Introduction to
Ecology
Reading: Freeman, Chapter 50.
Ecology is the scientific study
of the distribution and
abundance of organisms, and
their interactions with the
environment.

The word “ecology” comes from the
Greek words “oikos”, meaning house,
and “logos”, to study.
What do we mean by
“scientific study”?



There are hundreds of different sciences;
each employs different techniques and has
its own methods and standards of evidence.
In one form or another, the “scientific study”
of every subject uses the hypotheticodeductive approach.
This approach is rather new historically,
tracing its roots back to the European
enlightenment of the sixteenth and
seventeenth centuries.
Essentially, it goes something like this



 A scientist, or group of scientists, becomes
interested in explaining one aspect of how
the natural world works. (This comes easily
for scientists, as well as most people,
people are curious...)
 Both intentionally and unintentionally,
scientists conduct observations. (Some
observations may be commonsense or
centuries old (i.e., the tides), others may
require specialized experience (variation in
scutellar hair number on different strains of
Drosophila)
A hypothesis is constructed based on all
the pertinent observations.
A hypothesis is a suggested
explanation for a phenomena, based
upon a conceptual “working model”
of how a system works.
 Good hypotheses generate predictions that
can be tested.
 In experimental sciences, experiments are
set up to test the hypothesis.
– In the historical sciences, additional evidence is
gathered in the place of experiments (although
not nearly as incisive, some areas do not easily
lend themselves to experiments (i.e., stellar
astronomy)).

If the predictions of the hypothesis are not
borne out, the hypothesis is falsified.
 Interestingly, a hypothesis cannot
be proven true by an experiment,
even when it correctly predicts the
outcome.



This is because an infinite number of
hypotheses can usually be generated that
predict the same outcome.
The strongest hypotheses are usually
accepted as true if multiple experiments fail
to falsify them.
These hypotheses, and their underlying
models, form scientific paradigms which
may last for centuries or longer. Scientific
paradigms are explanations for how the
world works, they inspire future research,
but also limit its direction to certain avenues.
Example-Zonosemata wing
markings.
Observation-Zonosemata flies have
dark bands on their wings. They
wave them up and down when
disturbed.
 Based on the prevailing scientific
paradigm in biology (Darwinism)-Erick
Greene asked “How could the
behavior evolve by natural selection?”

3 hypotheses



Hypothesis 1-Wing patterns and displays
evolved by sexual selection. (courtship
displays such as this are common in flies)
Hypothesis 2-Wing patterns and displays
evolved to scare predators by “mimicking” a
jumping spider. (mimicry is a common
defense in the animal kingdom)
Hypothesis 3-Displays evolved to deter
predation by jumping spiders themselves.
Experiment








He created five experimental groups
1-Untreated controls
2-Zonosemata with own wings re-glued
3-Zonosemata with housefly wings
4-Houseflies with Zonosemata wings
5-Untreated houselfies
He subjected flies from each treatment to
starved jumping spiders and other
predators, conducted 20 trials, measured
number of times spider or other predator
attacks v.s. retreats.
Questions-Why group 2? Why not just 1
trial?
Predictions
Hypothesis 1-All flies should be
attacked.
 Hypothesis 2-Jumping spiders should
attack all groups. Other predators
should attack groups 3-5, but leave 1
and 2 alone.
 Hypothesis 3-Other predators will
attack all groups. Jumping spiders will
avoid groups 1 and 2 but attack
everything else.

What does this data
suggest?
# of kills out of 20 trials

Jumping spider
Anole
 Group 1
4
19
 Group 2
4
20
 Group 3
20
19
 Group 4
20
20
 Group 5
20
19

Ecology has a long history as a
historical science, and is becoming
an experimental science.
At the moment, ecology lacks a
scientific paradigm because many of
its underlying ideas have not been
sufficiently tested or have crumbled
under the weight of new experiments.
 This makes ecology an exciting field,
because new discoveries can have an
enormous impact

Based Upon the Questions
they Choose to Ask,
Ecologists May Work at One
or More of Several Different
Levels of Organization:
 Individuals
 Populations
 Communities
 Ecosystems
Individuals are single, discrete
organisms.


