Populations

in an Ecosystem

Biology

Standards: SC.912.N.1.4, SC.912.L.17.4, SC.912.L.17.5, SC.912.L.17.8

Textbook: Chapter 5.1 thru 5.3

Populations

A. Limiting Factors (17.5)

1. Density-Dependent

a. Predation

b. Competition

c. Human Activity

2. Density-Independent (17.4, 17.8)

a. Seasonal Variations

b. Natural Disasters & Catastrophic Events

B. Population Dynamics and Graphs (17.5)

1. Type of Growth

a. Exponential growth

b. Logistic growth

2. Carrying Capacity (17.5)

3. Factors Affecting Population Growth

a. Birth rates and death rates

b. Immigration and emigration

c. Predator-prey relationships

OBJECTIVES

A. Describe and investigate various limiting factors in the local ecosystem and their impact on native populations, including food, shelter, water, space, disease, parasitism, and predation.

B. Analyze data and information about population dynamics and limiting factors to explain a change in carrying capacity, the effect of population size, or the distribution of species in various types of ecosystems.

Vocabulary:

organism, population, limiting factor, density dependent, density independent, mortality (death rate), natality (birth rate), emigration, immigration, carrying capacity, competition, predator, prey, exponential growth, logistic growth

Powerpoint: Chapter 5 Populations

How Populations Grow

Geographic Range – the area a population lives

Population Density – the number of individuals in an area. A member of a low-density population—where organisms are sparsely spread out—might have more trouble finding a mate to reproduce with than an individual in a high-density population.

A member of a low-density population—where organisms are sparsely spread out—might have more trouble finding a mate to reproduce with than an individual in a high-density population.
Population Growth
Number of births
Number of deaths
Emigration (exit or leave population) & Immigration (come IN the population)

Positive Growth rate = population increase > 0

Negative Growth rate = decrease < 0

Stable population= 1 (no increase or decrease)

Exponential Growth –reproduce at a constant rate. Occurs under ideal conditions (no limits)

J-shape curve

Logistic Growth – resources become less available, growth slows or stops

S-shape curve

Carrying Capacity – the number an environment can support

In exponential growth, a population's per capita (per individual) growth rate stays the same regardless of population size, making the population grow faster and faster as it gets larger.
In nature, populations may grow exponentially for some period, but they will ultimately be limited by resource availability.
In logistic growth, a population's per capita growth rate gets smaller and smaller as population size approaches a maximum imposed by limited resources in the environment, known as the carrying capacity.

Population Distribution

The individual organisms that make up a population can be more or less equally spaced, dispersed randomly with no predictable pattern, or clustered in groups. These are known as uniform, random, and clumped dispersion patterns, respectively.

The organisms in a population may be distributed in a uniform, random, or clumped pattern. Uniform means that the population is evenly spaced, random indicates random spacing, and clumped means that the population is distributed in clusters.
- - - - Larger populations may be more stable than smaller populations because they’re likely to have greater genetic variability and thus more potential to adapt to changes in the environment through natural selection.

Uniform In uniform dispersion, individuals of a population are spaced more or less evenly. One example of uniform dispersion comes from plants that secrete toxins to inhibit growth of nearby individuals—a phenomenon called allelopathy. We can also find uniform dispersion in animal species where individuals stake out and defend territories.
Random dispersion. In random dispersion, individuals are distributed randomly, without a predictable pattern. An example of random dispersion comes from dandelions and other plants that have wind-dispersed seeds. The seeds spread widely and sprout where they happen to fall, as long as the environment is favorable—has enough soil, water, nutrients, and light.
Clumped dispersion. In a clumped dispersion, individuals are clustered in groups. A clumped dispersion may be seen in plants that drop their seeds straight to the ground—such as oak trees—or animals that live in groups—schools of fish or herds of elephants. Clumped dispersions also happen in habitats that are patchy, with only some patches suitable to live in.

Limiting Factors

Limiting Factors – causes population growth to decrease

Density-dependent limiting factors cause a population's per capita growth rate to change—typically, to drop—with increasing population density; depends on population size. One example is competition for limited food among members of a population.
- - Examples: competition, predation, parasitism and disease
Density-independent factors affect per capita growth rate independent of population density. Examples include natural disasters like forest fires. Does not depend on population size.

- Examples: Unusual weather, Natural disasters, Some human activities

Limiting factors of different kinds can interact in complex ways to produce various patterns of population growth

Demography: The study of human populations

As countries became more developed, food supplies

became more reliable, and the global human population began to grow more rapidly. That trend

continued through the Industrial Revolution in the 1800s. In addition to improved nutrition,

improvements in sanitation, medicine, and public health dramatically reduced death rates. Yet

birthrates in much of the world remained high. The combination of lower death rates and high

birthrates led to exponential growth.

Demography- study of human populations

Demographic Transition – a dramatic change in high birth and death rates to low birth and death rates

Age Structure Diagrams can be used to evaluate populations. Demographers consider many factors to predict human population growth. The factors include age structure, the effects of deadly diseases such as AIDS, malnutrition, and death rates. Currently projections suggest that by 2050 the world population will reach 9 billion people.

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