1. INTRODUCTION TO ECOLOGY
2. ECOLOGICAL EXPERIMENTS
3. ECOLOGICAL GENETICS & ADAPTATION
4. LIMITATIONS TO DISTRIBUTION & ABUNDANCE
5. INTRODUCTION TO POPULATIONS
6. POPULATION GROWTH MODELS
7. DEMOGRAPHY
8. COMPETITION 
9. PREDATION
10. HERBIVORY
11. COMMUNITY PROPERTIES
12. SUCCESSION
13. REGULATION OF SPECIES DIVERSITY WITHIN HABITATS
14. ISLAND BIOGEOGRAPHY
15. COMMUNITY METABOLISM: PRIMARY PRODUCTIVITY & NUTRIENT CYCLING
16. THE CARBON CYCLE & GLOBAL CHANGE
17. CONSERVATION BIOLOGY & The Design of Nature Preserves

1. INTRODUCTION TO ECOLOGY

I. What is ecology?

A. Ecology is the scientific study of the interactions that determine the distribution and abundance of organisms.

1. abiotic factors, e.g. temperature, moisture, light; biotic factors, e.g. predators, disease, competitors

2. Where do organisms live? How many are there? Why?

3. Difficulties: uniqueness and complexity

4. overlaps with physiology, behavior, genetics, evolution and mathematics

B. Goals of ecology

1. description (patterns)

2. functional understanding (processes; proximate explanations)

3. evolutionary understanding (ultimate explanations)

4. document, explain, predict, control

C. Levels of study

1. Organism - individual

2. Population - All the individuals of a species that are found in a given area.

emphasize factors affecting birth and death rates

3. Community - An assemblage of populations of different species found in a given area.
emphasize species interactions.

4. Ecosystem - The biotic community considered together with its physical environment.
emphasize energy flow and nutrient cycling.

5. seek explanations at lower levels, significance for higher levels

D. Approaches to studying ecological questions: role of experiments

1. theoretical

2. laboratory/greenhouse

3. field (i.e., in nature)

II. The scientific method & Hypothesis testing

A. Induction (arguing from specific to general)

1. inductive data: look for patterns, correlations

B. Deduction (proposing an explanatory hypothesis): "If (hypothesis) . . . then (prediction) ..."

1. importance of manipulative experiments

C. Strong inference: mutually exclusive hypotheses, critical tests

REQUIRED READING: Krebs: Preface & Chapter 1

Supplemental Reading: Platt, J.R. 1964. Strong inference. Science 146: 347-353. 

"...in one sense, the distinction between a theoretician, laboratory worker, and field worker is that the theoretician deals with all conceivable worlds while the laboratory worker deals with all possible worlds and the field worker is confined to the real world. The laboratory ecologist must ask the theoretician if the possible world is an interesting one and must ask the field worker if it is at all related to the real one."  Slobodkin....in Ricklefs (1979) p. 25.

"The formulation of a problem is often more essential than its solution." --- A. Einstein

"I cannot give any scientist of any age better advice than this: the intensity of the conviction that a hypothesis is true has no bearing on whether it is true or not." --- P. Medawar. Advice to a Young Scientist.

"Induction is necessary; deduction is powerful." — E. Mayr

2. ECOLOGICAL EXPERIMENTS

I. Manipulative experiments

A. An experimental unit is the smallest division of the experimental material such that any two units may receive different treatments

1. treatment (manipulated) and control units

B. Ways to reduce bias and erroneous interpretations

1. Every treatment must have a control (either no treatment or a sham treatment)

2. The control units must be measured at the same time as the treatment units

3. Replicates are necessary

4. Replicates should be independent; randomized

5. Beware of pseudoreplicates

6. Repetition of experiments

7. Eternal vigilance

II. Types of ecological studies

A. Descriptive

B. Comparative

C. Experimental environments

1. "Natural" (field) vs artificial (lab) environments

REQUIRED READING: class handouts

Supplemental reading:

Hairston, N.G. 1989. Ecological Experiments. Cambridge Univ. Press: NY.

Hurlbert, S.H. 1984. Pseudoreplication and the design of ecological field experiments. Ecology 54: 187-211

Krebs, C.J. 1989. Ecological Methodology. Harper & Row: NY.

