ECOLOGY A study of the interactions of living organisms and the environment in which they live.

ECOLOGY

A study of the interactions of living organisms and the

environment in which they live

Ecology is the scientific study of the interactions between organisms and their environment.

A. Introduction

The environment of any organism includes the following components:

–Abiotic factors: non-living chemical and physical factors such as temperature, light, water, and nutrients

–Biotic factors: the living components

Temperature: some organisms can only tolerate specific ranges of temperature.

Water: some organisms can only tolerate either fresh or salt water.

Sunlight provides energy that drives nearly all ecosystems.– The intensity and quality of light, and

photoperiod can be important to the development and behavior of many organisms.

B. Abiotic factors affect the distribution of organisms

Wind amplifies the effects of temperature by increasing heat and water loss (wind-chill factor).

Rocks and soil: the physical structure and mineral composition of soils and rocks limit distribution of plants and the animals that feed upon them.

Organismal ecology is concerned with the behavioral, physiological, and morphologicalways individualsinteract with theenvironment.

C. Approaches to studying ecology…

Fig. 50.2a

Population ecology: a population is a group of individuals of the same species living in a particular geographic area.

An example of a population could be gray squirrels living in Sea Cliff.

– Population ecology examines factors that affect population size and composition.

Community ecology:a community consists of all the organisms ofall the species thatinhabit a particulararea. (all biotic)

An example of a community could be gray squirrels, raccoons, cardinals, chipmunks, and black crows living in Glen Head. Fig. 50.2c

Ecosystem ecology: an ecosystem consists of all the abiotic factors in addition to the entire community of species that exist in a certain area.

Example? All bullfrogs, minnows, snails, snapping turtles, algae in a pond and how ph, temperature, sunlight impact this life

Marine biomes have a salt concentration of approximately 3% and cover approximately 75% of the earth’s surface.

– Freshwater biomes are usually characterized by salt concentration of less than 1% and are closely linked to the soils and biotic components of the terrestrial biomes through which they pass.

D.Biomes can be aquatic or

terrestrial

Freshwater biomes (ponds and lakes, small and large freshwater).

The littoral zone is shallow and close to shore. The limnetic zone is the open surface water. The profundal

zone consistsof the deep,aphotic regions.

Lakes–Oligotrophic lakes are deep, nutrient-poor

and do not contain much life.

Eutrophic lakes are shallower and have increased nutrients.

Mesotrophic have a moderate amount of nutrients and phytoplankton productivity.–Over long periods of time,

oligotrophic lakes may become mesotrophic as runoff brings in nutrients.

–Pollution from fertilizers can cause explosions in algae population and cause a decrease in oxygen content.

Streams and rivers are bodies of water moving continuously in one direction.

Wetlands are areas covered with water that supports many types of plants.

They can be saturated or flooded and include areas known as marshes, bogs, and swamps.

They are home tomany differenttypes of organisms,from herbivoresto crustaceans.

Unfortunately,humans havedestroyed them,but many are nowprotected inmany places.

Fig. 50.21a

– Estuaries are areas where freshwater and salt water meet.The salinity of these areas can vary

greatly.They are crucial feeding areas for many

types of water fowl.

Zonation in Marine communities.

–The intertidal zone is where the land meets the water.

–The neritic zone includes the shallow regions over the continental shelves.

–The oceanic zone extends past the continental shelves, and can be very deep.

–The pelagic zone is the open water.

–The benthic zone is the seafloor.

Coral reefs exist in the neritic zone.– They constitute a

conspicuous anddistinctive biome.

– They are dominatedby coral and includea very diverseassortment ofvertebrates andinvertebrates.

E.The geographic distribution of terrestrial biomes is based mainly on

regional variations in climate

Vertical stratification is also important in these biomes.– The canopy of the tropical rain forest is the

top layer, covering the layers below.

– The permafrost in the tundra is a permanently frozen stratum that lies under ground.

Human activity has radically altered the natural patterns of many biomes.

Tropical forests are close to the equator, receive high amounts of rainfall (although this can vary from region to region), and contain a great variety of plants and animals.

