Chapter 52-55 Ecology. A population is a group of individuals of a single species that simultaneously occupy the same general area. Characteristics of.

Chapter 52-55 Ecology

• A population is a group of individuals of a single species that simultaneously occupy the same general area.

Characteristics of a Population

Populations may increase in either of these 2 ways

• Population Density: # of individuals per unit

(ex: # people/square miles)

• Population Dispersion: how individuals are arranged or dispersed (even, clumped, random)

• Mark and recapture: used to estimate population size .

– Individuals are trapped in an area and captured, marked with a tag, recorded, and then released.

– After a period of time has elapsed, traps are set again, and individuals are captured and identified.

*Why do we care about estimating a population size?

• Additions occur through birth, and subtractions occur through death.– Demography studies the vital statistics that affect

population size.

– A graphic way of representing the data is a survivorship curve.

• This is a plot of the number of individuals in a cohort still alive at each age.

–A Type I curve shows a low death rate early in life (humans).

–The Type II curve shows constant mortality (squirrels).

–Type III curve shows a high death rate early in life (oysters).

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 52.3

Factors that effect reproductive potential

• Reproducing earlier in life• Generation time (average age of reproduction)• Gestation Period: the time in which a fetus

develops (mammals)

(elephants – 22 months!)

Population Growth• Population Growth Rate:

Birth rate – death rate

Biotic Potential: the fastest rate at which a population can grow

Reproductive Potential: the maximum number of offspring an individual can produce (in lifetime)

Who has a bigger reproductive potential: Bacteria or elephants?

Exponential Growth• Exponential Growth:

Population significantly increases with each generation

Occurs with unlimited resources and no competitors/predators

R-selection: growth that occurs when birth rates are high

Fig. 52.9


Carrying Capacity• Carrying Capacity: the maximum population

an ecosystem can support.

• Logistical Growth: in a population, the initial growth is exponential, then the growth slows and eventually stops

• K-selection: growth that incorporates the effect of population density on rate of increase

Fig. 52.11

Population Growth Models

• Exponential model (red) • idealized population in an unlimited environment (J-curve); r-selected species (r=per capita growth rate)

• Logistic model (blue) •carrying capacity (K): maximum population size that a particular environment can support (S-curve); K-selected species

• The logistic population growth model and life histories.– This model predicts different growth rates for

different populations, relative to carrying capacity.• Resource availability depends on the situation.• The life history traits that natural selection favors may

vary with population density and environmental conditions.

• In K-selection, organisms live and reproduce around K, and are sensitive to population density.

• In r-selection, organisms exhibit high rates of reproduction and occur in variable environments in which population densities fluctuate well below K.

Population life history “strategies”

• r-selected (opportunistic)

• Short maturation & lifespan

• Many (small) offspring; usually 1 (early) reproduction; no parental care

• High death rate

• K-selected (equilibrial)

• Long maturation & lifespan

• Few (large) offspring; usually several (late) reproductions; extensive parental care

• Low death rate

• Why do all populations eventually stop growing?

• What environmental factors stop a population from growing?

• The first step to answering these questions is toexamine the effects of increased population density.

Some questions…

Two Types of Population Regulation

• Density Dependent: A more crowded population causes more deaths (ex: starvation, predation, disease)

• Density Independent: A certain percent of a population dies regardless of the population density (ex: severe weather, natural disaster)

http://www.youtube.com/watch?v=BSVbdaubxxg&NR=1



• The Demographic Transition.– A regional human population can exist in one of

2 configurations.

• Zero population growth = high birth rates – high death rates – where?

• Zero population growth = low birth rates – low death rates- where?

– The movement from the first toward the second state is called the demographic transition.


Fig. 52.21


Fig. 52.22

• Predictions of the human population vary from 7.3 to 10.7 billion people by the year 2050.– Will the earth be overpopulated by this time?

Earth’s Carrying Capacity?

• Wide range of estimates for carrying capacity.– What is the carrying capacity of Earth for

humans?– This question is difficult to answer.

• Estimates are usually based on food, but human agriculture limits assumptions on available amounts.

