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Chapter 42
Organisms in Their Environment
42.1 Ecological Systems Vary in
Space and over Time
• Physical geography-the study of the
distributions of Earth’s climates and
surface features
• Biogeography-the study of the
distributions of organisms
Ecological systems comprise organisms
plus their external environments
• Abiotic components (non living):
–Temperature, light, water, wind (together
= climate, prevailing weather conditions at
a certain location)
•Biotic components (living):
–Living organisms
•Ecological system –one or more
organisms plus the external environment
Abiotic vs biotic
http://www.sciencebitz.com/wp-content/uploads/2007/06/biotic-abiotic.gif
Ecology
• The study of the interactions of organisms
with other organisms and with the physical
environment.
• Studies life on many different levels—from
individual organisms to the biosphere.
Ecological systems can be small
or large
• Population—all the organisms within an area that belong
to the same species.
• Community—all the various populations that interact in a
particular locale, e.g. a coral reef, a forest, a pond, or even
a rotten log.
• Landscapes—multiple communities
• Ecosystem—a community of populations along with the
abiotic environment
• Biosphere—the zones of the earth’s soil, water, and air
where living organisms are found.
http://buffonescience9.wikispaces.com/file/view/ecological_levels.jpg/216935720/ecological_levels.jpg
• Large ecological systems tend to be more
complex (more parts)
• Small systems are still complex, (think of
your gut)
http://uwarboretum.org/images/eps/charact.jpg
Each ecological system at each
time is potentially unique
• Ecological systems depend on their
components (abiotic and biotic)
• They are different in each ecosystem and
change over time
• This means each system, at any given
time is unique (think of an example for
this)
The gut again
http://soreyfitness.com/wp-content/uploads/2013/01/intestines.jpg
Chapter 43
Populations
Population density and populations size
are two measures of abundance
• Population density: the number of individuals
per unit of area (for terrestrial organisms) or
volume (for organisms that live in air, soil, or
water)
• Population size: the total number of individuals
in the population
• Usually measure density and then multiply it by
the area occupied to calculate size
Density and size
http://www.drroyspencer.com/wp-content/uploads/ISH-trends-vs-population-density-regional-US.png
Chapters 44, 45, and 46
http://4.bp.blogspot.com/-ih4NN71hqIA/T5Ov-l2Ly_I/AAAAAAAACmc/iMDaqjb_oBs/s1600/Green%2BEarth%2BEcology%2BwAl%2Btangledwing.png
Behavioral ecology: science based on the
expectation that animals increase their Darwinian
fitness via optimal behaviors
For example, you might ask: why do some bird have so many songs
in their repertoire?
Behavioral Biology
• Ethology: study of how animals behave
Behavioral Biology
• Behaviors have genetic (nature) and
environmental (nurture) influences
• Innate behaviors: developmentally fixed
• Fixed action pattern: sequence of
unlearned behavioral acts that is
essentially unchangeable and usually
carried to completion once begun,
triggered by a sign stimulus (which is often
another species) Video
Sign stimulus
experiment: figure
out what is causing
one male fish to
attack another male
“fish” (fakes) video
male stickleback fish
attack other male
stickleback fish-- in
response to the red
sign stimulus (they
don’t attack females,
which do not have
red bellies, and they
do not attack “fake”
fish with no red on
the belly)
Response to
question about
the behavior
(cause/effect,
how, etc.)
Response to
evolutionary
significance of
the behavior
Imprinting– both learned and innate, usually not reversible,
has a sensitive or critical period video
Directed
Movements:
Kinesis: change
in activity or
rate in
response to a
stimulus– the
pillbug is more
active in dry
areas, less
active in moist
areas
Taxis:
movement
toward or away
from a stimulus;
can be positive
or negative
Pillbug video: pillbugs are isopods (crustaceans)
that are adapted to life on land (we call them “sow
bugs” or “roly-polies”—a common experiment is to
use choice chambers
Learning: an experience-based
modification of behaviors
• Even most innate behaviors improve with
performance and practice
• Habituation: loss of responsiveness to
stimuli that contain little or no information
– Why would this increase fitness?