The vegetation is layered, with the canopy being one of the top layers.

Savannas are grasslands with scattered trees, that show distinct seasons, particularly wet and dry.Fire is an important abiotic factor.

Deserts have low rainfall, and are generally hot.

Vegetation is usually sparse, and includes cacti and succulents.

Many animalsare nocturnal,so they canavoid the heat.

Fig. 50.25c

Chaparrals have mild wet winters and dry hot summers.

They containdense spiny,evergreenshrubs andhave periodicfires.

Some plantsproduce seedsthat will onlygerminateafter a fire.

Fig. 50.25d

Temperate grasslands exhibit seasonal drought, occasional fires, and are usually used for grazing and agriculture.

Temperate deciduous forests contain dense stands of trees and have very cold winters and hot summers.

The trees loseleaves and godormant in winter.

This biomeincludes a largevariety of plantsand animals.

Humans havelogged many ofthese forestsaround the world.

Fig. 50.25f

Coniferous forests (taigas) are the largest terrestrial biome on earth.– They exhibit long cold winters and short

wet summers.

Tundra contains low growing plants.– The climate is windy and cold which

causes a short growing season.– A layer of permafrost is found below 1

meter and does not thaw, which prevents root growth; not many animals live in tundra biomes.

– There are two types, arctic, which is found in areas of Alaska and the Arctic circle, and alpine, which is found on very high mountaintops.

Populations have size and geographical boundaries.– The density of a population is measured as

the number of individuals per unit area.– The dispersion of a population is the pattern

of spacing among individuals within the geographic boundaries.

F. Population ecology

Measuring density of populations is a difficult task.– We can count individuals; we can estimate

population numbers.

One sampling technique that researchers use is known as the mark-recapture method.

–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.

–This information allows estimates of population changes to be made.

Patterns of dispersion vary…Clumped xxx

xxxThis dispersion pattern is mostly due to resource distribution.

Uniform x x x x x x This dispersion pattern is due to direct interactions

between individuals such as competition for resources.

Random xx x xxx x xxxx This pattern is due to the absence of interactions

within a population.

Clumped dispersion is when individuals aggregate in patches.

By contrast, uniform dispersion is when individuals are evenly spaced.

In random dispersion, the position of each individual is independent of the others.

Click here- how to study biodiversity

Additions occur through birth, and subtractions occur through death.

– Demography studies the vital statistics that affect population size.

Life tables and survivorship curves.

– A life table is an age-specific summary of the survival pattern of a population.

G. Demography is the study of factors that affect the growth and

decline of populations

– 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).

Reproductive rates.

– Demographers that study populations usually ignore males, and focus on females because only females give birth to offspring.

– A reproductive table is an age-specific summary of the reproductive rates in a population.For sexual species, the table tallies the

number of female offspring produced by each age group.

To understand how much a population’s growth may be changing, birth and death rates must be considered.

H. Population Growth

Using mathematical notation we can express this relationship as follows:

– If N represents population size, and t represents time, then N is the change is population size and t represents the change in time, then:N/t = B-DWhere B is the number of births and D is

the number of deaths

– If B = D then there is zero population growth

– Under ideal conditions, a population grows rapidly.Exponential population growth is

said to be happeningUnder these conditions, we may

assume the maximum growth rate for the population (rmax) to give us the following exponential growth

dN/dt = rmaxN

Typically, unlimited resources are rare.

–Population growth is therefore regulated by carrying capacity (K), which is the maximum stable population size a particular environment can support.

I. The logistic model of population growth incorporates the concept of

carrying capacity

The logistic growth equation

– We can modify our model of population growth to incorporate changes in growth rate as population size reaches a carrying capacity.

– The logistic population growth model incorporates the effect of population density on the rate of increase.

The graph of this equation shows an S-shaped curve.

How well does the logistic model fit the growth of real populations?

– The growth of laboratory populations of some animals fits the S-shaped curves fairly well.

Different types of populations may show different life history strategies relative to their population growth.

In K-selection, organisms live and reproduce around K, and are sensitive to population density- they follow the logistic growth curve.

