Chapter 8Populations

Population Properties

The numbers or population of an organism is limited by their environment

Population- all the members of a species living in the same area at the same time

Ex: all the oak trees in Houston County

Properties

Can be described by:

Population size

Population Density

Patterns of dispersion

Demographics

Population growth

Limits on population growth

Terms to Know

Population size- number of individuals present living in a defined area

Population Density- number of individuals in a population per unit area

Population dispersion or distribution- the spatial arrangement of organisms within a particular area

Sex ratio- proportion of males to females

Distribution Patterns

Populations may be distributed in different ways:

1. Random- individuals located haphazardly in no particular pattern (minimal interaction)

Individuals are independent of others

Can occur when resources are found throughout an area

Distributions

2. UNIFORM DISTRIBUTION

Individuals are evenly spaced, same distance apart

Can occur when individuals hold territories or compete for space

Ex: plants in the desert need certain amount of “root” space to get water they need

Distributions

3. CLUMPED DISTRIBUTION

Most common in nature

Organisms arrange themselves according to the availability of resources

Organisms interact and are attracted to certain areas

Ex: Bees and flowering plants, breeding pools, humans to urban areas

Distribution Patterns

Age Distribution/Structure

Describes the relative numbers of organisms of each age within a population

Can make predictions based on age structure

Ex: Population past reproductive age will decline over time

Population pre-age or at age of reproduction- will likely increase

Even age distribution – remain stable

Age Structure Diagrams

Survivorship: percent of members likely to survive

Growth rate: birth & death rates, change in size

Growth rate= birth rate – death rate

Rate can be zero (no increase); negative (decrease); or positive (exceeds death rate)

Age Structure Diagram

Graphs

Survivorship Factors

Determined by 4 factors:

1.) Births (natality)

2.) Deaths (mortality)

3.) Immigration – arrival on individuals outside the population

4.) Emigration – departure of individual from the population

Survivorship Types

K-selected

Devote large amounts of energy and resources to caring for a few offspring

Tend to stabilize over time at or near their Carrying Capacity

K is abbreviation for Carrying Capacity

r-selected

Devote their energy and resources to producing as many offspring as possible in a short time

Survivorship is left to chance

Exponential Growth

Exponential Growth

Occurs when a population or anything else, increases by a fixed percentage each year

Occurs when pop. has plenty of food, space and limited competition or predators

Limiting Factors

Anything that Restrain population growth

Carrying Capacity- the maximum pop. size of a species that a given environment can sustain

Carrying Capacity Graph

r-selected vs K-selected

Exponential vs Logistic

Logistic Growth (Curve)(Carrying Capicity)

limiting factors = environmental resistance

Space, food, water, shelter, disease, predators, temp. mates/breeding sites

Plants: sunlight, moisture, soil

Aquatic: salinity, sunlight, temp, dissolved oxygen, and pollutants

Limits to Pop. Growth

Density Dependent: depends on size of the population

Increases and decreases with population density

Can help find mates, but increases:

Competition

Predation

Disease and Parasitism

Limits to Pop. Growth

Density Independent

Limiting factors that affect the population regardless of size (density)

Can eliminate large #’s of individuals without regard to their density

Examples:

Climate/Temperature extremes

Natural/Catastrophic events or disasters

Human Activity

Chapter 8: Species Interactions And Community Ecology

Standard 3 - Communities

CLE3255.3.1 – Ecological niches and various

habitats

CLE3255.3.2 – Species interactions, predation

competition = symbiotic relationships

Organisms Niche

Includes species habitat use, its role in the community, consumption of foods, use of resources, role in food chain/food web, and it’s interactions with other organisms

Summary of everything an organism does in its environment

Types of Niches

Fundamental Niche

The full niche of a species

No competitors

Fulfills all its roles or uses all resources it can and capable of using

Realized Niche

Plays only a part of its (species) role

Forced to use fewer resources due to competition or other species interactions

Competitors restrict what an organism can do or what resources it can use

Chart – Fig. 6.2, pg. 143

Species Relationships

When 2 organisms living in close association with each other interact = Symbiotic relationship

In symbiosis, at least one of the organisms usually benefits from the relationship

Species Interactions

Types:

Competition

Predation

Parasitism

Herbivory

Mutualism

Commensalism/Amensalism

Competition

Occurs when more than one species is seeking or attempting to use the same limited resource

Can take place in 2 ways:

Intraspecific Competition – competition among members of the same species

Interspecific Competition – competition among members of two or more different species

Consequences of Competition

Competition Exclusion – when one species excludes another species from resource use entirely

Species Coexistence – when neither species fully excludes the other, live in equilibrium;

*use resources at different times of the day or different levels

Resource Partitioning – the species partition or divide the resources they use in common

Character displacement – evolve physical characteristics that reflect their portion of resource use, natural selection; *Ex: birds eat same type of seed – one eats the smaller, the other the larger seeds

Larger seeds = bigger beak; Smaller seeds = smaller beak (Darwin’s Finches)

Predation

Process in which a (predator) hunts, captures, kills, and eats another organism (prey); *one benefits/one harmed

The primary organization forces and influence in community ecology

These interactions structure/influence food chains/webs, community make up, numbers and abundance of the predator and prey; creates cycles in populations

Predation

Adaptations of Predation

Camouflage: blending in with environment

Warning coloration: black stripes or red, orange and yellow

Mimicry: imitates another organisms warning coloration

Protective covering: quills, shells, exoskeleton

Odors/Poisons/Inks: skunks, snakes, octopus

Flying

Parasitism

Relationship in which one organism (parasite) depends on another (host) for nourishment, while doing the host harm

Some parasites cause little harm, while others kill

Some parasites live in close contact with the host; ticks, tapeworm, and lampreys

Others are free-living and come into contact with the host infrequently

Herbivory

* When animals feed on the tissues of plants

Insects that feed on plants are the most widespread type

Some plants recruit animals as allies to help in defense

Mutualism

Relationship in which 2 or more species benefits from the interaction with each other

Bacteria in our intestines

Acacia trees and ants – trees provide shelter, the ants defend and protect the trees

Commensalism and Amensalism

Commensalism: one species benefits, the other is neither harmed or helped (unaffected); *Sharks and remora’s: remora’s attach to sharks and feed on scraps of food; clown fish/sea anemome

Amensalism: one species is harmed and the other is neither harmed or helped (unaffected); *Ex: black walnut tree that secretes chemical that kills neighboring plants, penicillin/bacteria

Energy/Biomass

Food webs: show relationships and energy flow

Keystone species: strong impact on community; secondary and tertiary consumers

Community that resists change and remains stable; shows resistance

A community that changes in response to disturbance then returns to original state; shows resilience