Scheiner. S.M. and J. Gurevitch (eds.). 1993. The Design and Analysis of Ecological Experiments. Chapman and Hall: NY.

3. ECOLOGICAL GENETICS & ADAPTATION

I. Natural Selection

A. Darwin's theory of evolution by natural selection (1859)

1. individuals vary

2. variation is heritable

3. variants show differential reproduction

4. variants favored by the environment will increase in populations

5. adaptation

B. Evolution is the cumulative change in the characteristics of organisms over generations.

II. Variation within Species

A. Heritability

1. phenotypes result from the interaction between genotypes and environment

2. are differences among individuals attributable more to genetic differences, or environment?

a. genetic: common gardens, reciprocal transplants, e.g. Achillea millefolium

b. ecotypes, races, local adaptation, (also Anthoxanthum odoratum, later in lecture)

B. Variation and types of selection

1. stabilizing selection: genotypes that generate the mean phenotype are favored

2. directional selection: genotypes that generate one of the extreme phenotypes favored

3. disruptive selection: genotypes that generate the mean phenotype are least fit

III. Adaptation and optimality

A. Adaptation: natural selection favors organisms that are well-matched to their environment

B. Convergence: different lineages evolve similar characteristics in response to similar selective pressures

C. Organisms are typically not optimally-adapted to their environments

1. can only respond to past environments - environments are not stable

2. can only act on available genotypes/phenotypes

D. How can we test whether organisms are optimal? experiments

1. Lack clutch-size model

2. artificially alter clutch size

3. suboptimality a result of tradeoffs

REQUIRED READING:  Krebs: Chapter 2.

Supplemental Reading:
Endler, J.A. 1986. Natural Selection in the Wild. Princeton Univ. Press: Princeton, NJ.

4. LIMITATIONS TO DISTRIBUTION & ABUNDANCE

I. Dispersal: movement of organisms from areas of high density to areas of low density

A. Types of dispersal

1. range expansion vs. movement among already-occupied habitats

2. diffusion vs. jump vs. secular dispersal

B. Examples

1. recolonization of Krakatoa after volcanic eruption

2. recolonization of Mt. St. Helens blast zone

C. Factors that limit (jump) dispersal ability

1. mobility

2. size

3. tradeoffs between mobility and size

4. chance

D. Dispersal limitations on the range of species

1. introduced or invasive species provide evidence of dispersal limitation

2. transplant experiments allow experimental test of dispersal limitation - * but need to prevent accidental introductions

II. Physical factors

A. Conditions (not depleted) vs. resources (depleted)

B. Temperature (and moisture)

1. global patterns are the result of differential heating of equatorial and polar regions

2. global patterns modified by local features

a. continental vs. maritime climates

b. altitude

3. microclimatic modification of local climates

4. direct vs. indirect effects of temperature on distributions

a. direct effects (e.g., Saguaro cactus, North American songbirds)

b. indirect effects (e.g., oxygen concentrations in water)

c. interactions of temperature and moisture

C. Moisture (and temperature)

1. global patterns are the result of differential heating and rising and falling air masses

2. global patterns modified by local features

a. rainshadows (on leeward sides of mountains, mountain ranges)

b. proximity to large bodies of water (e.g., lake-effect snows)

D. Moisture and temperature interact to control distributions

1. plants: experience drought when precipitation > potential evapotranspiration

2. adaptations to deal with drought

a. improve access to water

b. reduce water loss

c. store water

d. avoidance

3. adaptations to deal with high temperatures

a. avoidance in plants and animals

E. Other physical factors

1. Light

a. photoperiod

b. intensity

c. quality

2. Mineral nutrients

a. qualitative (presence/absence of particular minerals/nutrients) vs quantitative differences

b. adaptations: ecotypes, carnivory

3. Space: e.g., territories, open space that can be colonized, etc.

4. pH

a. direct vs. indirect effects

b. can be ameliorated by buffering effect of mineral substrate

5. Fire

F. Fundamental vs. Realized niches

1. fundamental: range of combinations of physical conditions that an individual of a species can tolerate