In r-selection, organisms exhibit high rates of reproduction and occur in variable environments in which population densities fluctuate- they follow an exponential growth curve for a period of time.

Who are r-selected and k-selected populations?

An example of an r-selected population is a group of mosquitoes in the spring.

An example of a k-selected population is a group of giraffes living on a savanna.

r-selected K-selected

Homeostatic capability

Limited Extensive

Maturation time

Short Long

Lifespan Short Long

Mortality rate

High Low

r-selected K-selected

# offspring and size/

reproductive episode

Many, small Few, large

# reproductions/lifetime

1 Several

Age at 1st reproduction

Early (young)

Late (older)

Parental care None Often extensive

Why do all populations eventually stop growing?

What environmental factors stop a population from growing?

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

J. How does density impact population growth?

Density-dependent factors increase their effect on apopulation as populationdensity increases.– This is a type of negative

feedback. Density-independent

factorsare unrelated to populationdensity, and there is nofeedback to slow populationgrowth.

Examples of density dependent factors include: disease, available food or territory, health, predation, pollution

Examples of density independent factors include hurricanes, tsunami, fires, & earthquakes

Some populations have regular boom-and-bust cycles.

– The populations of predators and their prey can fluctuate greatly.

The human population increased relatively slowly until about 1650 when the Plague took an untold number of lives.

– Ever since, human population numbers have doubled twiceHow might this population growth ever

stop?

K. The human population has been growing almost exponentially for three centuries but cannot do so

indefinitely

Age structure.

–Age structure is the relative number of individuals of each age.

–Age structure diagrams can reveal a population’s growth trends, and can point to future social conditions.

What can we learn from these graphs?

Kenya’s population Bulge in the young population means that most of these individual can reproduce in the future, although there is a high mortality rate at old age.

US population shows a bulge in the “baby boomers” and more of the population survives into old age.

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?

L. Estimating Earth’s carrying capacity for humans is a

complex problem

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.

–We may never know Earth’s carrying capacity for humans, but we have the unique responsibility to decide our fate and the fate of the rest of the biosphere.

Possible interspecific interactions exist in a community and can have positive or negative effects.

M. Community Ecology

Competition.

– Interspecific competition for resources can occur when resources are in short supply.There is potential for competition

between any two species that need the same limited resource.

– The competitive exclusion principle: two species with similar needs for same limiting resources cannot coexist in the same place.

– The ecological niche is the role an organism plays in an environment.For example, a squirrel’s niche would

include where it lives, the territory it covers, the other squirrels or other species it encounters, it’s mate, etc.….

The competitive exclusion principle can be restated to say that two species cannot coexist in a community if their niches are identical.

Classic experiments confirm this.

Predation.

– A predator eats prey.

– Predator adaptations: many important feeding adaptations of predators are both obvious and familiar.Claws, teeth, fangs, poison, heat-

sensing organs, speed, and agility.

– Plant defenses against herbivores include chemical compounds that are toxic.

– Animal defenses against predators.Behavioral defenses include fleeing,

hiding, self-defense, noises, and mobbing.

Camouflage includes cryptic coloration, deceptive markings.

Chemical defenses include odors and toxins

Aposematic coloration is indicated by warning colors, and is sometimes associated with other defenses (toxins).

Mimicry is when organisms resemble other species.

–Batesian mimicry is where a harmless species mimics a harmful one.

Fig. 53.7

Müllerian mimicry is where two or more unpalatable or harmful species resemble each other.

Fig. 53.8

Mutualism is where two species benefit from their interaction. (ie ants and the Acacia tree)

Commensalism iswhere one speciesbenefits from theinteraction, but otheris not affected.– An example

wouldbe barnacles thatattach to a whale.

In parasitism, predators

live on/in a host and depend

on the host for nutrition.

Example: a tick is a parasite to

a dog or human

– Coevolution refers to reciprocal evolutionary adaptations of two interacting species.When one species evolves, it

exerts selective pressure on the other to evolve to continue the interaction.

