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Chapter
18 – Ecology of Organisms and Populations ________________________________________________________________________________________________ I. Overview of Ecology A.
Ecology – study of interactions between organisms and their
environments
1. Abiotic – nonliving-
chem and phys factors eg. Temp, light, water etc
2. biotic – all other
living components B.
Science of ecology
1. observation
2. experimental C.
Hierarchy of interactions
1. organismal
ecology- adaptations that enable organism to be successful
2. population
eco– factors that affect pop density and distribution
3. community eco –
interactions of living organisms – predation, competition, mutualism
4. ecosystem eco. - energy
flow and chem cycling
6. biosphere- global
ecosytems D.
ecology vs. environmentalism -
2. environmentalism vs.
science E.
abiotic factors of biosphere
1. patchiness at several
layers
a. regional differences in
climate
b. landforms and topography
c. habitats
d. microhabitats
2. sunlight – distribution
of plants- then animals
3. water – terrestrial and
aquatic animals have to solve different problems
a. drying out vs. lysis of
cells
4. temperature 32- 122 F for
most, some have adaptations (fig. 18.9)
5. wind –
a. some orgs need
nutrients blown to them by wind – proks on mountains; or blow pollen or
seeds around
b. wind chill, convection
heating
6. rocks and soil- physical
structure and chem composition determines plant life, and in stream areas,
water chemistry
7. periodic disturbance-
fire, flood, hurricanes etc. frequent
in some ecosystems II. Evolutionary Adaptations of Organisms A.
Physiological responses
1., more red blood cells, eg.
2. acclimation – several
weeks or months B.
anatomical responses
1. goose bumps, increase in
fur
, eg C.
behavioral responses
1. move to new location- eg.
migration
III.
Population structure and dynamics: A.
Density and dispersion patterns are important population variables
1. Density - number of
individs of a particular species per unit area or volume - eg.
a. number of oak trees per
km2, or
b. number of earthworms/m3
in soil.
2. Usually, you can’t
count every individual so sampling allows estimates;
a. f or example, instead of counting all the individuals of alligators in
the Everglades, plots.
b. the more plots you have, the more closely you approximate true
numbers.
c. sometimes you don’t
count actual individuals, but indirect methods-
d. scat or tracks, or bird songs, for example.
e. nests, or burrows.
3. mark and recapture - N =marked
# in first catch x total catch 2nd time
recaptured marked individuals
a. you might use this method
for voles in a meadow
b. catch particular number
in first attempt, then wait 2 weeks and try again
c. eg 50 voles caught and
marked in 1st attempt, 100 second time, 5 recaptured
1. 50x100 = 5000;
5000/5 = 1000 voles estimated to be in meadow
d. this method assumes marked individuals have the same chance of being
caught as
unmarked.
e. Problems with this
assumption? animal may be more
interested in food or wary of trap
5. Dispersion pattern -
spacing of individuals in an area.
a. uniform - even pattern of
dispersion - nesting birds
b. random - spaced in patternless, unpredictable way - clams in a mudflat
when resources are
plentiful, or when
conflicting needs for diff’t resources creates chaotic pattern
c. clumped - individuals
aggregated in patches - most common dispersal pattern,
often results from uneven distribution of resources B.
Growth Models help us understand population growth
1. idealized models help us
understand population growth
a. Exponential growth -
unrestricted growth
1) G = rN
a) G = growth rate
b) N = size of population
c) r = intrinsic rate of
increase; organisms inherent capacity to reproduce
(roughly birth - deaths for the period being discussed
d) J curve
b. Logistic model - limits
on growth
1) G = rN(K - N) K
a) K
is Carrying Capacity
b) overshooting carrying
capacity may cause population crash, drop in K
c) K
doesn't influence the equation very much until N starts getting large
relative to K. d)
when K is reached, (K-N)/K =
0 and growth rate is zero
e) growth rate is small when
population is very small and very large;
f) growth rate is largest when N is intermediate level of K C.
