Transcript Document

Let’s Eat!!
U.S.G.S.
Trophic
levels
What do the First and Second Laws of
Thermodynamics Tell us?
•
•
•
•
First Law: Energy in = Energy Out
Until humans:
Energy =sit by fire, or in the sun
Sun: 30% reflectd, 50% converted to heat,
the rest goes to the water cycle, except
<1% used by plants
• Second Law: No process is 100% efficient
– Energy In = Work + Heat
What is Ecological Efficiency?
• Plants absorb how much sunlight?
– 1-3%
• Herbivores use how much of the plant energy?
– 10%
• Where does the rest go?
– Heat and respiration
• What is the efficiency of a carnivore?
– 10%
• Example: Humans
– 0.02 x 0.1 x0.1 = 0.0002, 2% of the solar energy that
passed through the plant, cow, human
Species interaction tactics
• Unique niches
• Competition--competitive exclusion by
specialization vs. extinction
• Specialization
• Symbiosis--commensalism, mutualism,
parasitism
• Predation
• ==population ecology
Population Ecology
1. Density and
Distribution
2. Growth
a. Exponential
b. Logistic
3. Life Histories
4. Population
Limiting Factors
5. Human
population growth
(Modified from a WWW site that I have lost the reference to!
Examples of applications
•
•
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Invasive species
Endangered species
Pest control (e.g., agriculture)
Human population growth
Population. Individuals of same species occupying same general
area.
Density: the number of organisms in a unit area
Distribution: how the organisms are spaced in the area
Fig. 52.2
Changes in population size
Northern Pintail Duck
Growing
Fig. 52.9
Shrinking
Fig. 52.16
Fluctuating
Fig. 52.19
Questions
• Why do populations change in size?
• What factors determine rates of population
growth or decline?
• How do these differ among species?
2. Population Growth
a. exponential growth
The change in population size (N) in an interval of time is
number of births – number of deaths, or
∆N = B - D
∆t
(ignoring immigration and emigration)
If b (birth rate) is the number of offspring produced
over a period of time by an average individual, and d
(death rate) is the average number of deaths per
individual, then
∆N = bN – dN or
∆N = (b – d)N
∆t
∆t
Population Growth: exponential growth
The difference between the birth rate and the death
rate is the per capita growth rate
r=b-d
The growth equation can be rewritten as
∆N = rN
or
dN = rN
∆t
dt
Exponential growth occurs when resources are
unlimited and the population is small (doesn’t
happen often). The r is maximal (rmax) and it is
called the intrinsic rate of increase.
Population Growth: exponential growth
Note that:
1. r is constant, but N grows
faster as time goes on.
2. What happens with
different r’s in terms of
total numbers and time to
reach those numbers?
Fig. 52.8
r can also be negative (population
decreasing)
if r is zero, the population does not
change in size
thus, the rate of increase (or decrease)
of a population can change over time.
Exponential growth does not happen often:
Fig. 52.9 – Whooping crane
Or indefinitely:
Reindeer on the Pribalof Islands, Bering Sea
reindeer slide
2.b. Logistic growth
Most populations are limited in growth at some carrying
capacity (K) (the maximum population size a habitat can
accommodate)
Fig. 52.11
Logistic Growth Equation: incorporates changes in
growth rate as population size approaches carrying
capacity.
dN = rmaxN (K - N)
dt
K
Fig. 52.10
At what point is the “effective” r the highest?
At what point are the most individuals added to the population?
Are these the same?
Logistic Model
Fig. 52.12
Fits some populations well, but for many there is not stable
carrying capacity and populations fluctuate around some
long-tem average density.
3. Life Histories
• How do we figure out r for different
populations?
• What accounts for different patterns or
rates of population growth among different
species?
– For example, different rmax
How do we figure out r?
a. Life History Tables : follow a cohort from
birth until all are dead.
life history table
Reproduction Tables : follow a cohort from
birth until all are dead.
b. Life history strategies
Life histories are determined by traits that
determine when and how much an
organism reproduces and how well it
survives.
b. Life history strategies
i. reproduction
“big-bang” reproduction
very high reproductive rates
per event
Vs. reproduction for
consecutive years
fewer young produced per
event but often more
parental care
b. Life history strategies
ii. mortality
Survivorship curves
Fig. 52.3
There are often trade-offs between reproduction and survival.
Fig. 52.6 - European kestrel
Reproduction has a cost when energy is limiting.
