ES 10
Lecture key points and notes: Ecology and ecosystems
Some basics:
Life:
 Organized internal structure
 DNA
 Capture energy from their environment
 maintain internal conditions seperate from external
 arise through reproduction
 can adapt through mutations and adaptations
Life on Earth depends on:
One way flow of high quality energy (high to low)
Cycling of matter
Gravity
Basic unit of life is the cell:
1)Eukaryotic (higher orgs-nucleus)
2)Prokaryotic (bacteria, no nuc, small)
Differences
CELLS:
Prokaryotic
Bacteria
DNA folded into
nucleic area
Small
no membrane bound organelles
Thick cell wall
RNA
Eukaryotic
Higher organisms
Nucleus w/DNA
Organelles
Larger
Taxonomy: Domains, kingdoms and Lineaus(a person): KPCOFGS. Know the
general order with which we classify organisms.
Classification of life
Domains: Bacteria, Archaea, Eukarya
Kingdoms (5 major ones)
Bacteria (eg. decomposers, many are pathogens)
Protista (Eukaryotes, single celled) phyto plankton, diatoms. NOT monophyletic
Fungi Eukaryotes: molds, mushrooms, yeasts
Plants photosynthesize
Animals respire
Herbivores, carnivores, omnivores
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Vertebrates, invertebrates
Phylum
Class
Order
Family
Genus
Species
Example humans:
Animalia
Chordata
Mammalia
Primates
Hominidae
Homo
Sapiens
Things are classified by relatedness and similarities
Ecology
Study of interactions between living things (eg. Competition, predation…) and their nonliving environments (eg. Chemistry of the soil, sunlight, temperature etc)
A study of the distribution (eg. Random, systematic, clumped) and abundance of living
things. Distribution depends on the availability of resources, and interactions with living
and nonliving things.
Primary productivity: rate of biomass production (plant) means amount of plant
material produced over a certain time (eg. One year). Depends on light, nutrients,
temperature, moisture (rainfall). Determines major Biomes, which are described by their
vegetation (we’ll get to these later). The amount of primary productivity also affects
populations.
Complexity of ecosystems: food webs
‘Mature’ ecosystems are those which have had time to stabilize. Complex ecosystems
take longer (those with many species at each trophic level, and many niches.
Food webs in complex ecosystems are truly complex (see figures in your book)
Trophic levels: producers (plants), primary consumers (herbivores or plant eaters),
secondary consumers, tertiary consumers (predators).
Energy flow through trophic levels: energy is lost at each level. Primary producers use
energy directly from the sun, while higher level consumers rely on energy already
processed, making them overall less efficient.
Food pyrimid: 80-95% loss of energy w/ every level
2nd law of Energy (high to lower state---heat). Better to feed lower on the
pyrimid!!
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No waste! (decomposers)
Who eats who?
Toxin buildup how it happens (clams,fish etc._, and finally to a top order predator (like
us) who end up eating animals who have concentrated the toxin to high levels:
Biomagnification
Natural selection – A theory ‘discovered’ by Charles Darwin
Organisms are subject to the forces of evolution and natural selection which lead to
adaptations, and eventually occupation of a specific niche.
Adaptation and natural selection is the result of survival and reproductive success over
many generations (usually). Traits that are not selected for (or are selected against), are
weeded out of the gene pool. So…for example, if environmental conditions are such that
members of a species who have excess fat (say a marine mammal) tend to get too hot and
may not hunt as well, their offspring will not be as successful (to grow up and breed
themselves). Over time, this trait will be weeded out of the population, and those with
less fat will have more offspring. Thus the species will adapt over time and have less fat.
This process could also progress in the reverse (selecting for fat).
Niche: The ‘role’ or ‘house’ or ‘what an organism does’. This includes what they eat,
where they eat it, how they eat it, etc. **No two species can occupy the same niche.
Problems with introduced species – they often take over existing niches, outcompeting
native species. Competitive exclusion principle (resource partitioning, competitive
exclusion).
Specialists, generalists, opportunistic, pioneer
Species and speciation: Natural selection, competition, differential success, geography,
hybridization can all lead to speciation.
Tolerance limits:
Organisms have tolerance limits – usually to abiotic factors such as temperature, rainfall,
soil chemistry, salinity (such as in the ocean) etc.
This just means that there is an optimal (best) range of (for example) temperature. Below
of above that level, the organisms don’t do so well. Many organisms react to critical
levels of tolerance. That is, they will slowly decline in numbers until the factor reaches
some critical level, and then there will be a sharp decline in populations (this is often true
of tolerance to chemicals and toxins).
Limiting factor: too much or too little of an abiotic factor can limit or prevent growth
even though all other factors are within tolerance range.
(terrestrial): temp, water, light, nutrients (phosphorous!),
(aquatic) salinity, temp
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Abiotic/Biotic
ABIOTIC (physical and chemical factors)
PHYSICAL
Sunlight
Temperature range
Rainfall
Wind
Latitude
Altitude
Fire frequency
Soil type
Water currents
Particulate matter (water)
Water level
CHEMICAL
Nutrients
Toxins
Salinity
Dissolved O2
BIOTIC (Living organisms) – Species Interactions
These include interactions between organisms, and the impact that has on the ecosystem
Competition – for a limited resource.
Intra specific – within a species
Inter specific – between two species
Competitive exclusion – when one wins, and one is outcompeted and either
dies off or migrates away.
Resource partitioning – sharing a resource – eg. The vultures where the
different species feed off different parts of the carcass.