Multiple factors may limit population growth
1. logistic model - as pop
density increases, population growth slows
a. decrease in birth rate
b. increase in death rate
c. both of the above
2. Density Dependent factors
- decrease growth rate or increase death rate
a. food - - song sparrows
clutch size decrease as pop increases
b. shelter/space - thin seedlings to achieve best productivity of plants
c. build up of toxins
d. disease -
1. high pops of mice,
woodchucks other rodents decrease growth rate even when
more food, shelter supplied -
a) stress hormones increase
b) shrinks repro
organs,
c) delays sexual maturation,
d) depresses immune system
e. predator interest in
large pops
3. Density independent
factors
a. climate
b. weather
- some pops, especially insects, boom until change in conditions, then
bust dramatically, with no leveling off.
c. natural catastrophes
4. Most pops have regular
fluctuation in numbers -
a. song sparrow pops respond to many interactions of density dependent and
independent
factors D.
Some pops have boom bust cycles -
1. predator prey
relationships - Canadian lynx and snowshoe hare every 10 yrs.
2. food supply of prey
affects predator pops, but why does hare pop boom and bust?
3. food supply of prey, over
exploitation by predators, both predation and food supply
4. hormones and stress also
may affect prey pops, coincidentally keeping predator pops from
getting too large
5. time lag in response to
prey increase by predator populations - reproduce more slowly
IV. Life Histories and their Evolution A.
Life tables- track mortality and survivorship in populations.
1. Life tables allow us to
track mortality over time, insurance companies produce these and set
premium rates using these numbers. Info
used to make survivorship curves of difft species
2. survivorship curves -
a. type I - whales,
elephants and humans - have a few young, care for them, increase survival
to maturity
b. type II - some rodents
and hydras - constant death rate-
c. type III - oysters, lots
of marine animals - high death rates for the very young, then low
death rates for those few individuals that survive to adulthood B.
Evolution shapes life history-
1. Life history includes
events from birth thru reproduction to death in a species
2. include age at first
reproduction
a. frequency of reproduction
b. number of offspring
c. amount of parental care
given
d. energy cost of
reproduction
3. Natural selection will
favor combination of life history traits that maximizes and individuals output
of
viable offspring, just as it shapes physical features
a. opportunistic life
history - small animals, reproduce when young, many offspring
b. equilibrial life history
- larger animals, reproduce later, few offspring
4. cichlids (eat larger guppies) vs.
killifish (eat smaller guppies) as guppie predators
a. guppies in cichlid pools
tend to be smaller, mature earlier, have more offspring
b. guppies from both pools
raised in lab w/ no predators kept their differences - heritable
5. r - selection - life
history traits that maximize success in uncrowded, unpredictable surroundings
a. mature early
b. large numbers of
offspring
c. weeds, insects, many
invertebrates
6. K - selection - organisms
w/ pops close to K of environment
a. maturity and reproduction
at later age
b. few, large, well cared
for offspring
c. polar bears, giraffes,
humans V. Human Population A.
continuous growth for over 1000 yrs.
1. at ~ 8000 bc - hunter gatherer to ag
2. plague
3. industrialization at 1700
4. falling death rates
largely causing pop growth
5. technological vs.
biological changes
6. fluctuations around
carrying capacity - exceed by a lot?
a. human population no
longer fits comfortably on earth
b. in order for us to
accommodate all the people expected on earth by 2025 and improve diet,
we have to double food production
c. all arable land is
currently being farmed
d. oceans currently being
overfished
e. 2/3 of all the available
water on earth will have to be in use
7. ecological footprints -
amt of land in ha (hectare - 2.47 ac) per person, current demand on resources
a. US uses 8.4 ha/person;
Bangladesh, India - .8 & .5
b. black means you are using
more land than your country has,
blue means you are within
your country’s limits
c. Earth isn’t big enough
to support whole human pop at US standards B.
Age structure and birth and death rates affect how a pop will grow in the
future
1. Some developed countries
have stable population rates; eg.
Sweden
2. most undeveloped
countries high pop growth rates - 80% of world pop is in LDC, most of current
population growth is occurring in these nations
3. in 48 of LDC, pop growth
is expected to triple by 2050; current
models suggest that US pop will
hit 390 from 270 currently by 2050
4. China’s pop growth rate
- in 1970, 5.9 kids/family; 1999
1.85; still, it will take 30 yrs
for pop growth
to show effects - why?