2. realized: range of conditions under which an organism is actually found

a. is a subset of the fundamental niche

b. is reduced compared to the fundamental niche as the result of interactions with other organisms (interactions with other organisms discussed in Chapter 6)

3. Liebig's law of the minimum & Shelford's law of tolerance

REQUIRED READING:  Krebs Chapters 4, 6, 7; pp. 190-192, 131-135; also the Baja California video

5. INTRODUCTION TO POPULATIONS

I. Populations: a group of individuals of the same species occupying an area at some time

A. Properties of populations

1. geographic range

2. density

3. demographic parameters (rates of birth, death, immigration, emigration)

4. derived characteristics

a. age distribution

b. genetic composition

c. dispersion (distribution of individuals in space)

B. Dispersion: clumped vs. uniform vs. random

1. pattern may suggest process

2. pattern is sensitive to scale

C. Density: number of individuals/unit area or volume or biomass/unit area or volume

1. estimating absolute density

a. sessile organisms: quadrat sampling, line transects

b. mobile organisms: capture-recapture, depletion sampling

2. estimating relative density:  trapping, fecal pellets, pelt records, roadside counts

REQUIRED READING: Krebs Chapter 9

6. POPULATION GROWTH MODELS

I. Growth in an unlimited environment

A. Geometric growth model: discrete reproduction, non-overlapping generations

N_t+1 = N_t R   --OR--   Nt = N_o R^t

where:
N_o = initial population size
N_t = population size at time t (note: t = number of generations)
N_t+1 = population size at time t+1
R = net reproductive rate

II. Density-dependent growth in a limited environment: Logistic growth model

dN/dt = rN [(K - N) / K]

where  K = the carrying capacity = the maximum number of individuals the environment can support indefinitely; stable equilibrium.

--> when N is near zero:    dN/dt = rN    (approximately exponential growth)

--> when N is near K:    dN/dt = 0    (approximately no growth)

Assumptions of the logistic model

1. no immigration or emigration

2. the population has overlapping generations and continuous breeding season.

3. r and K are constants, r is small

4. all individuals are equivalently affected by crowding

5. effects of density are instantaneous: no time lags

6. linear density effects on per capita growth rate

REQUIRED READINGS: Krebs Chapter 11

7. DEMOGRAPHY: The empirical study of population growth and age-specific survivorship and fecundity.

I. Cohort life tables: (cohort = group of individuals born in the same time interval)

A. Survivorship

x = age interval (from x to x+1)

n_x = no. of survivors at start of interval x

l_x = survivorship = n_x / n_o = proportion of original cohort that are alive at start of interval x

B. Survivorship curves: three main types--I, II, III. (plot log₁₀ n_x against x)

C. Fecundity:  b_x = fecundity = mean no. of females born per female at age x

D. Mortality

d_x = number dying during the interval x to x+1; d_x = n_x - n_x+1

q_x = age-specific rate of mortality during interval x; 
q_x = d_x / n_x

II. Estimating population growth rate from life tables (often count only females in life tables: why?)

Formula: r = ln R_o / G

Estimating components of formula

R_o = net reproductive rate
    = (daughters born in generation t+1) / (daughters born in generation t)

ESTIMATED BY: R_o = S 1_xb_x (i.e., multiplication rate per generation)

G = generation time = average interval between birth of parents and birth of offspring

G = S x1_xb_x / S 1_xb_x

III. Reproductive value: expectation of current and future (residual) fecundity

A. Reproductive value = V_x = b_x + S l_xb_x (across age intervals > x)

B. Residual reproductive value important in understanding evolution of life-history traits

REQUIRED READING: Krebs Chapter 10

8. COMPETITION 

I. Types of competition

A. Resource (exploitative, scramble)

B. Interference (contest)

II. Analytical model of competition

III. Competitive exclusion principle

A. Gause: "complete competitors cannot coexist"

B. Reasons for exceptions

1. non-equilibrium coexistence

a. fluctuating environments

b. disturbance/predators

c. regional coexistence

2. populations not resource-limited

3. constant immigration

4. niche differentiation

a. resource partitioning

b. spatial and temporal separation in resource use - e.g., warblers

c. character displacement - e.g., Darwin's finches:  comparison of areas of sympatry and allopatry