Predation
Carnivore/herbivore/omnivore. All are predators. Grazing would be included here, but
not scavenging (eating dead things). Predators often have a profound effect on an
ecosystem(eg mountain lions, deer, and plant communities are all in ‘balance’).
Symbiosis: organisms that live in close association
Key point: the symbiont and host co-evolve together. Often these relationships are very
specific, and in the case of some, they cannot live without each other. For example we
have a bacteria (a friendly one) that lives inside of us and helps us process our food. It
needs us and we need it. An example of dependant mutualism.
Mutualism: both benefit (birds that pick ticks off the backs of rhinos and cattle,
or sea anemones and clown fish)
Parasitism– One benefits, one is put at a disadvantage (eg ticks and dogs)
Commensalism: one benefits and one is not affected. I question whether one is
truly not affected though…An example would be the cattle egrets that feed
by the feet of cattle who are grazing. The grazing cattle kick up bugs that
the egrets eat. Good for the egrets, probably doesn’t affect the cattle
much.
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Defense and/or competitive advantage (eating):
Organisms use a variety of strategies to avoid being eaten or to eat better. These include:
toxins, body shape/armor, speed, color (can be used to camouflage or to advertise toxicity
and reproductive state), spines. Mimicry – steel someone else’s colors and look toxic.
Keystone species: a species that has a particularly strong influence on community
structure. The Sea otter/kelp bed example. Kelp itself. ‘Minor’ species can also have
important roles though…
The sea otter/kelp killer whale story: The Aleutian Island studies
Sea Urchins eat kelp, especially new recruits
If kept in check, they eat drift kelp
If populations expand, they will eat established kelp
Sea Otters eat urchins, especially exposed ones
They will keep sea urchin populations in check
Killer whales feed on steller sea lions which feed on Pollack, a type of fish. Humans are
overfishing Pollack, which leaves the sea lions with no food. The then hungry killer
whales have turned to sea otters, eating them off in large numbers. With no sea otters,
urchins have multiplied and are eating all the kelp. That whole ecosystem has now
changed, and kelp beds no longer exist in areas where they were once extensive.
Wolves in Yellowstone: results of reintroduction
The reintroduction of wolves in Yellowstone National Park has led to a rebuilding of the
ecological communities. By driving the Elk back up into the hills, the wolves have
‘allowed for’ the riparian trees to come back, which has led to the return of songbirds,
increased seed dispersal, etc.
Populations…
population dynamics
speciation (what is a species?)-new species develop due to several major driving forces:
1) isolation of populations is an important one. Some barrier develops (such as a
climactic barrier, physical such as a mountain range, currents in the ocean etc) which
isolates a population. That population adapts to its environment and can become a
new species.
2) Another way is species radiation into new niches. Galapagos finches did this-new
species developed as a result of niches (such as feeding on different food sources),
which allowed new species to develop and adapt to those niches.
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Endemic species are those found only in a particular area, and nowhere else. Islands
often have endemic species, and so are important in preserving and understanding
biodiversity and adaptation.
Factors affecting populations:
Death rate, birth rate, infant mortality, density, age distribution, distribution in space,
resources, limiting factors, tolerance limits, biotic and abiotic interactions, male to female
ratio.
The balance between birth rate, death rate and infant mortality (death in babies) is
important in determining population growth rates. Age distribution (eg. The number of
young or old members of a population) is also important. Lots of young in a population
represents a high potential for population growth (as the young reach reproductive
maturity). Conversely, if there are few young and many old members of a population, the
population growth rate will be low. Density can have an important effect too (eg. With
rabbits where too many causes females to become infertile, or even kill their young).
Exponential population growth (multiplicative – also known as J-curve). Potential for
growth if nothing were limiting expansion. As opposed to additive or slow growth. Most
populations experiencing exponential growth will feel increasing pressure from
environmental factors (those things listed above that affect population growth) and the
rate will slow. Eventually a limiting factor will cause the population growth to stabilize
around the carrying capacity.
Carrying capacity: most ecosystems have a limit to the number of any one species that
can live there due to limits in food items, nutrients etc. Boom and bust represent an
ossilation around the carrying capacity (usually). Some are regular and seasonal, others
are episodic and rare (like locusts). The ossilation will generally stabilize a bit over time,
but will always vary a little just above and/or below the carrying capacity.
Stable population growth is the result of equilibrium between a species’ growth and
environmental factors. In many cases a limiting factor will be responsible for this
Limiting factor: too much or too little of an abiotic or biotic (usually abiotic) factor can
limit or prevent growth even though all other factors are within tolerance range.
(terrestrial): temp, water, light, nutrients (phosphorous!),
(aquatic) salinity, temp
Other limiting factors include things like food and water availability, habitat
availability, or any other thing that might limit a population’s ability to grow.
K vrs. r adapted species (K= slow growth, long life, reproduce late in life, few offspring,
lots of parental care) r(r = short life, fast growth, lots of offspring, little parental care)
adapted species.
These reproductive strategies are important in determining a species’ susceptibility to
things like hunting/fishing pressure, and become important in management decisions. K
selected species are very susceptible to overhunting or other factors that lead to
population decline and are more prone to extinction (an extreme example are orangutans
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(an ape) which have one baby every 8 years or so!). r-selected species have a shorter
generation time, can usually recover more quickly, and often evolve more quickly. An
extreme example are many bacteria which have very short generation times, and within
the course of a few days can reproduce and adapt a resistance to antibiotics – a growing
problem in human health and disease control. Many animals can use a combination of
these though – ie. Rockfish which are long lived, reproduce late in life but produce of
offspring into which they put very little parental care.
Community disturbance: will an ecosystem always return to its same state after a major
disturbance? Why or why not?
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