• Ecological footprint.– Humans have multiple constraints besides food.– The concept an of ecological footprint uses the

idea of multiple constraints.

• For each nation, we can calculate the aggregate land and water area in various ecosystem categories.

• Six types of ecologically productive areas are distinguished in calculating the ecological footprint:– Land suitable for crops.

– Pasture.

– Forest.

– Ocean.

– Built-up land.

– Fossil energy land.

Community structure• Community~ an assemblage of

populations living close enough together for potential interaction

Interactions

• Interspecific (interactions between populations of different species within a community):

The Niche

• Ecological niche~ the sum total of an organism’s use of biotic and abiotic resources

in its environment; its “ecological role”

√ fundamental~ the set of resources a population is theoretically capable of using

under ideal conditions √ realized~ the resources a population actually uses

• Thus, 2 species cannot coexist in a community if their niches are identical

Ex: Barnacle sp. on the coast of Scotland

• Resource partitioning~ sympatric species consume slightly different foods or use other resources in slightly different ways

Ex: Anolis lizard sp. perching sites in the

Dominican Republic

Relationships• Trophic structure / levels~ feeding

relationships in an ecosystem

• Primary producers~ the trophic level that supports all others; autotrophs

• Primary consumers~ herbivores

• Secondary and tertiary consumers~ carnivores

• Detrivores/detritus~ special consumers that derive nutrition from non-living organic matter

• Food chain~ trophic level food pathway

Grass Insect Bird Fox

Where does the initial energy come from?

How does each organism obtain their energy?

This is a food chain

A food chain is a sequence in which energy is transferred from one organism to the next as each organism eats another organism

Food Chains

Food Webs

• Food webs are interconnected food chain that show many feeding relationships

hawk

Bird snake

mouse insect

seeds pine tree

- The arrows show the FLOW OF ENERGY

Energy Pyramid• Review 10% law

• Dominant species are those in a community that have the highest abundance or highest biomass (the sum weight of all individuals in a population).– If we remove a dominant species from a

community, it can change the entire community structure. (often plants)

Dominant species and keystone species exert strong controls on

community structure

Keystone Species

• Keystone species: a species that has a major impact and role within an ecosystem. Without them the ecosystem will fall apart.– Sea otter(Decrease Sea Otter Increase sea urchin-

Decrease Kelp- Decrease Fish spawning

• Disturbances are events like fire, weather, or human activities that can alter communities. – Some are routine.

Most communities are in a state of nonequilibrium owing to disturbances

Fig. 53.16

• We usually think that disturbances have a negative impact on communities, but in many cases they are necessary for community development and survival.

Fig. 53.18


• Human activities cause more disturbance than natural events and usually reduce species diversity in communities.

Give examples

Humans are the most widespread agents of disturbance

Succession

• Ecological succession~ changes to an ecosystem over time

• Primary~ begun in lifeless area; no soil, perhaps volcanic activity or retreating glacier

• Secondary~ an existing community has been cleared by some disturbance that leaves the soil intact (fire)

Primary Succession In I Am Legend

Secondary Succesion

Ecosystems

• All of the biotic and abiotic factors in an area

• The autotrophs are the primary producers, and are usually photosynthetic (plants or algae).– They use light energy to synthesize sugars and other

organic compounds.

Trophic Relationships

• Heterotrophs areat trophic levelsabove the primaryproducers anddepend on theirphotosyntheticoutput.

Fig. 54.1

– Herbivores that eat primary producers are called primary consumers.

– Carnivores that eat herbivores are called secondary consumers.

– Carnivores that eat secondary producers are called tertiary consumers.

– Another important group of heterotrophs is the detritivores, or decomposers.

• They get energy from detritus, nonliving organic material and play an important role in material cycling.

• The amount of light energy converted to chemical energy by an ecosystem’s autotrophs in a given time period is called primary production. (very important to an ecosystem)

Primary Production

• Production in Marine ecosystems.– Light is the first

variable to controlprimary productionin oceans, sincesolar radiationcan only penetrateto a certain depth(photic zone).

In aquatic ecosystems, light and nutrients limit primary production

Fig. 50.22

–In the open ocean, nitrogen and phosphorous levels are very low in the photic zone, but high in deeper water where light does not penetrate.

