem?
An ecosystem is a unit of nature and the focus of study in ecology. It consists of all the biotic and abiotic factors in an area and their interactions. Ecosystems can vary in size. A lake could be considered an ecosystem. So could a dead log on a forest floor. Both the lake and log contain a variety of species that interact with each other and with abiotic factors.

25. Ecosystem Components
Niches
Habitats
Competitive Exclusion Principle

26. The Niche
Niche organism’s occupation (role), where it lives, and way in which organism’s use conditions they exist in
Food it eats
Place in food web
How it gets food
Range of temperatures
needed for survival
When and how it
reproduces
No 2 species share the same niche or habitat, can occupy niches that are similar
Habitat where an organism lives

27. The Habitat
Physical environment to which an organisms has become adapted and survives in.

28. Box 8
What are three components of an ecosystem?

29. What Is the Biosphere?
The biosphere is the global sum of all ecosystems; integrating all living beings and their relationships, including their interactions with the elements of the lithosphere, hydrosphere, and atmosphere.

30. Lesson Summary
Ecology is the study of how living things interact with each other and with their environment. The environment includes abiotic (nonliving) and biotic (living) factors.
• Organisms are dependent upon their environments for energy and matter.
• Population growth rate is how fast a population changes in size over time. It is determined by rates of birth, death, immigration, and emigration.
• Under ideal conditions, populations can grow exponentially. The growth rate increases as the population gets larger. Most populations do not live under ideal conditions and grow logistically instead. Density-dependent factors slow population growth as population size nears the carrying capacity.
• A community is the biotic part of an ecosystem. It consists of all the populations of all the species that live in the same area. It also includes their interactions.
• An ecosystem consists of all the biotic and abiotic factors in an area and their interactions. A niche refers to the role of a species in its ecosystem. A habitat is the physical environment in which a species lives and to which it is adapted. Two different species cannot occupy the same niche in the same place for very long.
• The biosphere is composed of all the ecosystems on Earth.