Interactions in

Ecosystems

Chapter 14

AKS Standards11a - investigate the relationships among organisms, populations, communities, ecosystems, and biomes

A Habitat Differs From a Niche

An organism’s habitat can be described as all of the biotic and abiotic factors in the area where an organism lives. These factors include all aspects of the environment,

including grass, trees, watering holes, etc. An organism’s niche is composed of all of the

physical, chemical, and biological factors that a species needs to survive, stay healthy, and reproduce. You can think of a habitat as where an organism lives

and a niche as how it lives within its habitat. A niche includes, but is not limited to: food, abiotic

conditions, behavior.

Habitat v. Niche

Resource Availability Gives Structure to a Community

A species needs resources such as food, water, and shelter to be successful in its habitat.

While many species can share similar habitats, it is impossible for two species to use the same resource in the same way at the same time…this phenomenon is known as competitive exclusion.

This principle states that when two species are competing for the same resources, one species will be better suited to the niche, and the other species will be pushed into another niche.

This means, simply stated, that NO TWO SPECIES CAN OCCUPY THE SAME NICHE WITHIN A SINGLE ENVIRONMENT.

Resource Availability

Competitive Exclusion

How Long Can You Survive in This Habitat?

http://www.classzone.com/cz/books/bio_07/resources/htmls/animated_biology/unit5/bio_ch14_0430_ab_survival.html

Animated Biology

Connecting Concepts

Considering the competitive exclusion principle, why might it be harmful to transport a species, such as a rabbit, to another habitat where it currently does not exist?

If a new species in introduced to an area, it may occupy a similar niche as a native species and be better adapted for the niche or have no natural predators. This could drive the native species into extinction.

Critical Thinking Activity

AKS Standards11a - investigate the relationships among organisms, populations, communities, ecosystems, and biomes

Competition & Predation are Important Interactions in

Ecosystems Competition occurs when two organisms fight for

the same limited resources. There are two types of competition in nature: Interspecific Competition: occurs when two different

species compete for a limited resource. Intraspecific Competition: occurs when two

members of the same species compete for a limited resource.

Predation is the process by which one organism captures and feeds upon another organisms. In nature, many predators have become highly

adapted to hunting and killing their prey, and many prey have become highly adapted at escaping predation.

Competition & Predation

Interspecific Interactions

Symbiosis is a Close Relationship Between Species

Symbiosis is a close ecological relationship between two or more organisms of different species that live in direct contact with one another.

There are three major types of symbiosis: Mutualism Commensalism Parasitism

Types of Symbiosis

Interspecific Interactions

Community Interactionshttp://www.classzone.com/cz/books/bio_07/

resources/htmls/interactive_review/bio_intrev.html

Interactive Review

Complete this interactive review using your virtual

textbook at home. Concept maps are an

excellent way to organize your thoughts and review

material!

AKS Standards11a - investigate the relationships among organisms, populations, communities, ecosystems, and biomes

Calculating Population Density

Population density is a measurement of the number of individuals living in a defined space.

Calculating accurate population density can tell scientists about a species.

When scientists notice changes in population densities over time, they work to determine whether the changes are the result of environmental factors or are simply due to normal variation in the life history of a species.

Population Density

Understanding Geographic Dispersion in Natural Populations

Population dispersion is the way in which individuals of a population are spread in an area or volume.

Population Dispersion

Analyzing Survivorship Curves A survivorship curve is a generalized diagram

shown the number of surviving members over time from a measured set of births.

Survivorship Curves

Life History Strategies are Diverse in Nature

Some species exhibit big-bang reproduction, which means that they reproduce once and die. These organisms are generally referred to as k-selected species.

Other species exhibit repeated reproduction, whereby they produce a large number of offspring repeatedly. These organisms are generally referred to as r-selected species.

Highly variable or unpredictable environments likely favor big-bang reproduction, while dependable environments may favor repeated reproduction.

Reproductive Strategies

Inferring

An organism has ten offspring. Two of these offspring die each year over a five-year period. Is the organism more likely to be a bird or an insect? Justify your response.

The organism is likely a bird because the mortality pattern described is closest to type II. Insects tend to be type III, with many offspring and high mortality in early life stages.

Critical Thinking Activity

AKS Standards11d - assess and explain human activities that influence and modify the environment such as global warming, population growth, pesticide use, and water/power consumption

Events that Change Population Sizes A population will increase or decrease in size

depending on how many individuals are added to it or removed from it.

Changes in a population’s size are determined mainly by three factors: Immigration: the movement of individuals into

a population from another population (increases population size)

Births: increases population size Emigration: the movement of individuals out of

a population and into another population (decreases population size)

Deaths: decreases population size

Population Growth Patterns

Population Growth Equation

The equation for population growth is

ΔN/Δt = bN-dN

N = population size b is per capita birth rate d is per capita death rate. ΔN/Δt is change in population N over a small time period t.

The per capita rate of population increase is symbolized by r.

r = b-d

r indicates whether a population is growing (r >0) or declining (r<0).

