Chapter 33, pg. 678-693

Population Growth and Regulation

33.1 Scope of Ecology What does the discipline of ecology study?

What levels of organization are studied in ecology?

What are 2 opposing models to explain community composition?

What is ecological succession? Explain.

Ecology: study of relationships among living organisms and the interactions they have with environment

Introduction

1. Individual: how they are adapted to their environment

2. Population: individuals of a same species that share the same geographical location at the same time How the size changes over time

3. Community: group of interacting populations occupying the same geographic area at the same time Effects of extrinsic and intrinsic factors on

these populations

Levels of Organization

4. Ecosystem: biological community and all abiotic factors that affect it

5. Biome: large group of ecosystems that share the same climate and have similar types of communities

6. Bioshpere: all biomes on Earth Air, land, and water

Composition: the populations within the community

Diversity: both the number of different populations and the relative abundance of individuals

The greater the diversity, the greater the number and the more even the populations!

Community Composition and Diversity

Question: Why do populations assemble together in the same place at the same time?

Interactive Model Community is highest level of organization

(cell, tissue, organism, population, community)

Populations dependent on biotic interactions (ex. food chain)

Predicts that composition in a particular place will always be the same

Models of Community Composition

Individualistic Model Hypothesizes that populations assemble

according to species’ tolerance for abiotic factors

Less diversity up north due to conditions Predicts that compositions are not

constant; boundaries between communities are not distinct

Ecological Succession: change in community composition over time

Result of changing abiotic/biotic factors

There are 2 types of ecological succession: Primary Succession and Secondary Succession

Ecological Succession

establishing a community in an area of exposed rock without topsoil

Natural events (retreating glaciers) can scrape rock bare OR new rock could form after a volcanic eruption

Wind and rain carry spores of organisms, like lichens, to these areas

Lichens are a combination of fungus and algaeObtain nutrients from rocks by secreting

chemicals that break down the rock

Primary Succession

Each stage of primary succession is gradual and introduces different populations of micro-organisms, plants and animals that will compete for nutrient, moisture, and sunlight

As organisms decompose, they contribute more organic matter to the soil layerEventually, seeds of trees will germinate

1st trees usually requires lots of light (ex. deciduous trees of boreal forests)

The shade will change abiotic conditions as soil becomes cooler and more moistOnly shade tolerant plants will grow

As more niches are created, there is be greater diversity in organisms creating more complex food webs

Orderly and predictable change that takes place after a community of organisms has been removed but the soil remained intactresult of a disturbance to an area that already

has soil and was once the home of living organisms

Secondary Succession

Occurs much faster than primary succession because soil and nutrients already exist

Often depends on the recovery of existing plants, such as trees, and on species that can rapidly reproduce in new conditions of increased sunlight and open areas Pioneer species often 1st to grow back

Succession’s end point can’t be predicted change at different rates; process can be

slow

1. Climax-Pattern Model: particular areas will always result in same type of community (a climax community) Based on observation that climate determines

growth Being modified – accept that exact composition

of community may not be the same

2. Facilitation Model: each stage is necessary for the next to occur No shrubs until the grasses have created

better soil

Models of Succession

3. Inhibition Model: colonists inhibit new growth until they are damaged or die

4. Tolerance Model: different types of plants can colonize at the same time Stages reflect amount of time needed for

species to mature

33.2 Population Characteristics and Growth Population size depends on what factors?

What are 2 patterns of population growth?

What is the purpose of a survivorship curve?

What trends are seen in the growth of the human population?

Population Density: number of organisms per unit area or volume

Usually expressed as “number of population” per “number of square unit” (metres, miles)

Population (or Spatial) Distribution: pattern of dispersal (or spacing) of a population within an area

3 types of patterns: uniform, clumped (or grouped), and random

Introduction

Limiting Factors: factors that determine whether an organism lives in a particular area

Usually determined by abiotic/biotic factors Amount of resources, predators, temperature,

etc. Ex. Trout will live in areas where the

water is cool and highly oxygenated

Populations have a certain size, and the size can stay the same from year to year, increase, or decrease , according to a per capita rate of increase. This considers the size of the population, birth rate, and death rate. It does not include immigration and emigration!

Example: A small town of 1000 people where 30 babies are born each year and 10 people die per year.

(30-10) / 1000 = 0.02 2% per year

Patterns of Population Growth

Biotic Potential: highest possible per capita rate of increase for a population

Will be high or low depending on usual number of offspring per reproduction, chances of survival until age o reproduction, how often each individual reproduces, and age at which reproduction begins

Exponential Growth: a J-shaped curves, can see how a population would explode if there were no limits (ex. insects)

Lag phase: growth is small because population is small

Exponential growth phase: growth accelerates, population exhibits biotic potential

Environmental Resistance typically stops exponential growth

includes the environmental conditions (food supply, waste products, competition) that prevent a population from growing too large.

growth will level off, creating a pattern of logistic growth.

