population dynamics ap environmental science population dynamics outline characteristics of a...

Population DynamicsPopulation Dynamics

AP Environmental ScienceAP Environmental Science

Population Dynamics OutlinePopulation Dynamics Outline

• Characteristics of a PopulationCharacteristics of a Population• Population Dynamics and Carrying Capacity

• Reproductive Strategies

• Conservation Biology

• Human Impacts

• Working with Nature

Characteristics of a PopulationCharacteristics of a Population

• Population - individuals inhabiting the same area at the same time

• Population Dynamics: Population change due to– Population Size - number of individuals– Population Density - population size in a certain

space at a given time– Population Dispersion - spatial pattern in habitat

Population SizePopulation Size• Natality

– Number of individuals added through reproduction– Crude Birth Rate - Births per 1000– Total Fertility Rate – Average number of children

born alive per woman in her lifetime

• Mortality– Number of individuals removed through death– Crude Death Rate Deaths per 1000

Population DensityPopulation Density

• Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area– Some species exist in high densities - Mice– Some species exist in low densities - Mountain lions

• Density depends upon– social/population structure– mating relationships– time of year

Population DispersionPopulation Dispersion

Population dispersion is the spatial pattern of distribution

There are three main classifications

Clumped: individuals are lumped into groups ex. Flocking birds or herbivore herds due to resources that are clumped or social interactions most common http://www.johndarm.clara.net/galleryphots/

Population DispersionPopulation DispersionUniform: Individuals are regularly spaced in the environment - ex. Creosote bush due to antagonism between individuals, or do to regular spacing of resources rare because resources are rarely evenly spaced

http://www.calflora.net/bloomingplants/creosotebush2.html

www.agry.purdue.edu/turf/ tips/2002/clover611.htm

Random: Individuals are randomly dispersed in the environment ex. Dandelions due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals rare because these conditions are rarely met

http://www.calflora.net/bloomingplants/creosotebush2.html

http://www.agry.purdue.edu/turf/tips/2002/clover611.htm

http://www.agry.purdue.edu/turf/tips/2002/clover611.htm


• Characteristics of a Population

• Population Dynamics and Population Dynamics and Carrying CapacityCarrying Capacity



• Human Impacts


• Biotic Potential– factors allow a population to increase

under ideal conditions, potentially leading to exponential growth

• Environmental Resistance – affect the young more than the elderly

in a population, thereby affecting recruitment (survival to reproductive age)

Biotic PotentialBiotic Potential• Ability of populations of a given species to

increase in size– Abiotic Contributing Factors:

• Favorable light

• Favorable Temperatures

• Favorable chemical environment - nutrients

– Biotic Contributing Factors:• Reproductive rate

• Generalized niche

• Ability to migrate or disperse

• Adequate defense mechanisms

• Ability to cope with adverse conditions

Environmental ResistanceEnvironmental Resistance• Ability of populations of a given species to

decrease in size– Abiotic Contributing Factors:

• Unfavorable light• Unfavorable Temperatures• Unfavorable chemical environment - nutrients

– Biotic Contributing Factors:• Low reproductive rate• Specialized niche• Inability to migrate or disperse• Inadequate defense mechanisms• Inability to cope with adverse conditions

The Rule of 70

• To find doubling time when you have the population growth rate:

• Take 70 divided by the growth rate = doubling time

70/% = doubling time

Example

• If the growth rate is 2%, what is the doubling time of the population?

• 70/2 =

Population GrowthPopulation Growth• Population growth depends upon

– birth rates– death rates– immigration rates (into area)– emigration rates (exit area)

Pop = Pop0 + (b + i) - (d + e)

ZPG (b + i) = (d + e)

Population GrowthPopulation Growth

• Populations show two types of growth– Exponential

• J-shaped curve• Growth is independent of population density

– Logistic • S-shaped curve• Growth is not independent of population

density

Exponential Population Growth

© Brooks/Cole Publishing Company / ITP

Exponential growth occurs when resources are not limiting.

• during exponential growth population size increases faster and faster with time;

• currently the human population is undergoing exponential growth;

• exponential growth can not occur forever because eventually some factor limits population growth.

Fig. 10–4a

Limiting Factors

Density Dependent Factors

• Food

• Water

• Predators

• Disease

Density Independent Factors

• Weather

Population Dynamics and Carrying Population Dynamics and Carrying CapacityCapacity

• Basic Concept: Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths)– There is a dynamic balance between

biotic potential and environmental resistance

Carrying Capacity (K)Carrying Capacity (K)

• Exponential curve is not realistic due to carrying capacity of area

• Carrying capacity is maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability)

Logistic GrowthLogistic Growth• Because of Environmental Resistance,

population growth decreases as density reaches carrying capacity

• Graph of individuals vs. time yields a sigmoid or S-curved growth curve

• Reproductive time lag causes population overshoot

• Population will not be steady curve due to resources (prey) and predators

• A comparison of the logistic growth model and the exponential growth model

Figure 18.20

Carrying capacity

Exponential growth

Logistic growth

Exceeding the Carrying Capacity


During the mid–1800s sheep populations exceeded the carrying capacity of the island of Tasmania. This "overshoot" was followed by a "population crash". Numbers then stabilized, with oscillation about the carrying capacity.