Fig. 52.5 – Red deer in Scotland
K-selection
3.b. Life history strategies
iii. r- and K-selection
Near carrying capacity natural selection will favor traits that
maximize reproductive success with few resources (high densities).
Density-dependent selection.
r-selection
Below carrying capacity natural selection will favor traits that
maximize reproductive success in uncrowded environments (low
densities).
Density-independent selection.
Density-dependent
Any characteristic that varies according to a
change in population density.
food availability, territories, water, nutrients,
predators/parasites/disease, waste accumulation
Density-independent
Any characteristic that does not vary as
population density changes.
weather events, salinity, temperature
Density dependent: decreased fecundity
Space-limited
Fig. 52.14
Food-limited
Density dependent: decreased survivorship
Fig. 52.15
Density-dependent changes
in birth and death rates slow
population increase.
They represent an example
of negative feedback.
They can stabilize a
population near carrying
capacity.
Fig. 52.13
4. Factors that limit population growth
• Density dependent birth and death rates
(as we just discussed). Many of these
reflect
– competition for resource (food/energy,
nutrients, space/territories).
– predation, parasites, disease
– waste accumulation (e.g., ethanol)
4. Factors that limit population growth
• Density independent survivorship or
mortality
– Extreme weather events
– Fluctuations in wind and water currents
Interactions among population-limiting factors
The dynamics of a population result from the interaction
between biotic and abiotic factors, making natural populations
unstable.
Water temperature,
Competition,
Cannibalism.
Fig. 52.18
Population-Limiting Factors
Some populations have regular boom-and-bust cycles.
Fig. 52.19
Predation
Food shortage in
winter
Prey availability
SUMMARY
Population. Individuals same species occupying same general area.
Have geographic boundaries and population size.
Key characteristics
Density. Individuals per unit of area or volume.
Distribution: uniform, clumped, random.
Demography. Studies changes in population size.
Additions (+) : Births and Immigration.
Subtractions (-) : Deaths and emigration.
Life histories. Affect reproductive output and survival rate and
thus population growth.
Life history strategies are trade-offs between survival and
reproduction.
Population Growth
Exponential. J-shaped. Idealized, occurs in certain conditions.
Logistic. S-shaped. A little more realistic. Carrying capacity.
K-selection. Density-dependent selection.
r-selection. Density independent selection.
Population growth is slowed by changes in birth and death
rates with density.
Interaction of biotic and abiotic factors often results in unstable
population sizes. In some populations they result in regular
cycles.
5. Human population growth
6,417,531,489 people
(as of 9:30, Feb. 8, 2005)
Questions
1. 1. Human growth
For example,
-
What factors are correlated with changes in human
population growth rate?
– How long has Earth’s population been similar to
what it is now?
– Over what time period has the human population
shown the greatest change in numbers?
2. How do the patterns compare with what we
have just studied about natural patterns of
population growth?
3. What new questions does this raise for you?
Human Population= 6,339,110,260 (this morning)
Exponential growth since Industrial Revolution: better nutrition,
medical care and sanitation.
http://www.ibiblio.org/lunarbin/worldpop
Growth rates ( r )
1963: 2.2%(0.022), 1990: 1.6%, 2003: 1.3% (200,234/day), 2015: 1%
Growth will slow
down either due to
decreased births or
increased deaths.
Likely both as
suggested by agestructure pyramids:
relative number of
individuals in each
age-class.
Fig. 52.20
Age-structure pyramids
Fig. 52.22
BELLINGHAM
CensusScope
When and how will human
population growth stop?
• This question is likely to be answered one
way or another in your lifetime.
• What is Earth’s carrying capacity for
human’s?
• Have we already exceeded K?
• What are consequences of human
population growth for other species on this
planet?
Human impact
• Depends on
– Total human population
– Consumption by each individual
– Ecological impact of each unit of consumption
• I = PAT
– P = population
– A = affluence
– T = technology
(Ehrlich and Ehrlich)
Unknown what
the carrying
capacity of Earth
for humans is. A
useful concept is
the ecological
footprint: land
needed to
produce
resources and
absorb wastes
for a given
country.
World Wildlife Fund for Nature
Fig. 52.23 – Ecological footprints for various countries and the world
SUMMARY
Human population has been growing exponentially for a
long time.
A reduction is expected either through lower birth rates or
higher death rates. The age-structure suggest different
scenarios for individual countries.
Humans appear to be above Earth’s carrying capacity.