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**Understanding populations**

ECOLOGY Understanding populations

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**Features that determine the future of a population:**

Population size- the # of individuals in a population Population density- the # of individuals in a given area Dispersion-the way individuals are arranged in space

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How many populations?

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**How many different populations can you see?**

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What is a population? A population refers to all the members of one species, in one place at one time.

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DISPERSION: How members of a population are arranged in a given space.

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**Patterns of dispersion**

Individuals in a population may be distributed according to 3 basic patterns of dispersion Random Uniform (also known as Even) Clumped

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**Random Dispersion Scattered, not uniform Why? Environment is uniform**

Individuals are solitary They live independently Pine trees in a random distribution

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**Birds in an even distribution**

Uniform Dispersion About equal distance apart, forming a pattern Why? Resource competition Birds in an even distribution

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**Buffalo in a clumped distribution**

Clumped Dispersion Grouped in some places, absent in others irregular pattern Why? Resources are patchy Search for food Buffalo in a clumped distribution

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**Why do you think scientists study population dispersion?**

How individuals are arranged within a population can affect... Protection (from predators) Hunting patterns (if carnivorous) Reproduction

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**Can you name the 3 patterns of dispersion?**

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Clumped Uniform Random

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Population density: The number of individuals in a population that live within a given area.

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Population Density Scientists study the population density because it helps determine how the individuals of a population interact. Reproduction Protection Eating patterns Social hierarchies, if any

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**Which population of wildebeest has the greatest population density?**

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**An extremely dense population of wildebeest:**

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**Modeling Population growth**

Population success = reproduction of species We can study how and why the number of individuals change over time Populations grow when more individuals are born than die in a given period. A simple population model describes the growth rate as shown: (r) = birthrate – death rate

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**Describe what is happening to the population in this graph**

AGE # of Individuals A small # of the youngest-decrease Middle age population is constant, secure, not changing The older population decreases, faster

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Exponential Growth Exponential growth-the rate of population growth stays the same and the population size increases steadily. This model displays a J-shaped curve which indicates a steady increase of population size.

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**What if the population size kept growing and growing and...**

carrying capacity (K)- the population size that an environment can sustain What factors do you think contribute to an environment's carrying capacity???

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Factors that can affect a population

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Density-dependent factors Resources that are limited because the rate at which they become depleted depends on the density of the population that uses them.

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Density-dependent factors Shelter Food Water

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LOGISTIC GROWTH MODEL Once again, exponential growth is a steady increase in the population size. Now we must consider the carrying capacity (K) and density-dependent factors when modeling population growth. logistic model- a population model in which exponential growth is limited by a density-dependent factor. This model considers carrying capacity.

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LOGISTIC MODEL

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Density-independent factors Factors that do not depend on the size of the population, but can affect it nonetheless.

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Density-independent factors Weather Climate

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Remember... (r)= rate of growth, birthrate – death rate (K)= carrying capacity, the population size an environment can sustain There are 2 types of populations, (r)-strategists and (K)-strategists

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r-strategist: Species that grow exponentially when the environment allows for it. Results in temporarily large populations. When the environmental conditions are no longer suitable for the species, the population size quickly decreases.

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**K- strategists- organisms that grow slowly**

K- strategists- organisms that grow slowly. Population sizes are usually small and kept near the carrying capacity of their environment. K-strategists are characterized by a long life span, a slow maturing process, and reproduction late in life.

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