Example: many flowers have coevolved with the pollinators that are attracted to them.

The trophic structure of a community is determined by the feeding relationships between organisms.

The transfer of food energy from its source in photosynthetic organisms through herbivores and carnivores is called the food chain.

N. Trophic structure is a key factor in community dynamics

Click animation

Charles Elton firstpointed out that the length of a food chain is usually four or five links, called trophic levels.

He also recognizedthat food chains are not isolated units butare hooked togetherinto food webs.

Food webs.– Who eats whom

in a community?– A given species

may weave into the web at more than one trophic level.

Fig. 53.11

The autotrophs are the

primary producers, and are usually photosynthetic (plants or algae).

– They use light energy to synthesize sugars and other organic compounds.

Heterotrophs areat trophic levelsabove the primaryproducers anddepend on theirphotosyntheticoutput.

– Herbivores that eat primary producers are called primary consumers.

– Carnivores that eat herbivores are called secondary consumers.

– Carnivores that eat secondary consumers 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.

Food chains can be represented as food

pyramidsThe pyramid of energy:

Energy is transferred from the sun to producers to primary, secondary and then tertiary consumers.

There is a 10% transfer of energy from on level to the next.

Most energy is used for metabolism or lost as heat at each level.

Fig. 54.11

– The dynamics of energy through ecosystems have important implications for the human population.

Pyramid of biomass : Producers are greatest in biomass at the bottom of the pyramid….As you go up the food chain, biomass decreases

Most biomass pyramids narrow sharply from primary producers to top-level carnivores because energy transfers are inefficient.

Pyramids of numbers show how the number of individuals present in each trophic level decreases from producer to each level of consumer.

The organisms that feed as detritivores often form a major link between the primary producers and the consumers in an ecosystem.

The organic material that makes up the living organisms in an ecosystem gets recycled.

O. Decomposition connects all trophic levels

– An ecosystem’s main decomposers are fungi and prokaryotes (bacteria), which secrete enzymes that digest organic material and then absorb the breakdown products.

Ecological succession is the transition in species composition over ecological time.

Primary succession begins in a lifeless area where soil has not yet formed.

Example?

lichen moss grassshrubstrees

P. Ecological succession is the sequence of community changes

until a stable climax community is formed.

– Mosses and lichens colonize first and cause the development of soil.

– They are called the “pioneer species”

– The climax community is the last stable stage to appear.

– In NY state, the climax community consists of oak, maple and beach trees.

Ecological Succession

https://en.wikipedia.org/wiki/Ecological_succession

Secondary succession occurs where an existing community has been cleared by some event (ie fire,earthquake, volcanic eruption, hurricane), but the soil is left intact.

– Grasses grow first, then trees and other organisms.

animation

Comparing types of succession

http://mrswolfgang.wikispaces.com/file/view/3.muth.comparison.png/75233551/3.muth.comparison.png

Q. Ecosystems rely on cycles

Cycles include:

The water cycle

The carbon cycle

The nitrogen cycle

The phosphorus cycle

– The water cycle

The carbon cycle also includes hydrogen and oxygen.

animation

The nitrogen cycle.– Nitrogen enters ecosystems through two

natural pathways.Nitrogen from the atmosphere can

enter the soil by rain and dust.Nitrogen fixation, where certain

bacteria convert N2 to compounds in the soil that can be used to synthesize nitrogenous organic compounds like amino acids.

These archaebacteria are found on the root nodules of legumes like clover and represent a mutualism.

– The direct product of nitrogen fixation is ammonia, which picks up H + and becomes ammonium in the soil (ammonification), which plants can use.Certain aerobic bacteria oxidize

ammonium into nitrate, a process called nitrification.

Nitrate can also be used by plants.Some bacteria get oxygen from the

nitrate and release N2 back into the atmosphere (denitrification).

The phosphorus cycle.

–Organisms require phosphorus for many things.

–This cycle is simpler than the others because phosphorus does not come from the atmosphere.

The growing human population size coupled with technology that is not environmentally friendly leads to great disruptions in our ecosystems.

