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Population & Community Ecology

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Presentation on theme: "Population & Community Ecology"— Presentation transcript:

1 Population & Community Ecology
Chapter 35

2 35.1 A population is a local group of organisms of one species
I. Defining Populations A. A populations size is determined by the availability of food and space, weather conditions, and breeding patterns B. When scientists study populations they must determine its boundaries, such a lake, a state or the whole country

3 Boundaries Regional Local

4 What is a species? Distinct form of life
Population of organisms which can breed and produce offspring

5 Peacock + Peahen = Peachicks
What about these? Peacock + Peahen = Peachicks Horse + Donkey = Mule

6 II. Population Density A. Population Density is the number of individuals of a particular species per unit of area or volume B.Population density is useful when comparing two populations in different areas Class Example.

7 III. Sampling Techniques
A. Since it is impossible to count every member of a population scientists use sampling techniques to estimate the size of a population Quadrats- scientists mark off a square boundary at several locations and take an average (plants) Indirect Counting- counting nests, burrows or tracks instead of the organisms themselves (insects) 3. Mark-Recapture- scientists trap and mark individuals (birds) B. Most sampling techniques involve making assumptions about the populations being studied

8 Which sampling technique?
Bats: mark-recapture Black bear: indirect Cactus: quadrat

9 Population Distribution

10 Which distribution pattern?
Termite Mound Rattlesnake Random Clumped

11 35.2 Limits to population growth
I. Exponential Growth of Populations A. A population’s ability to grow partly depends on the rate at which its organisms can reproduce B. Exponential Growth is when the population multiplies at a constant factor at constant time intervals i.e. bacteria doubling every 20 minutes

12 Transparency 35A-1

13 Transparency 35A-2

14 Transparency 35A-3

15 Transparency 35A-4

16 Transparency 35A-5 1. Compare and contrast the two growth curves.
Both curves show a period of rapid population growth, but the fur seal population eventually levels off. The bacterial population appears to continue growing exponentially.

17 Transparency 35A-6 2. Which curve do you think more closely resembles the growth of most populations in nature? Explain. Limited growth curve; populations in nature are subject to limiting factors that prevent long-term exponential growth.

18 II. Carrying Capacity A population may start to grow exponentially, but eventually one or more environmental factors will limit its growth B. A limiting factor is a condition that can restrict a population’s growth C. The carrying capacity is the number of organisms in a population that the environment can maintain or “carry”

19 III. Factors Affecting Population Growth
Density-Dependent Factors is a factor that limits a population more as a population density increases B. Density-Independent Factors are factors that limit population but are unrelated to population density

20 Temperature and humidity
Population Growth Temperature and humidity Food availability Density- Independent Density-dependent

21 IV. Population Cycling A “boom” and “bust” growth cycle is one that increases rapidly followed by a sharp decline B. Other growth cycles are influenced by those of other populations in their environments

22 Population Cycling

23 35.3 Predicting the impact of human population growth


25 Population (Millions)
10 Largest Countries Country Population (Millions) 1. China 1,311 2. India 1,122 3. United States 299 4. Indonesia 225 5. Brazil 187

26 Population (Millions)
10 Largest Countries Country Population (Millions) 6. Pakistan 166 7. Bangladesh 147 8. Russia 142 9. Nigeria 135 10. Japan 128

27 Population (Millions)
10 Largest Countries Country Population (Millions) 1. India 1,628 2. China 1,437 3. United States 420 4. Nigeria 299 5. Pakistan 295

28 Population (Millions)
10 Largest Countries Country Population (Millions) 6. Indonesia 166 7. Brazil 147 8. Bangladesh 142 9. Rep. of Congo 135 10. Ethiopia 128

29 History of Human Population

30 History of Human Population

31 Human Pop Graph

32 I. History of Global Population Growth
For most of human history, the human population has grown very slowly or not at all B. Human population growth depends on birth rates and death rates C. The introduction of farming has provided a stable food supply so birth rates have gone up D. Advances in modern medicine, nutrition and sanitation have caused death rates to go down E. These factors have caused the human population to increase dramatically

33 Transparency 35B-1

34 Transparency 35B-2 1. Which age group forms the largest bulge in the age-structure graph of the United States? Of Kenya? 40–44; under 5

35 Transparency 35B-3 2. Which country is likely to undergo the greatest increase in population in the next 20 years? Explain. Kenya; the majority of the population is under 25 years old, which is the portion likely to have children in the next 20 years.

36 II. Predicting Future Population Growth
The Age Structure of a population is the proportion of people in different age groups B. Prediction of future growth varies because of the difficulty predicting future birth and death rates of various countries C. The question remains whether or not Earth will have the capacity for the human population

37 35.4 Species interact in biological communities

38 I. Competition Between Species
Members of a population may compete for the same limited resource B. Within a community, interspecific competition takes place when two or more species rely on the same limited resource C. If two species are so similar in their requirements that the same resource limits both species’ growth it is called competitive exclusion D. A niche includes an organisms living place, its food source, the time of day it is most active and many other factors that are specific to that organism’s way of life

39 Competitive Exclusion

40 II. Predation Predation is when one organism eats another
B. Eating and avoiding being eaten are important to survival and predators and prey have developed many adaptations Predator adaptations include: being fast and agile, coloring that camouflages, hunting in groups, acute sense to find prey and having claws, teeth, fangs and stingers to help catch prey 2. Prey adaptations include: retreating or fleeing from predators, camouflage, defensive coloring, mimicry, secreting poisonous chemicals, having spines and thorns

41 Predator-Prey Relations

42 III. Symbiotic relationships
A symbiotic relationship is when two species live in or on one another B. There are three main types of symbiotic relationships Parasitism- A parasite gets it’s food at the expense of another organism, i.e. mosquitos and humans 2. Mutualsim- Both organism benefit from the relationship, i.e. E.Coli and humans 3. Commensalism- One organism benefits and the other is neither hurt nor helped, i.e. sharks and remoras

43 Symbiosis Parasitism Win + Lose - Mutualism Commensalism Tie

44 Symbiosis - Which is it? Predator-Prey Parasitism Mongoose & Cobra
Liver Fluke

45 Symbiosis - Which is it? Commensalism Mutualism Clownfish & Anemone
Air Plant

46 35.5 Disturbances in communities
I. Disturbances to Communities A. Natural Disturbances are events such as fires, volcanic eruptions, floods, storms, and droughts all destroy resources such as shelter and water B. Disturbances can be either positive or negative C. Humans also have an impact on communities which can be either positive or negative

47 Surviving Environmental Change

48 II. Ecological Succession
The series of changes in the species in a community, often following a disturbance is known as ecological succession There are two types of succession: Primary succession which is when new community arises from a previously lifeless area i.e. plants growing on a volcanic island 2. Secondary succession is when a new community arises from a previous community i.e. a forested area which has been cleared and abandoned

49 Primary Succession

50 Secondary Succession

51 III. Human activities and species diversity
60% of the Earth’s land is used by humans, mainly for cropland or rangeland Humans usually have a negative effect on species in two ways Clearing the Land- Humans clear vast amounts of land to make way for farming and building 2. Introduced Species are species that are moved from one location to another either accidentally or on purpose. These new species may take over an area and prey on native species or drive them from their niches

52 Invasive species in Washington

53 Invasive species in Ohio
Canada thistle Dutch Elm disease Emerald ash borer Zebra mussel


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