...In some cases, it is easy to define an
individual organism, i.e., mice and people.
In other cases, the distinction between
individuals is arbitrary or nonexistent. A
stand of aspen trees looks like many
individuals above the ground, but below
ground they are all interconnected. A single
fungus mycellium may occupy tens of
square kilometers beneath the surface of a
forest.

For example, a scientist might ask a
question about how a cave cricket finds its
way in and out of the entrance of a cave
every time it forages. This is called
organismal ecology.
Populations are groups of organisms
of the same species living in the
same place.
Individuals of the same population
interact with one another: most
interaction among members of a given
species occurs within a population
 They may compete for resources and
mates, they may combine alleles via
sexual reproduction.

Examples of
populations include:
...a herd of wildabeast
 ...all the bullhead catfish living in a
midwestern lake
 …all of the tropicbirds nesting on a
single oceanic island
 ….the E. coli population in a single
person’s gut


Population ecologists ask questions at
this level. Very frequently, these questions
concern abundance, density, population
growth, and limits to growth. For instance, a
population ecologist might study the extent
to which the number of available nest sites
affects the maximum number of tropicbirds
an island can sustain.
Communities are assemblages of
populations of different species
living in the same place

Different species have different
“functions” in a biological community.
– For instance, some are decomposers,
some are producers, etc.
– Some species within the community may
interact to a great extent, while interaction
between other species may be virtually
nonexistent.
 The
extent to which biological communities
are tightly knit systems, or opportunistic
assemblages, is debated.

A community ecologist might ask
questions about the extent to which
parasitic wasps control outbreaks of
pine sawflies, and whether the
presence of parasitoids is necessary
for the presence of pine trees.
www.hort.wisc.edu/.../insects/eps/eps.htm
Ecosystems

Ecosystems are interacting
assemblages of living things living in a
particular area, accounting also for the
nonliving components, such as light,
water, nutrients, soil, and seasonality,
that are important to life.
– Ecosystems are nested within other
ecosystems.

An ecosystems ecologist studying caves
might ask questions about the role of bat
guano entering the caves, and the extent
to which nutrients and energy brought in
by the bats from outside, via their guano,
support the nonphotosynthetic
ecosystem in the cave.
What is a Species?



The concept of a species is fundamental to
biology, yet biologists disagree on exactly
what constitutes a species.
There are several different, working
definitions of a “species”
Different branches of biology use different
working definitions because they have
access to different information or because of
fundamental differences in the biology of the
organism in question.
“Biological Species
Concept”
“A species is a group of actually or
potentially interbreeding organisms
that can mate and produce fertile
offspring” –Ernst Mayer
 This definition is very interesting from
an evolutionary perspective. It defines
species as “real”, objective entities,
defined by the limits of gene exchange

Morphological Species
Concept



“Species are Groups of Organisms that
Share Certain Morphological or Biochemical
Traits”
Some species do not reproduce sexually,
some are known only from fossils. This
definition is the working definition used by
biologists that cannot, or should not, use the
“Biological Species Concept”
It is more subjective
Phylogenetic Species
Concept

A species is a discrete lineage,
propagated, ancestor to descendent
through time, which is recognizably
different from other such lineages and
shares a distinct evolutionary history.
It defines a species by its relationship
to other species.
Example of an ecological
hypothesis test


Robert Marquis and Chris Whelan studied the role of birds
in limiting the density of herbivorous insects.
They observed that deciduous forests harbor hundreds of
species of herbivorous insects, yet only a small proportion
of total leaf area is eaten every year.
 Many species of birds are insectivores, but spiders,
parasitic wasps, and fungal infections also attack
insects. Are birds an important factor in controlling
herbivores?
 Experimental
Treatment-Multiple
trees (replication is important) are
enclosed in cages to exclude birds
but not insects.
 Control Treatments– ”Control trees” paired with the
excluded trees control for
environmental variation.
– Incomplete cages-control for the
presence of the cage.
 Data Collected– % of leaf area eaten
– density of herbivorous insects
 Prediction-if birds are an important
agent of insect control, both variables
should be higher in exclusion cages
Result
Caged trees had 70% more insects
than controls, and caged trees had an
increased percentage of missing leaf
area (35%) relative to control trees
(22%)
 Conclusion-birds are an important
potential agent of herbivore control.