Logistic Growth Model: Realistic model of population growth; S-shaped curve

Occurs when population growth slows when approaching carrying capacity (the amount that the environment can support)

Stops increasing when # of births < # of deaths OR when emigration > immigration

Lag phase: growth small because population small

Exponential growth phase: growth accelerates due to biotic potential

Deceleration phase: rate of growth slows Stable equilibrium phase: little, if any, growth

because births and deaths about equal

Cohort: members of an original group born at the same time and are still alive after certain intervals of time

3 types of curves: Curve I – typical of humans; most individuals

survive past midpoint and death occurs at the end of the life span

Curve II – typical of hydras; survivorship decreases at a steady rate throughout life span

Curve III – typical of oysters; most individuals die very young

Survivorship

Doubling Time: length of time needed for a population size to double

Estimated about 53 years

More Developed vs. Less Developed Countries MDC includes North America and Europe,

countries where population growth is low and good standard of living

LDC include Latin America, Africa, and Asia, countries where population growth is expanding and majority of people live in poverty

Human Population Growth

More Developed Countries...Doubled populations between 1850-1950

(decline in death rate, modern medicine, and improved socioeconomic conditions)

Modest growth between 1950-1975 (decline in birth rate)

Yearly growth now stabilized, some even declining

Sequence of events known as demographic transition

Less Developed Countries...Birth rate remained high after 1945 Demographic transition after 1965 (birth rate

fell and decline in death rate slowed

Methods to reduce the increase in human populations...

Establish/strength family planning programs; support from community leaders

Use social progress to reduce desire for large families (education, increased status of women, social improvements)

Delay onset of childbearing

Age Structure Diagrams: divide population into 3 groups – dependency, reproductive, and postreproductive

Ex. LDCs have more women entering reproductive years than older women leaving them

Zero Population Growth: no increase in the population size

Replacement Reproduction: causes most countries to continue growing due to age structure of population

If more young women enter reproductive years than older women leaving, growth will occur

Age Distribution

33.3 Regulation of population growth What are 2 life history patterns? What types of organisms exhibit each?

What density-independent factor aff ect population size?

What aff ect does competition have on the composition of a community?

How can predation aff ect the population densities of both predator and prey?

What are some eff ective anti-predator defenses?

What are the 3 types of symbiotic relationships? Explain.

There are 2 types of life history patterns:

1. Opportunistic Pattern: members are small in size, mature early, and have a short life span Produce small offspring and favour

greater numbers over parental care Classic Ex.: insects, weeds

Introduction

2. Equilibrium Pattern: size remains constant at carrying capacity Those who can compete most likely to

have large number of offspring Dedicate time/energy to their own

growth and survival and their offspring Fairly large slow to mature, and have a

fairly long lifespan Classic Ex.: whales, horses, etc.

REVIEW: In 33.2, we talked about some factors that limit exponential growth of population. These factors can be divided into 2 groups – density-independent and density-dependent factors!

Density-Independent Factors: Any factor in the environment that does NOT depend on the # of members in a population per unit area

Usually abiotic Include natural phenomena l – weather

like flooding, extreme heat/cold, and hurricanes

Typically regulates populations with opportunistic life patterns

Density-Dependent Factors: Any factor in the environment that depends on the number of members in a population per unit area

Often biotic factors predation, disease, parasites, and competition

Typically regulates populations with equilibrium life patterns

Competition

Competition: when 2+ organisms try to use limited resources at the same time

Competitive Exclusion Principle: no 2 species can occupy the same ecological niche at the same time if resources are limited

Habitat: an area where an organism lives

Niche: role or position that an organism has in its environment, including habitat and interactions

How it meets its needs for food, shelter, and reproduction

Could relate to living space, temperature, moisture, etc.

Resource Partitioning: decreases competition between the 2 species; even though similar species seem to occupy the sae niche, there are usually small differences

When grown in a test tube, 2 different paramecia can survive if one feeds on bacteria on the bottom of the tube while the other feeds from bacteria at the top

1 tree one bird species might eat insects on leave, while another eats insects on the bark

Predation: act of one organism (predator) consuming another (prey)

Ladybugs eating aphids (beneficial insects)

Parasitic ticks

Predation

Predator-Prey Population Dynamics: dynamic, not steady

Predator-prey relationships experience cyclesPredators overkill prey, resulting in

predator decline Prey population overshoots carrying

capacity then crashes, decreasing prey population

Antipredator Defenses: prey strategies to avoid predation

Ex. releasing poisonous chemicals to prevent ingestion, camouflage, warning coloration

Coevolution: occurs when 2 species adapt in response to one another

Acacia trees evolved long thorns to prevent grazing, so giraffes evolved long, prehensile tongues

Mimicry: one species resembles another to possess an antipredator defense

Can help predators hunt or prey avoid capture

Batesian mimicry – when prey mimics another species with a successful antipredator defense Ex. flies that look like wasps

Mullerian mimicry – when prey have the same defense Ex. stinging insects (bees, wasps, hornets) all have

black and yellow bands

Symbiotic Relationships: symbiosis is the close relationship between 2+ species

3 types of relationships: parasitism, commensalism, and mutualism

Symbiosis

Parasitism: where one organism (parasite) benefits while the other (host) is harmed

Can be external (fleas, ticks) or internal (bacteria, tapeworms)

Occurs in all kingdoms Host provides nourishment, and a place to

live/reproduce

Commensalism: relationship where 1 organism benefits while the other is neither helped nor harmed

Lichens grow on trees for better light access and do not harm the tree

sea anemones provide a home for clownfish

Mutualism: relationship between 2+ organisms that live closely together and benefit from each other

fungi provides a habitat for algae, which provide food

butterflies feed on flower nectar while pollinating the flowers

Cleaning Symbiosis: relationship where the individual being cleaned is a vertebrate and the cleaner is a crustacean/fish/bird