R. The human population is disrupting chemical cycles throughout the biosphere

n agricultural ecosystems, a large amount of nutrients are removed from the area in the crop biomass.After awhile, the natural store of

nutrients can become exhausted.

– Recent studies indicate that human activities have approximately doubled the worldwide supply of fixed nitrogen, due to the use of fertilizers, cultivation of legumes, and burning.This may increase the amount of

nitrogen oxides in the atmosphere and contribute to atmospheric warming, depletion of ozone and possibly acid rain.

Excess nitrogen can runoff into water systems, which leads to algae blooms, which ultimately leads to oxygen depletion after aerobic bacteria consume the dead algae.

This process is calledeutrophication

Controlling pollution may help control eutrophication.

The burning offossil fuelsreleases sulfuroxides and nitrogen thatreact with waterin the atmosphereto produce sulfuric and nitric acids.

S. Combustion of fossil fuels is the main cause of acid

precipitation

– These acids fall back to earth as acid precipitation, and can damage ecosystems greatly.

– The acids can kill plants, and can kill aquatic organisms by changing the pH of the soil and water.

Humans produce many toxic chemicals that are dumped into ecosystems.– These substances are ingested and

metabolized by the organisms in the ecosystems and can accumulate in the fatty tissues of animals.

– These toxins become more concentrated in successive trophic levels of a food web, a process called biological magnification.

T. Toxins can become concentrated in successive trophic levels of food webs

The pesticide DDT, before it was banned, showed this effect.

Rising atmospheric CO2.

– Since the Industrial Revolution, the concentration of CO2 in the atmosphere has increased greatly as a result of burning fossil fuels.

U. Human activities may be causing climate change by increasing carbon dioxide

concentration in the atmosphere

Measurements in 1958 read 316 ppm and increased to 370 ppm today

The greenhouse effect.– Rising levels of atmospheric

CO2 may have an impact on Earth’s heat budget.

– When light energy hits the Earth, much of it is reflected off the surface.CO2 causes the Earth to

retain some of the energy that would ordinarily escape the atmosphere.–This phenomenon is called

the greenhouse effect.

Global warming.Several studies predict a

doubling of CO2 in the atmosphere will cause a 2º C increase in the average temperature of Earth.

Rising temperatures could cause polar ice cap melting, which could flood coastal areas.

– It is important that humans attempt to stabilize their use of fossil fuels.

Life on earth is protected from the damaging affects of ultraviolet radiation (UV) by a layer of O3,or ozone.

Studies suggest thatthe ozone layer hasbeen gradually“thinning” since 1975.

V. Human activities are depleting the atmospheric

ozone

The destruction of ozone probably results from the accumulation of chlorofluorocarbons, chemicals used in refrigeration and aerosol cans, and in certain manufacturing processes.

– The result of a reduction in the ozone layer may be increased levels of UV radiation that reach the surface of the Earth.This radiation has been linked to

skin cancer and cataracts.

Why should we care about biodiversity?

How does it benefit us to maintain species diversity and genetic diversity?

W. Biodiversity is vital to human welfare

Biodiversity is acrucial naturalresource, andspecies that arethreatened couldprovide crops, fibers, and medicines forhuman use.

The loss of species also means the loss of genes.– Biodiversity represents the sum of

all the genomes on Earth.

Fig. 55.3

Habitat destruction– Human alteration of habitat is the

single greatest cause of habitat destruction.

– Destruction of physical habitat is responsible for the 73% of species designated extinct, endangered, vulnerable, or rare.

– About 93% of the world’s coral reefs have been damaged by humans.

X. The four major threats to biodiversity are habitat destruction, introduced species, overexploitation

and food chain disruption

Introduced species Introduced species are those

that humans move from native locations to new geographic regions.– The Nile perch was

introduced into LakeVictoria as a food fish,but led to the extinctionof several native species.

There are manyexamples of howexotic specieshave disruptedecosystems.

Overexploitation

– This refers to the human harvesting of wild plants and animals at rates that exceed the ability of those populations to rebound.

– The great auk was overhunted and became extinct.

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

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