5. US, Japan, Canada,
Europe, pop growth nearing equilibrium - birth rates at or below replacement
level, though pops are still increasing in some countries, (including
US).
6. about a 30 yr. time lag
from when birth rates drop to population growth stops
7. Demographic transition -
death rate drops before birth rate falls - occurs w/ increase in living
standards, education, social security, especially education of women
8. Age structure of a
population is proportion of individuals in different age groups (Fig. 35.9B)
a. high pop of children
indicates probable explosive growth -
1. at least 60 countries are
in the midst of demographic transition -
2. 40% of population is <
15 yr old, death rate is slowing especially for children.
3. better for demographic
transition, or enforced birth/population control?
b. in developed countries, a
high G results from birth rates and immigration > death rates
c. In US, immigration (legal
and illegal) represents 40% of our current growth, birth rate >
death rate
d. US pop projected to
increase from 270 million today to 390 million in 2050.
e. In stable countries such
as Denmark and Austria, birth rate = death rate, stable structure
f. Different social problems
1. Developing - working age
people unemployed, infant care and schools
2. developed- health care
for the older pop, social security?
1. delaying reproduction
2. decreasing pop thru
decrease in birth rate, not increase in death rate C.
Principles of Population ecology have practical applications
1. management of natural
resources can mitigate human effects on natural systems
2. Principles of population
ecology can be used in this management
3. Wildlife and fisheries
managers as well as foresters try to practice renewable resource management
- harvesting crops w/out damaging resource
4. maximum sustained yield -
consistent yield that can be obtained continuously, w/out harming the
original population
a. intermediate growth rates
the highest - so harvest pops that are far below K, but not too far
b. frequently we don’t
have all the info we need (Fig. 35.10A)
1. estimates were too high
2. discarding smaller cod
caused higher than predicted mortality rate
5. spp in decline or facing
extinction, we try to increase populations - Endangered spp program
a. red cockaded woodpecker -
success story - brought back from near extinction by producing
and preserving pockets of older pines and decreasing understory w/ fire
mgt. - habitat
requirements of that species
6. Integrated Pest
Management (IPM) used to decrease pesticides and control pests - control a.
excessive populations Homework Q’s/Lesson
Objectives 1.
Describe the science of ecology, and list some examples of each
component. 2.
List and briefly describe 2 ways that scientists study ecology . 3.
List and briefly describe the hierarchy of interactions
in ecology and some examples of each. 4.
Contrast ecology with environmentalism.
Who was Rachel Carson? 5.
Describe several abiotic factors and examples of their effects on
organisms. 6.
Describe some evolutionary adaptations of organisms to their
environments. 7.
Describe examples of acclimation. 8.
Provide examples of physiological, anatomical and behavioral responses to
abiotic factors. 9.
Explain how density and dispersion describe populations and how each of
these variables is measured, both directly and indirectly. 10.
Explain the mark and recapture sampling method. 11.
Distinguish between exponential and logistic models of population growth,
explaining the effects of existing population size and carrying capacity on
growth rate. 12.
Be able to draw and explain J and S curves and their axes, and relevant
important points about each. 13.
Differentiate between density dependent and density independent factors
that limit population growth. 14.
Describe the interrelationships among predator, prey and prey food that
cause boom-bust cycles. 15.
Name the attributes of life histories.
Describe how natural selection affects life histories. 16.
Draw survivorship curves I, II, and III;
describe life history characteristics of each and give examples of
organisms. 17.
Distinguish between r and K selected species. 18.
Discuss life tables and age structure diagrams, and examine them for
human populations. Compare an age
structure diagram of a stable population with an explosively growing population
and a declining population. 19.
What issues face a growing population?
A declining population? 20.
Outline the history of human growth of the population, including factors
that affect growth. 21.
Describe demographic transition. Do
you think government regulation of population is ethical?
Support your answer in 2 or 3 sentences. 22.
How has the field of population ecology been used to manage populations
we are trying to regulate? |
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For questions or comments, please contact Sue Kloss - kloss@ltcc.edu |