Fig. 54.5

• Nitrogen is the one nutrient that limits phytoplankton growth in many parts of the ocean.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 54.6

• Production in Freshwater Ecosystems.– Solar radiation and temperature are closely linked

to primary production in freshwater lakes.


– During the 1970s, sewage and fertilizer pollution added nutrients to lakes, which shifted many lakes from having phytoplankton communities to those dominated by diatoms and green algae.

• This process is calledeutrophication,and has undesirableimpacts from a human perspective.

Impacts of Eutrophication• Algal blooms block light available to other

plants

• When algae die, decompose and deplete dissolved oxygen creating dead zones

• Controlling pollution may help control eutrophication.

–Experiments are being done to study this process.


Fig. 54.8

Chemical Cycling• Biogeochemical cycles: the various nutrient circuits, which involve both abiotic and

biotic components of an ecosystem

• Water

• Carbon

• Nitrogen

• Phosphorus

Human Impact• Biological magnification: trophic process

in which retained substances become more concentrated at higher levels

• Greenhouse effect and climate change : warming of planet due to atmospheric accumulation of carbon dioxide

• Ozone depletion: effect of chlorofluorocarbons (CFC’s) released into the atmosphere, deplete ozone

• Rainforest destruction • Cause: Overpopulation?

• Conservation biology is a goal-oriented science that seeks to counter the biodiversity crisis, the current rapid decrease in Earth’s variety of life.

• Extinction is a natural phenomenon that has been occurring since life evolved on earth.– The current rate of extinction is what underlies the

biodiversity crisis.

– A high rate of species extinction is being caused by humans.

Conservation Biology


What is biodiversity?• Biodiversity: the total of genetically different

organisms in an area

A lot of biodiversity: Rainforest

Levels of Diversity

• Species diversity: # of different species in an area

• Ecosystem diversity: the variety of habitats, communities within an ecosystem

• Genetic Diversity: different genes within a population

• Loss of genetic diversity.– If a local population becomes extinct, then the

entire population of that species has lost some genetic diversity.

• The loss of this diversity is detrimental to the overall adaptive prospects of the species.

• Loss of species diversity.– The U.S. Endangered Species Act (ESA) defines

an endangered species as one in danger of extinction throughout its range, and a threatened species as those likely to become endangered in the foreseeable future.

• Loss of ecosystem diversity.– The local extinction of one species, like a

keystone predator, can affect an entire community.

– Some ecosystems are being erased from the Earth at an unbelievable pace.

• For example, an area the size of the state of West Virginia is lost from tropical forests each year.

Biodiversity: Human welfare

• 25% of all medical prescriptions

• Genetic variability• Aesthetic and ethical

reasons• Species survival

Biodiversity crisis- 4 major threatsMajor Threats:

1. Habitat destruction ~ single greatest threat; cause of 73% of species designation as extinct, endangered, vulnerable, rare; 93% of coral reefs


2.Competition by exotic (non-native) or invasive species – species that humans move from native locations to new geographic locations

- What are the problems associated with this?


3. Overexploitation ~ commercial harvest or sport fishing; illegal trade, hunting.

• The African elephant has been overhunted and the populations have declined dramatically.

• The bluefin tuna is another example of an over-harvested species.


Fig. 55.9

• Disruption of food chains.– The extinction of one species can doom its

predators, but only if the predator feeds exclusively on this prey.

Conservation biology focus• Preservationism: setting side select

areas as natural and underdeveloped

Nature Reserves

Population & species level conservation

• Biodiversity hot spot: small area with an exceptional concentration of species

• Endemic species: species found nowhere else

• Endangered species: organism “in danger of extinction”

• Threatened species: likely to become endangered in the foreseeable future

• Bioremediation: use of living organisms to detoxify polluted systems

Chapter 52-55 Ecology. A population is a group of individuals of a single species that simultaneously occupy the same general area. Characteristics of.

Documents

ecologya population

population densities

maximum population size

effect of population

logistical growth

initial growth

different growth rates

growth ratelogistic