–Allow animals’ nervous systems to focus on
stimuli that signal food, or danger, or mates
rather than wasting its energy
Experiment on the
nest-locating
behaviors of
digger wasps
(spatial learning)
Video
• Associative learning: associating one
stimulus to another
– Classical conditioning: associating an
arbitrary stimulus with a reward or punishment
(generally involuntary responses)
•Pavlov’s dogs (bell ringing resulted in salivation)
•video
–Operant conditioning: trial-and-error
learning, or repeating or avoiding a
behavior depending on if it resulted in
reward or punishment (generally voluntary
actions)
•Skinner’s rats manipulating lever to get food;
also important in predator-prey relationships
•video
Mating Systems
• Promiscuous: no pair bonding
• Monogamous: one male, one female
• Polygamous: one individual of one sex
mates with many of the other sex
– Polygyny: one male and many females
– Polyandry: one female and many males
Social Behaviors
• Agonistic behavior: contest involving both
threatening and submissive behaviors to
determine which competitor gains access
to a resource, often involves
•Ritual: symbolic activity (no one is actually
harmed—dogs bearing teeth or tucking tail
between legs) and results in
•Dominance hierarchy– the “pecking order”
Altruistic Behaviors
• Altruism: behaving in a way that reduces ones
own fitness but increases the fitness of the
recipient of the behavior (like an animal “on
watch” who vocalizes a warning to others)
• Video
•Inclusive fitness: the effect an individual has on
proliferating its genes by producing its own
offspring AND helping its close relatives increase
their production of offspring
–Measured in the coefficient of relatedness:
siblings= 0.5, cousins = 0.125; kin selection indicates
you’d choose to aid the sibling before the cousin
Population Ecology
• Two measurable characteristics of a
population:
• Density: # of individuals per area or
volume, and
• Dispersion: the pattern of the spacing of
those individuals
– Clumped: aggregation in patches
– Uniform: evenly spaced
– Random: umm…it is…random
• Demography: study of statistics that affect population
size
For example,
Age
structure:
number of
individuals at
each age at
a point in
time
– Birth rate/ fecundity
– Death rate
– Generation time: average time between birth
of an individual and the birth of their offspring
– Sex ratio: proportion of individuals of each sex
• Life table: predicts how long an individual of a
given age can be expected to live, may be
depicted as a
• Survivorship curve: shows the number of
individuals still alive at each age
• Also important to consider are:
– Number of reproductive episodes per lifetime
(semelparity: one “big” one or
iteroparity: lots of “smaller” ones)
– Number of offspring per episode (fecundity)
– Age at first reproduction
Pacific salmon
Grain (annual plants)
Population growth models
•Exponential model: an idealized population in an unlimited environment
J-shaped curve (boom and bust)
• Logistic growth: incorporates the idea of
carrying capacity (K), the maximum
population size an environment can really
support
• As N approaches K, the rate of growth (r)
slows
• When N=K, then r=0, resulting in Zero
Population Growth
Limiting Factors affect carrying
capacity
• Density Independent Factors: weather
and other natural disasters
• Dependent Factors: food, space, water,
parasitism, competition
• Two different strategies:
– K-selected populations tend to live at or near
carrying capacity (K) (long life, few offspring
but multiple episodes, extensive parental
investment)
–r-selected populations tend to fluctuate a lot
and be opportunistic (short life, lots of offspring
per few reproductive episodes, limited parental
investment)
r-strategist
K-strategist
Family characteristics
Large litter size
Small litter size
Short birth spacing
Long birth spacing
Many offspring
Few offspring
High infant
mortality
Low infant mortality
Little parental care
Much parental care
r-strategist
K-strategist
Individual characteristics
Rapid maturation
Slow maturation
Early sexual
reproduction
Delayed sexual
reproduction
Short life
Long life
High reproductive Low reproductive
effort
effort
High energy
utilization
Efficient energy
utilization
Low
encephalization
High
encephalization
r-strategist
K-strategist
Population characteristics
Opportunistic
