Ecology of Organisms and Populations
Ch. 18
Ecology
Study of interactions between organisms and their environment
Ecology can be divided into four increasingly comprehensive levels: Organismal ecology Population ecology Community ecology Ecosystem ecology
Ecology
Organismal ecology Is concerned with
evolutionary adaptations that enable individual organisms to meet the challenges posed by their abiotic environments. http://www.seabird.org/assets/killer%20whales%20internet%202.jpg
Ecology
Population ecology Is concerned with
populations, groups of individuals of the same species living in the same area.
Concentrates mainly on factors that affect population density and growth.
http://newsimg.bbc.co.uk/media/images/44609000/jpg/_44609350_puffins512.jpg
Ecology
Community ecology Is concerned with
communities, assemblages of populations of different species.
Focuses on how interactions between species affect community structure and organization.
http://www.mass.gov/envir/forest/images/multiLayerForest.jpg
Ecology
Ecosystem ecology Is concerned with ecosystems, which include all the abiotic
factors in addition to the community of species in a certain area.
Focuses on energy flow and the cycling of chemicals among the various abiotic and biotic factors.
http://www.african-books.com/images/Animals/montage.jpg
Components of the Environment The abiotic component
Consists of nonliving chemical and physical factors.
The biotic component Includes the living factors.
Abiotic Factors of the Biosphere On a global scale, ecologists have recognized striking
regional patterns in the distribution of terrestrial and aquatic life.
Global distribution patterns Reflect regional differences in climate and other abiotic factors.
Sunlight
Solar energy powers nearly all ecosystems. Availability of sunlight affects aquatic and
terrestrial environments.
http://artfiles.art.com/images/-/Aflo/Sun-Shining-in-Blue-Sky-Over-Tree-in-Winter-Snow-Biei-Hokkaido-Japan-Photographic-Print-C13062664.jpeg
Water
Aquatic organisms may face problems with water balance.
For terrestrial organisms, the main water problem is drying out.
Temperature
Environmental temperature Is an important
abiotic factor because of its effect on metabolism.
http://www.wildherps.com/images/herps/standard/desert_iguana.jpg
http://www.sciam.com/media/inline/A186A7F7-D8EA-DDDF-0F715313A7DA2A91_1.jpg
Wind Some organisms depend on nutrients
blown to them by wind. Organisms such as plants depend on wind
to disperse pollen and seeds. Can also affect the pattern of a plant’s
growth.
http://www.asdk12.org/staff/vanarsdale_mark/pages/Ecology_Images/wind_tree.jpg
Rocks and Soil
Soil variation contributes to the patchiness we see in terrestrial landscapes.
In streams and rivers, the composition of the soil can affect water chemistry.
Periodic Disturbances
Catastrophic disturbances Can devastate biological communities.
After a disturbance, An area is recolonized by organisms, or repopulated by
survivors. The structure of the community undergoes a succession of
changes during the rebound.
Ecosystems
What biotic and abiotic factors do you see in this picture of the rain forest?
Ecosystems
What biotic and abiotic factors do you see in this picture of a tundra?
Populations• A population is…
Members of the same species… Who live in the same place At the same time.
Populations• The environment where a population
lives: habitat.
Populations Population ecologists study many
things about populations in their habitats:
Population size Population density Population growth
Population Density
Population density Is the number of individuals of a species per unit of area or
volume. In most cases, it is impractical or impossible to count all
individuals in a population. In some cases, population densities are estimated by indirect
indicators, such as number of bird nests or rodent burrows.
Populations Populations are densest where there
are resources available.
Populations
Patterns of Dispersion
The dispersion pattern of a population is the way individuals are spaced within the population’s geographic range.
Clumped Pattern of Dispersion
Individuals aggregate in patches.
Uniform Pattern of Dispersion
Results from interactions among the individuals of a population.
Random Pattern of Dispersion
Individuals are spaced in a patternless, unpredictable way.
Population Growth Models
Two models, the exponential growth model and the logistic growth model, will help us understand population growth.
The growth rate Is the change in population size per time
interval.
The Exponential Growth Model: The Ideal of an Unlimited Environment
The exponential growth model Describes the rate of expansion of a population
under ideal, unregulated conditions.
The Exponential Growth Model: The Ideal of an Unlimited Environment
• A key feature of the exponential growth model is that the rate at which a population grows depends on the number of individuals already in the population.
The Logistic Growth Model: The Reality of a Limited Environment
In nature, a population may grow exponentially for a while, but eventually one or more environmental factors will limit its growth.
Population-limiting factors restrict population growth.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The Logistic Growth Model: The Reality of a Limited Environment
The logistic growth model Describes growth of an idealized population that is
slowed by limiting factors.