IV. How to demonstrate competition? (vs. invoking the "ghost of competition past")

A. What needs to be documented?

1. niche overlap

2. reduction in population density (survivorship and/or fecundity)

B. How?

1. enclosure experiments

2. removal experiments

D. Evidence for competition

1. Schoener (1983)

2. Connell (1983)

(3. also see Strong, Lawton, and Southwood (1984))

REQUIRED READING: Krebs Chapter 12, relevant sections in Chapter 6

Literature:

Brown, J. and D. Davidson. 1977. Competition between seed-eating rodents and ants in desert ecosystems. Science 196:880-882.

Connell, J. H. 1983. On the prevalence and relative importance of interspecific competition: evidence from field experiments. American Naturalist 122:661-696.

Lack, D. 1971. Ecological Isolation in Birds. Blackwell Scientific Publications, Oxford.

Schoener, T. W. 1983. Field experiments on interspecific competition. American Naturalist 122:240-285.

Strong, D. R. Jr., J. H. Lawton, and T. R. E. Southwood. 1984. Insects on Plants: Community Patterns and Mechanisms. Blackwell Scientific Publications, Oxford.

Werner, E. E. and D. J. Hall. 1976. Niche shifts in sunfishes: experimental evidence and significance. Science 191:404-406.

9. PREDATION

I. Predation: one organism eats all or part of another

A. "true" or typical predation: consumed individual is killed in the process

B. grazing: part of an organism is eaten, not killed in the process

II. Lab experiments involving predation

A. Gause (1934): Paramecium (prey) and Didinium (predator)

1. coexistence only occurred if included "immigration" of prey species

2. conclusion: predator-prey systems inherently unstable

3. possible outcomes of competition

B. Huffaker (1958): herbivorous mite (prey) and predatory mite on oranges -- coexistence only occurred if added substantial environmental heterogeneity

III. Examples of stable coexistence of predators and prey in field (from biological control literature)

A. Cottony-cushion scale in California (introduced insect pest on citrus)

1. controlled by introduction of vedalia beetles (natural predator in native habitat)

2. stable coexistence (at low population levels) until began spraying DDT (killed predators)

B. Opuntia stricta (prickly pear cactus) in Australia

1. controlled by introduction of Cactoblastis cactorum (moth)

2. larvae of moth feed on pads of cactus

a. direct effects (feeding damage)

b. indirect effects (pathgogens enter via feeding wounds)

3. stable coexistence because females lay eggs in clumps - not all cacti are killed

a. not all cacti are infested by moth larvae

b. larvae don't migrate from one host to another

IV. Models of predator-prey population dynamics

A. Lotka-Volterra models - considered unrealistic (!)

B. Rosenzweig & MacArthur's (1963) graphical model

1. construct zero net growth isoclines (ZNGIs) for prey and predator

2. prey isocline

a. often expected to be hump-shaped

i. "Allee effect" - initial positive effect of increasing density

ii. negative density-dependent effects at high density (approaches K)

b. prey population increases from points under the curve, decreases above

3. predator isocline

a. shifted to the right of the origin (minimum number of prey for them to survive)

b. flattens out (things other than prey limit population)

c. predator population increases from points under the curve, decreases from points above the curve (too few prey, so starve, or not enough territories, so don't reproduce)

4. possible outcomes of predation: overlap ZNGIs, draw vectors

a. stable coexistence: convergent (damped) oscillations of both predator and prey

b. ~stable coexistence: coupled oscillations of predator and prey populations

c. other possibilities include extinction and multiple stable equilibria, depending on the particular shapes and combinations of the ZNGIs

V. Ways in which predators can respond to prey populations

A. Numerical response: increased reproduction due to increased food availability

B. Functional response: as prey population increases, each predator eats more individuals of prey per unit time

1. typically rises and then flattens out, though the shape of the curve may be different for different systems (type 1,2,3 functional response curves)

C. Aggregative response: predators aggregate where prey is most abundant, or spend more time foraging in areas where prey is more abundant