exploiters
Consistent exploiters
Dispersing
colonizers
Stable occupiers
Variable
population size
Stable population
size
Lax competition
Keen competition
Social system characteristics
Low social
organization
High social
organization
Low altruism
High altruism
Community Ecology
Video: Secret Life of Plankton
•Interspecific interactions
(between different species)
•Predation (+/-)(predator eats
prey)
•Parasitism (+/-) (needs a
host)
•Herbivory (+/-) (animal eats
plant)
•Commensalism (+/0)
•Mutualism (+/+)
Competition
• Competitive exclusion: when populations of two
similar species compete for the same resources,
one will be more efficient, leading to the demise
of the other
• Ecological niche: the total of a species’ use of
the biotic and abiotic resources in its
environment (two species cannot coexist in one
environment if their niches are identical)
Animal defenses against predators
• Cryptic coloration (camouflage)
• Aposematic coloration (warning coloration)
• Mimicry (resembling another species)
– Batesian mimicry: harmless species mimics a harmful one
– Mullerian mimicry: two or more unpalatable species resemble
each other
Community development
• Ecological Succession - involves a series of
species replacements
• Primary Succession - occurs where there is no
soil formation (volcanic island)
• Secondary Succession - occurs after an area
is disturbed (prairie fire)
• Pioneer Species - first species to inhabit an
area
Climax Community - when the species
replacement slows and the ecosystem stabilizes
Community Biodiversity
• Intermediate Disturbance Hypothesis - moderate
disturbances in an ecosystem are necessary to maintain
biodiversity
• Keystone Species - needed to maintain biodiversity
(often top predators)
– Ex: Kelp, Sea otters, Sea urchins, Abalone - what happens when
you remove the otters
• Exotic Species - a species introduced into a habitat,
often causes major disturbance and even extinction of
native species
– Ex: Kudzu, Snakehead catfish, Piranha, Mussels
Invasive species Video
Ecosystems
• Trophic levels: feeding relationships within
an ecosystem
– Primary producers/autotrophs
– Primary consumers/herbivores
– Secondary consumers/carnivores
– Tertiary consumers, etc.
Figure 54.1 An overview of ecosystem dynamics
• Ecological
efficiency:
amount of
energy
transferred
from trophic
level to
trophic level
(usually
about 10%),
shown as a
biomass
pyramid
Energy Flow
• Food web—represents the various
interconnecting paths of energy flow in an
ecosystem.
– Grazing food web—begins with a producer
grass  zebra  lion
--detrital food web—begins with detritus
detritus  earthworm  shrew
Trophic Levels
• Trophic refers to feeding.
• Trophic levels can be linked in a line called
a food chain.
• Trophic level—composed of all the
organisms that feed at a particular link in a
food chain.
leaves  caterpillar  bird  hawk
Figure 53.10 Examples of terrestrial and marine food chains
Figure 53.11 An Antarctic marine food web
Figure 54.14 Food energy available to the human population at different trophic
levels
Ecological Pyramids
• Only about 10% of the energy of a trophic
level is available to the next trophic level.
• Can be depicted as an ecological pyramid
or pyramid of energy.
• Can also have pyramids of numbers (there
can be a problem with one large producer
such as a tree supporting many herbivores
such as caterpillars).
• Pyramids of biomass eliminate size as a
factor because biomass is equal to the
number of organisms multiplied by their
weight.
Figure 54.10 Energy partitioning within a link of the food chain
Biogeochemical Cycles
• Named because chemicals circulate through
both living and nonliving components of an
ecosystem.
Figure 54.16 The water cycle
Figure 54.17 The carbon cycle
Figure 54.18 The nitrogen cycle
Figure 54.19 The phosphorous cycle
Biological Magnification
• Nonbiodegradable materials such as heavy
metals and pesticides are not degraded
under normal conditions (by decomposers) or
in sewage treatment plants).
• As they pass along the food chain, they
become more and more concentrated
because they remain in the body and are not
excreted.
• Human milk contains detectable amounts of
DDT and PCBs which are organochlorides.
Figure 54.24 We’ve changed our tune
Biological magnification: substances become more
concentrated with each link in the food chain