BSC 120 Lecture Notes - Lecture 53: Endangered Species Act Of 1973, Snowshoe Hare, Bald Eagle
29 Apr 2018
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Chapters 53, 54, 55, and 56 – Principles of Ecology
I. Principles of Ecology
a. Ecology – the study of interactions between organisms and their environments
b. The environment
i. Two major components:
1. Abiotic component – nonliving chemical and physical factors
2. Biotic component – living factors
c. A hierarchy of interactions
i. Organismal ecology
1. Evolutionary adaptations – enable individual organisms to meet
challenges of abiotic environments
2. Includes physiological ecology
3. Hibernation, adaptations, etc.
4. Camel
a. Hump stores food
b. Slit-like noses so that nostrils can close and not breathe
sand
c. Three eyelids
d. Three layers of eyelashes
e. Hooves allow them to not sink in sand
ii. Population ecology
1. Population – groups of individuals of the same species living
together in a geographically defined area
2. Factors that affect population density and growth
a. Climate
b. Resources
c. Barriers
3. Population Density – number of individuals of a species/unit of
area
a. Estimated by indirect indicators, such as number of bird
nests or rodent burrows
b. Mark-recapture method
i. Animals are trapped, marked, and then recaptured
after a period of time
ii. How many were there vs how many are there now
iii. Allows us to predict where an endangered species
may collapse
1. Ex: bald eagle
2. 20% of all birds are threatened or
endangered
a. Ex: passenger pigeon (used in
WWII) now extinct
4. Population Age Structure
a. Proportion of individuals in different age groups
b. Can help us understand the history of a population’s
survival or reproductive success and how it relates to
environmental factors
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Chapters 53, 54, 55, and 56 – Principles of Ecology
c. Useful tool for predicting future changes in a population
d. Two major factors that influence population growth rate
i. Birth rate
ii. Death rate
e. Two models
i. Exponential growth model
1. Describes the rate of expansion of a
population under ideal, unregulated
conditions
2. 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
ii. Logistic growth model
1. In nature, a population may grow
exponentially for a while, but eventually one
or more environmental factors will limit its
growth
a. Food supplies
b. Living space
c. Interactions with other organisms
2. Population-limiting factors restrict
population growth
3. Logistic Growth Model describes growth of
an idealized population that is slowed by
limiting factors
a. Intraspecies competition (within)
b. Carrying capacity – the number of
individuals in a population that the
environment can just maintain with
no net increase or decrease
5. Population Cycles
a. Boom-and-bust cycles of the snowshoe hare and one of its
predators, the lynx
b. Bust cycles of rabbits in Australia
6. Applications of Population Ecology
a. Challenge for conservation biology is to determine why a
population is in decline and try to remedy the situation
b. US Endangered Species Act of 1973
i. Defines an endangered species as one that is in
danger of extinction throughout all of a significant
portion of its range
ii. Defines a threatened species as one likely to
become endangered in the foreseeable future
7. Human Population Growth
a. Has been growing exponentially for centuries
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Chapters 53, 54, 55, and 56 – Principles of Ecology
b. Based on the same parameters that affect other populations:
birth rates and death rates
c. Unique – we can control is with voluntary contraception
and government-sponsored family planning
d. Technology has increased Earth’s carrying capacity, but no
population can grow indefinitely
e. Increases in the human population result in more people
consuming resources and dumping pollutants into the
biosphere
iii. Community ecology
1. Is concerned with communities (assemblages of populations of
different species living close enough for potential interactions)
2. Focuses no how interactions between species affect community
structure and organization
3. Ask questions about interspecific interactions (between different
species)
a. When two or more species in a community rely on similar
limiting resources
b. May limit population growth of the competing species
c. How do species interact?
i. Classified as whether they are
1. Beneficial to one or both species involved
a. Mutualism (+/+)
i. Both benefit
ii. Yucca moth pollinates and
feeds on the Yucca plant
iii. Acacia ants defend acacia
trees and are fed by the tree
in which they life
iv. Lichens and mycorrhizae
b. Commensalism (+/0)
i. Beneficial to one but of
neutral benefit to the other
ii. Cattle egrets follow cattle to
feed on insects stirred up by
the grazing cattle
2. Detrimental to one of the species involved
a. Parasites (+/-)
i. Smaller organism feeds on a
larger, weakening or killing it
ii. It is usually advantageous to
not kill its host
iii. Ex: tapeworms, roundworms,
mosquitoes, etc.
b. Pathogens (+/-)
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