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BILD midterm curve (8 AM lecture) A - 128 150 (> 20% of scores) B - 112 127 (> next 30%) C - 82 111 (> next 40%) Median 111 (C+) (74% of the points) Mean 109 (73% of the points) Your final letter grade will be based on your TOTAL number of points. The curve will change between now and the end of quarter, as quizzes, activities, clickers points and the final are included.
BILD 3 midterm curve (5 PM lecture) A - 118 150 (> 20% of scores) B - 104 117 (> next 30%) C - 78 103 (> next 40%) Median 103 (C+) (69% of the points) Mean 101 (67% of the points) Your final letter grade will be based on your TOTAL number of points. The curve will change between now and the end of quarter, as quizzes, activities, clickers points and the final are included.
Overview - Population Ecology I. Population density II. Population dispersion III. Demography - Life tables IV. Life Histories V. Population growth Exponential Logistic VI. Population regulation VII. Human population growth
N (K N) = rmax N t K
According to the logistic growth equation, a. The number of individuals added per unit time is greatest when N is close to zero b. The growth rate (rmax) increases as N approaches K c. Population growth (
N ) is zero when N = K t
d. The population grows exponentially when K is small
e. The birth rate (b) approaches zero as N approaches K
VI. Population regulation
What environmental factors stop a population from growing? Why do some populations show radical fluctuations in size over time, while others remain stable?
VI. Population regulation
A. Density dependence/independence B. Metapopulations
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Population Regulation
Density-independent factors
Affect a species independent of its density
Disturbance (landslide, fire, weather)
Types of density-dependent population regulation 1. Intraspecific competition for resources 2. Density-dependent predation 3. Territoriality 4. Density-dependent disease spread 5. Wastes 6. Intrinsic factors
Density-dependent factors
Birth and/or death rates change with density
1. Competition for Resources As density increases, individual reproduction decreases
2. Density dependent predation
10,000
4.0 3.8
Average number of seeds per reproducing individual (log scale)
1,000
Average clutch size
3.6 3.4 3.2 3.0 2.8 0 10 20 30 40 50 60 70 80
100 0 0 10 100 Seeds planted per m2
Density of females (b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply.
(a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases.
Trout preferentially prey on the most abundant insect species in a stream
3. Territoriality
Figure 52.16
Fly fisherman - good entomologists Need to know what insects most abundant Trout preferences density-dependent
Cheetahs are highly territorial; use chemical communication warn to other cheetahs of their boundaries
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3. Territoriality
4. Density dependent disease spread
TB spread by bacteria in droplets, sneeze, cough, spit, etc
Figure 52.17
TB - better transmission in densely populated urban areas than rural areas
Gannets defend nesting sites
5. Wastes
6. Intrinsic factors (physiological)
Wine - alcohol by-product of yeast fermentation Wine - producing yeast can not tolerate high concentration Wine - alcohol content 14% or lower
White -footed mice lower reproductive rates in crowded conditions Why? More aggressive interactions Maybe interactions trigger stress hormones that delay sexual maturity, depress immune system, etc?
B. Metapopulations and Immigration
Metapopulations - are groups of populations linked by immigration and emigration Metapopulation structure can be a buffer against extinction
Glanville fritillary Extinct over much of range land Islands, Finland Why?
A particular population may go extinct from time to time but then be re-colonized by immigrants from other populations This protects the entire system from extinction
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Larvae feed on only 2 species of host plant Plants - open meadows Habitats easy to identify
land Islands - habitat patches (green) Fritillary population metapopulations (yellow) Some patches are occupied, others arent Over time, some populations go extinct Eventually
Has the metapopulation structure of fritillaries helped to prevent their extinction?
Metapopulations of fritillaries Some populations go extinct Mark recapture study migration from occupied to unoccupied patches If habitats close/ connected, extinction balanced by recolonization
mark-recapture study
Metapopulation dynamics can stabilize population at large scale
VII. The Global Human Population The US Census Bureau World Population Clock:
http://www.census.gov/main/www/popclock.html
The Global Human Population The human population increased relatively slowly until about 1650, then grew exponentially
Figure 53.22
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Though the global population is still growing, the rate of growth began to slow approximately 40 years ago
Age Structure age structure - the relative number of individuals at each age affects a countrys future growth
Text fig. 53.23
Age structure is commonly represented as a
Estimates of Carrying Capacity The carrying capacity of Earth for humans is uncertain Increases in food production can increase the carrying capacity, but only within limits How many people the earth can support depends on lifestyle resource use (more on this in ecosystems)
pyramids
Fig. 53.25
Population Ecology Summary I. Population density II. Population dispersion III. Demography - Life tables IV. Life Histories V. Population growth A. exponential B. logistic VI. Population regulation A. Density dependence/independence B. Metapopulations VII. Human population growth size, age structure, carrying capacity
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