Download Lecture_18.1,18.2_Ecology_and_lecture_19_Populations

Lecture 18 Ecology
•
Ecology: the study of relationships and interactions among organisms and their
environment
What’s involved?
Predator-prey relationships
Feeding relationships
Habitats and niches
Availability of nutrients
Pollution and habitat degradation
•
•
•
•
•
•
Ecosystem: a community and its abiotic (non-living) environment
Population: a group of organisms of the same species (capable of interbreeding)
that live in the same area at the same time
Community: a group of populations living and interacting with each other
Species: a group of organisms of similar appearance and which can interbreed to
produce viable offspring (offspring can live to maturity and produce their own
offspring)
Habitat: the physical area in which individuals of a certain species exist
Biosphere: the portion of the Earth and its atmosphere that can support life; the total
of all areas where living things are found, including the deep ocean and lower
atmosphere
Organism
Many organisms make up a population
Population
Many populations make up a community
Community
Many communities make up an ecosystem
Ecosystem
Many ecosystems make
up a biosphere
This is where
abiotic factors
come into play!!!
Biosphere
• Autotroph/producer: an organism that makes organic molecules from
inorganic molecules using light or chemical energy
– “self-feeder”
– Photoautotrophs: undergo photosynthesis; use light energy to convert inorganic
carbon (CO2) into organic compounds
– Chemoautotrophs: break down inorganic chemicals by chemosynthesis to form
organic compounds
– Examples: algae, some bacteria, plants
• Heterotroph/consumer: an organism which eats other organisms to obtain
energy and organic molecules
Example - us
• Detritivore: an organism which ingests dead organic material
– Examples: scavengers, earthworms
• Saprotroph/decomposer: an organism that feeds on dead organic matter
using extracellular digestion
– Specialized detritivores!
– Consume cellulose (plant matter) and nitrogenous wastes (i.e. poop)
– Examples: fungi and bacteria
Communities
and
Ecosystems
• Food chain: a sequence
of trophic relationships in
which one population
feeds on another .
• Trophic level: a step on
a food chain or food web
4.1
Communities
and
Ecosystems
• Food web: a
diagram that
shows all of the
feeding
relationships in
a community
Energy pyramid
Fourth trophic level
Third trophic level
Second trophic
level
First trophic
level
Tertiary consumers
Secondary consumers
Primary
consumers
Producers
Communities and Ecosystems
The
Carbon
Cycle
Lecture 19 Populations
• Population size affected by
•
•
•
•
Birth rate
Death rate
Immigration
Emigration
+
+
Immigration
Birth
Population Size
Emigration
Death
Populations
• Sigmoid growth curve involves
– Exponential phase
– Transitional phase
– Plateau phase
Transitional
Exponential
Plateau
Populations
• Exponential growth
– Unlimited
– All organisms can rapidly increase their
population size if there are no factors
controlling their growth
– Birth rate alone controls growth rate
Populations
• Transitional and plateau phases
– The initial rapid increase in population size
slows down (transitional phase) until the rate
of growth is zero (plateau phase)
– When r = 0, the number of individuals in the
population has reached the carrying
capacity—the maximum number of
individuals of a species which can be
sustainably supported by the environment
Populations
• Factors which limit population growth may be
density-dependent or density-independent
– Density-dependent factors
• Affect a larger proportion of the population as the density of
individuals increases
• Examples: mortality due to predation or disease and
intraspecific (within a species) competition
– Density-independent factors
• Affect a proportion of the population regardless of its density
• Example: mortality due to natural disasters (still, if the
population is denser, there will be a greater affect on the
population size even though the proportion affected is
independent of density)
Populations
• Factors which limit population growth may be
extrinsic or intrinsic
– Extrinsic population-limiting mechanisms
• Originate outside of the population and include biotic and
physical factors
• Examples: food supply, predation, disease, weather
– Intrinsic population-limiting mechanisms
• Originate in an organism’s anatomy, physiology, or behavior
• Examples…
– Koalas may reabsorb a developing embryo when conditions
are crowded and resources are limited
– Lemmings migrate in large groups when resources are
depleted
– Competition for resources
Populations
• Ecologists often study a few individuals of a
population in order to draw conclusions about
the entire population
• Random sampling: a method used to ensure
that every individual in a population has an
equal chance of being selected for study
– Quadrat sampling (useful for determining population
size of stationary organisms like plants)
– Mark-Recapture method (useful for determining
population size of organisms that move around)
Populations
1.
2.
3.
4.
5.
6.
7.
Quadrat sampling for estimating population size
(a quadrat is a square area of known size)
A quadrat is placed in the area to be sampled and
grid lines are marked within the transect and
numbered
Two random numbers are selected as coordinates
Individuals within the random square are counted
and the number is recorded
Steps 2 and 3 are repeated as many times as
possible
The total size of the sample area is measured
The mean number of plants per quadrat is calculated
The estimated population size is calculated using the
equation below
Populations
Mark-recapture method for estimating population size
1.
2.
3.
4.
5.
Capture as many individuals as possible in the area to be studied
Mark each captured individual (without making them more
camouflaged or more visible to predators—this would skew
results!)
Release all marked individuals into habitat
Recapture as many individuals as possible and count how many
are marked and how many are unmarked
Calculate the estimated population size using the Lincoln index:
Estimated population size = (n1 * n2) / n3
where n1 = number initially caught and marked
n2 = total number caught on second capture
n3 = number of marked individuals recaptured