A comparison of the logistic growth model and the exponential growth model
Carrying Capacity
Is the number of individuals in a population that the environment can just maintain with no net increase or decrease.
http://www.abc.net.au/reslib/200710/r189329_709751.jpg
Regulation of Population Growth Density-Dependent Factors
Are population-limiting factors whose effects intensify as the population increases in size.
Increase a population’s death rate and decrease the birth rate.
Regulation of Population Growth Density-independent factors
Are population-limiting factors whose intensity is unrelated to population density.
Include events such as seasonal freezing. In many natural populations, density-independent factors limit
population size before density-dependent factors become important.
Growth Rate Four influences:
Birth rate Death rate Immigration Emigration
Birth + Immigration – Death – Emigration
Population Cycles
Some populations Have regular boom-
and-bust cycles. Boom-and-bust
cycles of the snowshoe hare and one of its predators, the lynx
Communities and Ecosystems
Ch. 19
Key Properties of Communities
Diversity—variety of different kinds of organisms that make it up
Prevalent form of vegetation—determines kinds of organisms that will survive in the area
Stability—ability to resist change and return to its original species composition after being disturbed
Trophic level—feeding relationships among the various species
Diversity
The diversity of a community Is the variety of different
kinds of organisms that make up the community.
Species richness, the total number of different species in the community
Relative abundance of the different species
Which community is more diverse?
Interactions Between Populations of Different Species Interspecific interactions—occur b/w
populations of different species Coevolution—a change in one species
acts as a selective force on another species
Interspecific Competition
Competition occurs when 2 or more populations overlap in their niches Limiting resources
Food Space Mates
Generally, one will out-compete the other
Competition in Nature Two possible Outcomes
1. Weaker competitor becomes extinct
2. One or both species may evolve enough to use a different set of resources (resource partitioning)
Competition cannot operate for long periods of time
Competitive Exclusion Principle Two species cannot
coexist in a community if their niches are identical
Joseph H. Connell Study
Interactions Between Populations of Different Species Predation—consumption of
one organism by another Parasitism—specialized
predator (parasite) lives on/in its host, not killed immediately
Endoparasitism—live inside host (tapeworms/viruses)
Ectoparasitism—live on surface
of host (mosquitoes/aphids)
Herbivory—herbivores consume plants
http://www.dl-digital.com/images/z_oldimages/2002-10-d28-aphid2-fr18.jpg
Predator Adaptations Most predators have acute senses. Many predators
Have adaptations such as claws, teeth, fangs, stingers, or poison to help catch and subdue prey.
Are fast and agile.
http://upload.wikimedia.org/wikipedia/commons/thumb/7/7c/Hawk_eating_prey.jpg/300px-Hawk_eating_prey.jpg
http://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/00123/00123ed3.jpg
Plant Defenses Against Hebivores Physical defenses
thorns, hooks/spines on leaves
Chemical defenses Make plant
distasteful or poisonous
Morphine from opium poppy
Nicotine from tobacco
www.treklen
s.co
m/.../Swed
en/
photo19
8584.htm
Poison Ivy
http
://e
n.w
ikip
edia
.org
/wik
i/Im
age:
Tox
icod
endr
on_r
adic
ans.
jpg
Animal Defenses Against Predators Behavioral defenses
Alarm cries Distraction displays
Cryptic coloration/shape (camouflage)
Blend in with environment Asposematic coloration
Red/black; yellow/black
Mechanical/chemical defenses Quills, spines, and other
similar structures Toxins—distasteful or
poisonous
www.las
pilitas.com/.../
Monarch
_butterfly.htm
Monarch butterfly on Milkweed
http
://im
ages
.wild
mad
agas
car.
org/
pict
ures
/isal
o/w
alki
ng_s
tick0
071.