Other studies– One of the most important attributes of a
good experiment is that its results be
reproducible.
– This is a problem in ecology, because
conditions in “the field” vary from year to
year and place to place-it is almost never
possible to reproduce a field experiment
exactly.
– Exclusion experiments of this type have
been done many times, with different
results
Ecological Time Scales
Ecological processes may occur over time scales ranging
from days to millennia.
The ecological time scale is shorter than the evolutionary
time scale, but there is some overlap-populations evolve over time,
and this can affect the composition of communities and functioning
of ecosystems.

What we see today might reflect events that
happened long ago by our standards.
– Example-colonization of North American forests
following glaciation-a continuing process
 Alpine
populations of tundra communities persist at high
elevations
 Chicago was under ice 15,000 years ago-“Lake Chicago”
existed here thereafter, gradually growing as the glacier
melted-it drained out the Mississippi.
– As a result, The community of Great Lakes fish species
resembles that of the Mississippi river, rather than the Atlantic
ocean.
 Deciduous
trees have replaced Pine and Juniper as
warm conditions persisted– Different species have colonized at different rates.
– A relict population of Pines is still present at Indiana Dunes
national Lakeshore.
Climate vs. Weather
Weather is the particular set of abiotic
conditions, such as rainfall, sunlight,
temperature, and humidity, affecting a
particular area at a particular time.
 Climate is the overall pattern of
weather in that area.
 Weather changes daily, climate
changes over decades, hundreds, or
thousands of years




Biomes are broad assemblages of plant
and animal communities generally defined
by the dominant vegetation.
This is an old concept in ecology, first
established by the terrestrial plant ecologists
F.E. Clements and V.E. Shelford.
Biomes paint a broad swath of an area
based upon what the dominant vegetation
looks like. A recent approach has been to
be more specific by naming Ecoregions.
Ecoregions are major ecosystems that
result from predictable patterns of climate as
influenced by latitude, global position, and
climate.
Terrestrial Biomes
(some scientists count them
differently)





Tundra
Taiga or Coniferous Forests
Desert
Chaparral
Grasslands
– Savannah


Temperate Deciduous Forests
Tropical Rain Forests
– Tropical Dry Forests
Terrestrial biomes have characteristic
vegetation determined by the amount
and timing of water, the amount of
available sunlight, and by temperature.
 Vegetation provides a spatial structure
to terrestrial biomes.
 Spatial structure creates microenvironments important to various
different organisms
 Biomes differ greatly in their
productivity and their biodiversity

Major Physical Factors
influencing terrestrial
biomes



Rainfall, and its timing
Sunlight
Disturbance
warm wet areas favor rainforests
Intermediate areas can
be either grassland or
forest, depending upon
other factors
Tundra receives very little precipitation, deserts range from hot to cold
Tundra
Tundra is characterized by the lack of
trees, the dominant vegetation is
lichens, annual grasses, and, in some
places, very specially adapted shrubs
and woody plants.
 Tundra occurs in polar climates and at
high elevations, where the growing
season is very short. Nearly all
precipitation falls as snow.
 Plants and insects flourish during the
short growing season.

Taiga or Coniferous Forest





Cone-bearing trees such as pine, spruce,
and fir dominate. most are dominated by
one or a few species
This biome is very common, covering huge
areas at high latitudes or high elevations
The cool to warm summers are the growing
season
Plants are dormant during the winter, when
temperatures drop far too low for
photosynthesis.
Often, much of the precipitation falls as
snow. Snow melt releases a great deal of
water into the communities that make up the
taiga
Desert






Low rainfall, generally less than 30cm per year,
characterizes a desert
Many deserts are very hot (at least during the
day), but some, such as the Great Basin and the
Gobi Desert, are cold most of the year.
The dry environment often causes a dramatic
difference in temperature between day and night
Grasses are usually found when water is available
(they are dormant underground, or as seeds,
when there is no water).
Succulents, such as cacti and euphorbs, and
shrubs with specialized water-saving adaptations,
are present.
Trees are uncommon or totally absent.
Chaparral:






Cool, rainy winters and dry summers
Dense, spiny, evergreen shrubs dominate
Seasonal fires
Most of the plants are fire-adapted. Many
species can only reproduce via periodic fires
This biome has high biodiversity, with a
great deal of endemism. Endemism is when
species are found in one place only
This biome is rather uncommon, being
confined to relatively few locations with a
Mediterranean climate, California, Costal
South America, South Africa, the
Mediterranean, and Western Australia
Grasslands




Grasses and forbs dominate. Fire and
grazing prevent the establishment of shrubs
and trees
Moderate to low rainfall and a wide range of
temperatures permit grasslands
Seasonal drought, occasional fires, and
grazing by herbivores prevent the
establishment of trees as the dominant
vegetation
Grasslands are a widespread biome;
examples include the Prairies of North
America, the Steppes of Asia, the Pampas
of Argentina, the Veldts of South Africa, and
the Puszta of Hungary.
Savannah
Savannah is grassland mixed with scattered trees
(sometimes it is considered its own biome.).
Temperate Deciduous Forests





Moderate rainfall and mild to warm
summers with cool to cold winters.
Occur at mid-latitudes, where moisture is
sufficient to support the growth of large
trees
Winters are cold enough to prohibit
photosynthesis, and most organisms go
dormant or hibernate over the winter
Dense stands of deciduous trees
predominate
Trees tend to have distinct vertical layers;
including one or two strata of trees and an
understory of shrubs
Tropical Rain Forests






The most productive biome on the planet,
also harbors the most biodiversity.
Most are located near the equator, where
temperatures are warm and relatively
constant year round
Plants are broad-leafed evergreen trees,
shrubs, woody vines, and epiphytes.
epiphytes-plants that live on other plants,
usually trees. Examples include orchids
and mistletoe
High rainfall-usually with a pronounced rainy
season and dry season.
Competition for light is intense. Pronounced
stratification with several layers of trees.
Tropical Dry Forests
tend to occur in lowland areas, where
the distinction between the wet season
and the dry season can be very
pronounced
 deciduous trees, thorny shrubs, and
succulents are very common

Though they are useful as a first
sketch of what is in an area, biomes
are a rough sketch. A grassland in
South Dakota is very different from a
grassland in South Africa.
 Ecoregions are more specific,
accounting for soil, climate, climate,
vegetation, and history. It is a
heirachial scheme.
 Domain is the broadest

– within domains are Divisions
– within divisions are Provinces
Aquatic communities are
determined by the availability of
sunlight and nutrients
 The term “biome” is not generally
applied to aquatic environments, though
the oceans have been broken into
oceanic regions.
 Like terrestrial areas, aquatic
environments include huge volumes of
habitat defined by a few basic factors
– The water column itself provides spatial
structure. Within a given oceanic region,
communities are stratified spatially.
Open Ocean





Pelagic Zone: Light penetrates the top few
meters
Except in areas of upwelling, nutrient
concentrations are generally low, because
the remains of dead organisms sink to the
bottom of the ocean.
All organisms are floating or free-swimming
“nekton”. The major producers are
photosynthetic algae.
Abyssal Zone: Nutrients reach this zone
by falling from above.
Light is absent. This zone supports a wide
variety of specially-adapted organisms
Wetlands
Wetlands are areas covered in water that
support aquatic plants
 They range from periodically flooded
regions, to soil that is saturated with water
during the growing season, to permanently
flooded areas
Typical Wetlands
 Estuaries-occur at the mouths of rivers
 Swamps-flooded areas dominated by trees
 Marshes-flooded areas dominated by
sedges and grasses
 Bogs and Fens-have distinctive vegetation
because their soil is either very alkali (fens),
or very acidic (bogs).

For most, but not all groups of
organisms, biodiversity increases
from the poles to the tropics
This is called a latitudinal gradient in
species diversity
 Reason for this pattern is a mystery in
ecology. Four hypotheses-none is
sufficient to explain it alone.
 1) greater productivity in tropics
 2) history
 3) complexity of habitats
 4) less disturbance

History affects what species live in
an area as well.
In the broadest sense, the naturalist
Alfred Russel Wallace broke the world
into several “biogeographic realms”.
 Which species occur in each region
are determined by historical and
evolutionary factors.