D. Developmental response: growth rates of (individual) predators increase with increasing food availability

E. Total response

1. is the result of combinations of different individual types of response

2. often, predator has strongest effect on prey density when the prey population is relatively small

VI. Field experiments: results and difficulties

A. Ruffed grouse in NY

1. removed predators from one area, left another as control

2. decreased nest losses, but no change in chick mortality, adult loss, overall population size

3. difficulties: migration, recolonization of both predator and prey not controlled for

B. Dingoes in Australia

1. dingo fence and extermination excluded dingoes from a large area of eastern Australia

2. prey species (red kangaroos, emus) abundant where dingoes excluded

C. Prey-switching

1. as prey density decreases, search time for predator increases

2. when returns per unit effort (energy/time) decrease sufficiently, switch to other prey

3. may help stabilize both predator and prey populations

a. more stable food supply for predator

b. (temporarily) reduced predation pressure on prey populations

D. Other interactions are occurring simulataneously

1. explicit consideration in determining the shape of ZNGIs

2. example: lynx/snowshoe hare populations show coupled oscillations

a. intrinsic cycling of predator and prey populations?

b. intrinsic cycling in hares that in turn affects lynx population?

i. intrinsic cycling of hares
(high r?, time lag? food-limited or predation-limited?

ii. hares decline during winter food shortages

iii. lynx decline in response to fewer prey (not as a result of predation)

VII. Defenses, counter-offenses, and counter-defenses

A. Avoiding being eaten

1. advertise distastefulness

2. false advertisement

3. camouflage

B. Coevolutionary arms race? not entirely

1. the "life-dinner" principle

2. a single species of predator can't evolve to catch all prey; likewise, a single species of prey can't evolve to elude all predators

3. if older/weaker prey are eaten, natural selection to avoid becoming prey might be weak

REQUIRED READING: Krebs Chapter 13, pp. 333-337, relevant sections in Chapter 6

10. HERBIVORY: animals eating plants

I. The world is green: implications?

A. Not many herbivores? (no, there are many herbivores)

B. Herbivory is inconsequential to plants? (no, herbivory affects growth, survival, fecundity)

C. Not all plant tissue is food? (yes)

D. Herbivore populations limited by things other than food? (yes)

II. Plant defenses against herbivory

A. Structural defenses

1. examples: thorns, hairs, egg mimicry

2. can be induced by grazing: e.g., Opuntia (also occurs in grazed animals)

B. Animal defenses: ant-plant mutualisms

1. e.g., swollen-thorn acacia and Psuedomyrmex ants

2. role of extra-floral nectaries in attracting ants

C. Chemical defenses: secondary chemicals ( = allelochemicals

1. e.g., oxalic acid, cyanide, glycosides, alkaloids, terpenoids, saponins, flavenoids, tannins

2. functions of secondary plant compounds?

a. by-product of normal metabolism? (Muller 1970) probably not

b. to deter herbivores (Ehrlich & Raven 1964)

3. patterns that suggest secondary compounds are defensive

a. production induced by herbivory

b. concentration of compounds in valuable tissues

c. energetic cost of producing them, maintaining them

d. change in production in response to environmental stress

4. do secondary compounds affect herbivores?

a. e.g., winter moth on oak leaves

i. natural pattern, experimental tests of hypotheses

b. e.g., Monarch butterfly larvae and milkweed cardiac glycosides

III. General theories of plant defense strategies

A. Apparency theory (Feeny 1976, Rhoades & Cates 1976)

1. "apparent" plants are bound to be found, should have defense against generalized herbivores

a. quantitative defenses favored

b. difficult for herbivores to circumvent defense

2. "unapparent" plants are unlikely to be found

a. defense by escape in time or space

b. qualitative defenses favored

c. possible for some specialist herbivores to circumvent defense

3. problems with the theory:  how to define "apparency" objectively

B. Resource-availability theory (Coley et al. 1985)

1. resource availability affects ability to produce defenses, and ability to replace lost tissue

2. when resources are abundant:

a. low investment in defense (tissues easy to replace)

b. use qualitative defenses (because can afford the high cost of production and maintenance)

3. when resources are scarce:

a. high investment in defense (tissues are costly to replace)

b. use quantitative defenses (because cheaper and last longer)