jpg
Stick Insect
Animal Defenses Against Predators
Mimicry—prey resembles species that cannot be eaten Batesian mimicry: Imitate
color patterns or appearance of more dangerous/unpalatable organisms
Müllerian mimicry: 2 unpalatable species that inhabit the same community mimic each other
Animal Defenses Against Predators Mimicry can be used to lure
prey Snapping turtle wriggles
tongue like a worm to attract and capture small fish
Angler Fish attract prey close enough to their mouths to be easily grabbed
http://ww
w.lancashirem
cs.org.uk/gallery/pics/lophius.jpg
Symbiotic Relationships
Non-Beneficial Parasitism—host harmed
Beneficial Mutualism—both partners benefit
Lichens-association b/w fungus and algae Nitrogen-fixing bacteria and legumes
Community Structure
Predators can moderate competition among its prey species
Keystone species can alter the whole community
Community Structure
Introduction of a species (exotic species) into a community can have drastic affects on the existing community members
Lake Davis, CA
http://www.dfg.ca.gov/lakedavis/
Northern Pike
http://aquanauts_dc.homestead.com/files/northern_pike1.jpg
Disturbances in a Community Storms, fire, floods, droughts, overgrazing,
or detrimental human activities: Remove organisms Alter resource availability
Create opportunities for new species that have not previously occupied the habitat
Humans are the biggest disturbance Logging, agriculture, overgrazing
Ecological Succession Primary succession
Begins in a virtually lifeless area where soil has not formed
Lichens and mosses colonize first Soil gradually forms and small plants and shrubs take
root
Secondary succession Occurs where an existing community has been cleared
by some disturbance that leaves soil in tact Earliest plants to recolonize are often those that grow
from wind-blown or animal-borne seeds
Ecological Succession
Tolerance to abiotic conditions determines early species
Competition among early species shape the succession of an area
Mt. St. Helen 1980 Eruption
http://denali.gsfc.nasa.gov/research/volc2/MSHreflection.gifMSH80_st_helens_spirit_lake_before_may_18_1980.jpg
http://www.jqjacobs.net/photos/volcano/st_helens.html
Mt. St. Helen Secondary Succession
Red alder disperses easily and is capable of rapid growth on the nutrient-poor, volcanic deposits.
A red-legged frog –one of the creatures living in one of the dozens of ponds created after the eruption.
70 species of birds, including hummingbirds, western meadowlarks and Savannah sparrows
http://www.kgw.com/news-local/stories/L_IMAGE.101688cd0b5.93.88.fa.7c.27913b573.jpg
www.kgw.com/news-local/stories/kgw_051505_env...
www.kgw.com/news-local/stories/kgw_051505_env...
An Overview of Ecosystem Dynamics
An ecosystem Is a biological community and the abiotic
factors with which the community interacts.– Energy flow
• Is the passage of energy through the components of the ecosystem.
– Chemical cycling• Is the use and reuse of chemical elements within
the ecosystem.
Energy
Flows through an ecosystem when consumers feed on producers.
Cannot be recycled within an ecosystem, but must flow through continuously.
Ecosystem Dynamics
Energy flow and chemical cycling Depend on the transfer of substances in the
feeding relationships, or trophic structure, of an ecosystem.
Trophic relationships Determine an ecosystem’s routes of energy flow
and chemical cycling.
Trophic levels Divide the species of an ecosystem based on
their main sources of nutrition.
Trophic Relationships Ecosystems divided into trophic levels
(feeding levels) Producers—autotrophs (mostly photosynthetic) Primary consumers—herbivores Secondary consumers—carnivores that eat
herbivores Tertiary consumers—carnivores that eat other
carnivores Detrivores—consumers that eat dead or
decaying matter
Food Chain/Food Web
Energy Flow in Ecosystems
Each level in a food web contains a different quantity of stored chemical energy
When consumers eat producers or 2 consumers eat 1 consumers, some energy is lost in each transfer from one level to the next
Energy pyramid
A diagram that represents the cumulative loss of energy from a food chain.
Chemical Cycling in Ecosystems Ecosystems
Depend on a recycling of chemical elements.
Biogeochemical cycles Are chemical cycles in an ecosystem that
involve both biotic and abiotic components.
Biogeochemical Cycles
Three key points : Each circuit has an
abiotic reservoir. A portion of chemical
cycling can rely completely on geological processes.
Some chemicals require processing before they are available as inorganic nutrients.
Examples of Biogeochemical Cycles
Carbon Nitrogen Phosphorus Water
Carbon Cycle
Human Impacts: Greenhouse Effect
Increase of atmospheric CO2
Combustion of fossil fuels
Burning of wood from deforestation
Increase in global temperature
Nitrogen CycleHuman Impact: Cultivation—turns up soil and ↑
decomposition of organic matter; Releases more nitrogen Harvesting ↓ nitrogen from
ecosystem Adding industrially
synthesized fertilizers to soil has resulted in doubling globe’s supply
Excess nitrogen leeches into soil and into rivers, streams, and lakes and ground water—
– ↑ levels are toxic to aquatic organisms and humans
– Algal blooms in lakes ↑ eutrophication
Phosphorus Cycle
Human Impact: Sewage treatment
facilities and fertilizers ↑ amounts of
phosphates to aquatic systems, causing eutrophication of lakes.
Water Cycle
Human Impact: Destruction of tropical
rain forest Will change the amount
of water vapor in the air. May alter local and global
weather patterns. To irrigate crops,
humans pump large amounts of ground water to the surface.