Calculating Population Growth

Population Growth Equation

Population growth is a function of the environment. The rate of growth for a population is directly determined by the amount of resources available.

Ecologists express instantaneous population growth using calculus.

Zero population growth occurs when the birth rate equals the death rate r = 0.

The population growth equation can be expressed as:

dNdt

rN

Calculating Population Growth

The exponential growth model describes population growth in an idealized, unlimited environment.

During EPG the rate of reproduction is at its maximum.

The equation for exponential population growth is:

Exponential Population Growth

Exponential growth cannot be sustained for long in any population.

A more realistic population model limits growth by incorporating carrying capacity.

Carrying Capacity (K) is the maximum population size the environment can support given its available resources.

Incorporating carrying capacity produces a logistic growth model, where the per capita rate of increase declines as carrying capacity is approached.

We construct the logistic model by starting with the exponential model and adding an expression that reduces the per capita rate of increase as N increases.

Carrying Capacity

Incorporating Carrying Capacity into the Population Growth Model

The logistic growth equation includes K, the carrying capacity (number of organisms environment can support):

As population size (N) increases, the equation ((K-N)/K) becomes smaller which slows the population’s growth rate.

Logistic Population Growth

As resources become less available, the growth of a population slows or stops. The general S shaped curve of this growth pattern is called logistic growth.

Logistic growth occurs when a population’s growth slows or stops following a period of exponential growth. Can slow when the birthrate decreases, the death rate

increases, or when both occur at the same rate Can slow when the rate of immigration decreases, the rate

of emigration increases, or both Can slow as the population encounters a limiting factor

The point at which carrying capacity line intercepts the y axis tells you the size of the population when the average growth rate is zero.

That number represents the largest number of individuals that a given environment can support (carrying capacity).

Logistic Population Growth

1

2

3

Phases of Logistic Growth

Graphs of Population Growth

Limits to Growth Limiting Factors are those factors that causes

population growth to decrease or stop. These factors may be classified as either density-

dependent or density-independent, depending on whether or not they become limiting only in large populations – or-- if they limit growth in all populations regardless of size.

Limits to Population Growth

Density Dependent factors – include disease, competition, parasites and food. These have an increasing effect as the population increases in size.

Density Independent factors – affect all populations regardless of their size. Most are abiotic factors such as temperature, storms, floods, droughts and habitat destruction.

In density-independent populations, birth rate and death rate do not change with population density. For example, in dune fescue grass environmental conditions kill a similar proportion of individuals regardless of density.

In density-dependent populations, birth rates fall and death rates rise with population density. Density-dependent population regulation much more common than density- independent.

Types of Limiting Factors

Competition: as a population becomes denser, the resources are used up at a much faster rate, limiting how large the population can grow.

Predation: the population of a predator can be limited by the available prey, and the population of prey can be limited by being caught for food.

Parasitism & Disease: these spread more quickly through dense populations because crowded areas make it easier for parasites or diseases to move from one carrier to the next. The parasites and disease can then cause the population size to decrease.

Density Dependent Limiting Factors

Predation Can Affect Population Sizes

The Predator-Prey Relationship

Weather: weather can affect the size of a population regardless of its density.

Natural disasters: volcanoes, tsunamis, tornados and hurricanes can wipe out populations regardless of density.

Human activities: human influence as a limiting factor has had a profound effect on populations worldwide, regardless of the density of those populations. These activities include destruction of habitats, urbanization, pollution, damming rivers, clear cutting forests, etc.

Density Independent Limiting Factors

What Limits Population Growth? http://www.classzone.com/cz/books/bio_07/

resources/htmls/animated_biology/unit5/bio_ch14_0449_ab_popgrow.html

Animated Biology

Data Analysis: Reading Combination Graphs

Critical Thinking Activity

Complete the data analysis activity on page 442 in your

virtual textbook. These activities are excellent ways

to practice application of concepts at home!

AKS Standards11c - relate environmental conditions to primary and secondary successional changes in ecosystems

Ecosystems are constantly changing in response to natural and human disturbances.

As an ecosystem changes, older inhabitants gradually die out and new organisms move in, causing further changes in the community.

This series of predictable changes that occurs in a community over time is called ecological succession: Can result from slow changes in the physical

environment Can result from sudden natural disturbances

Ecological Successions

Primary Succession Occurs as new ecosystems are developing in

areas where NO SOIL currently exists. Secondary Succession

Are the result of changing an existing ecosystem WITHOUT REMOVING EXISTING SOIL.

Types of Successions

Primary Successions

Secondary Successions

Inferring & Predicting Does the process of primary succession take

longer in tropical or arctic areas? Explain. During succession, what might become the

limiting factor for sun-loving mosses as taller plants begin to grow?

Primary succession takes longer in arctic areas because rock is covered with snow part of the year, the growing season is shorter, and cold temperatures slow growth and decomposition. Soil takes much longer to form.

The amount of sunlight becomes the limiting factor.

Critical Thinking Activity