Fig. 10–5

Exceeding the Carrying Capacity


Reindeer introduced to a small island off of Alaska in the early 1900s exceeded the carrying capacity, with an "overshoot" followed by a "population crash" in which the population was totally decimated by the mid–1900s.

Fig. 10–5

Population Curves in Nature


Population cycles for the snowshoe hare and Canadian lynx are believed to result because the hares periodically deplete their food, leading to first a crash of the hare population and then a crash of the lynx population.

Fig. 10–8



• Population Dynamics and Carrying Capacity

• Reproductive StrategiesReproductive Strategies• Conservation Biology

• Human Impacts


Reproductive StrategiesReproductive Strategies• Goal of every species is to produce as many

offspring as possible• Each individual has a limited amount of

energy to put towards life and reproduction• This leads to a trade-off of long life or high

reproductive rate• Natural Selection has lead to two strategies for

species: r - strategists and K - strategists

r - Strategistsr - Strategists• Spend most of

their time in exponential growth

• Maximize reproductive life

• Minimum life

K

R StrategistsR Strategists• Many small offspring• Little or no parental care and protection of offspring• Early reproductive age• Most offspring die before reaching reproductive age• Small adults• Adapted to unstable climate and environmental

conditions• High population growth rate – (r)• Population size fluctuates wildly above and below

carrying capacity – (K)• Generalist niche• Low ability to compete• Early successional species

K - StrategistsK - Strategists

• Maintain population at carrying capacity (K)

• Maximize lifespan

K

K- StrategistK- Strategist• Fewer, larger offspring• High parental care and protection of offspring• Later reproductive age• Most offspring survive to reproductive age• Larger adults• Adapted to stable climate and environmental

conditions• Lower population growth rate (r)• Population size fairly stable and usually close to

carrying capacity (K)• Specialist niche• High ability to compete• Late successional species

Survivorship Curves


Three kinds of curves:

• late loss (usually K–strategists), in which high mortality is late in life;

• constant loss (such as songbirds), in which mortality is about the same for any age;

• early loss (usually r–strategists), in which high mortality is early in life. Fig. 10–9

Population Curves in Nature


Natural populations display a broad diversity of population curves. Stable populations are relatively constant over time. Cyclic curves are often associated with seasons or fluctuating resource availability. Irruptive curves are characteristic of species that only have high numbers for only brief periods of times (e.g., seven–year cicada).

Fig. 10–6





• Conservation BiologyConservation Biology• Human Impacts


Conservation BiologyConservation Biology

• Three PrinciplesThree Principles1. Biodiversity and ecological integrity are

useful and necessary to all life on earth and should not be reduced by human actions

2. Humans should not cause or hasten the premature extinction of populations and species or disrupt vital ecological processes

3. Best way to preserve earth’s biodiversity and ecological integrity is to protect intact ecosystems that provide sufficient habitat

Habitat FragmentationHabitat Fragmentation• Process by which human activity

breaks natural ecosystems into smaller and smaller pieces of land

• Greatest impact on populations of species that require large areas of continuous habitat

• Also called habitat islands

1949 1964

Habitat fragmentation

in northern Alberta

1982 1991






• Human ImpactsHuman Impacts• Working with Nature

Human ImpactsHuman Impacts

• Fragmentation and degrading habitat

• Simplifying natural ecosystems

• Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides

• Elimination of some predators

Human Impacts on Ecosystems


Some major human impacts on ecosystems:

• fragmenting and degrading habitat;

• simplifying natural ecosystems;

• strengthening some populations of pest species and disease–causing bacteria by speeding natural selection and causing genetic resistance through overuse of pesticides and antibiotics;

• eliminating some predators;

• deliberately or accidentally introducing new species;

• overharvesting potentially renewable resources;

• interfering with chemical cycling and energy flows.






• Human Impacts

• Working with NatureWorking with Nature

Working with NatureWorking with Nature

• Learn six features of living systems– Interdependence– Diversity– Resilience– Adaptability– Unpredictability– Limits

Basic Ecological LessonsBasic Ecological Lessons1. Sunlight is primary source of energy

2. Nutrients are replenished and wastes are disposed of by recycling materials

3. Soil, water, air, plants and animals are renewed through natural processes

4. Energy is always required to produce or maintain an energy flow or to recycle chemicals

Basic Ecological LessonsBasic Ecological Lessons5. Biodiversity takes many forms because it has

evolved over billions of years under different conditions

6. Complex networks of + and – feedback loops exist

7. Population size and growth rate are controlled by interactions with other species and with abiotic

8. Organisms generally only use what they need

Four Principles for SustainableFour Principles for Sustainable

1. We are part of, not apart from, the earth’s dynamic web of life.

2. Our lives, lifestyles, and economies are totally dependent on the sun and the earth.

3. We can never do merely one thing (first law of

human ecology – Garret Hardin).

4. Everything is connected to everything else; we are all in it together.

population dynamics ap environmental science population dynamics outline characteristics of a...

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