IV. Interactions between plant and herbivore populations

A. Interactive grazing

1. abundance of vegetation affected by abundance of herbivore:  demonstrated experimentally by use of exclosures

2. often see irruptions (rapid increase and collapse of populations)

a. common in introduced as well as natural populations

i. reindeer on islands

ii. lemmings

iii. insect herbivores (e.g. spruce budworm)

b. plant stress - insect performance hypothesis:  quality of plants as food may increase when plants are under stress -->  leads to increase in insect population -->  K decreases when plants recover -->  insect population crashes

REQUIRED READING: Krebs Chapter 14

11. COMMUNITY PROPERTIES

I. What is a community?

A. Definition: assemblage of species occuring in the same area, usually of a specific taxonomic or functional group

B. Is the community a natural unit of organization?

1. Clements: super-organism hypothesis

2. Gleason-Whittaker: individualistic hypothesis

3. evidence on the nature of communities

II. Species diversity

A. Species richness (S) - usefulness of species-area curves

B. Heterogeneity - Shannon-Wiener index H' = - S p_i ln p_i

C. Evenness E = H'/H'_max

III. Species-abundance distributions

A. Preston's log normal distribution

B. Examples

REQUIRED READINGS: Krebs Chapter 20, Appendix IV

Literature:

Root, R. B. 1973. Organization of a plant-arthropod association in simple and diverse habitats: the fauna of collards. Ecological Monographs 43:95-124.

Whittaker, R. H. 1975. Communities and Ecosystems, 2nd edition. MacMillan Publishing Company, New York.

12. SUCCESSION

I. Successional patterns

A. Primary vs. secondary succession

1. primary succession: occurs on new substrate (e.g., glacial substrate, sand dunes)

2. secondary succession: occurs after disturbance of an existing community (e.g., abandoned farmland, after fire)

B. Community parameters that change with succession

1. biomass/standing crop

2. plant productivity

3. species diversity

4. rate of change in species composition

C. Climax communities

1. monoclimax

2. polyclimax

3. climax-pattern hypothesis

4. no climax

II. Theories of succession

A. Connell and Slatyer's (1977) 3 models of succession

1. facilitation model

2. inhibition model

3. tolerance model

B. Evidence for the 3 succession models

1. facilitation: primary succession on glacial substrates in Glacier Bay, AK

2. tolerance: short-leaf pine in Carolinas (READ section in text)

3. inhibition: Sousa (1979) - experimental test with marine algae

4. different models for different parts of the same successional sequence

a. succession on sand dunes

REQUIRED READING: Krebs, Chapter 21

Literature:

Bach, C. E. 1994. Effects of a specialist herbivore on Salix cordata and sand dune succession. Ecological Monographs 64:432-445.

Connell, J. H. and R. O. Slatyer. 1977. Mechanisms of succession in natural communities and their role in community stability and organization. American Naturalist 111:1119-1144.

Drury, W. H. and I. C. T. Nisbet. 1973. Succession. J. Arnold Arboretum 54:331-368.

Harris, L. G., A. W. Ebeling, D. R. Laur, and R. J. Rowley. 1984. Community recovery after storm damage: a case of facilitation in primary succession. Science 224:1336-1338.

Hibbs, D. E. 1983. Forty years of forest succession in Central New England. Ecology 64:1394-1401.

Sousa, W. P. 1979. Experimental investigations of disturbance and ecological succession in a rocky intertidal algal community. Ecological Monographs 49:227-254.

13. REGULATION OF SPECIES DIVERSITY WITHIN HABITATS

I. Competition

A. competition for resources - n limiting resources required for n species to coexist

B. transitive vs intransitive competition (hierarchy vs network of competitive ability)

C. diffuse competition

D. indirect effects

II. Interactions among trophic levels

A. competition-predation (predators reduce intensity of competition by reducing densities)

1. keystone species

2. specialist predators can reduce species diversity

3. size-efficiency hypothesis / size-selective predation in lakes

B. herbivores and plants

C. conclusions on effects of predators on diversity

III. The role of disturbance in regulating diversity

A. Disturbance

1. removal of biomass

2. impact depends on scale of disturbance relative to size of organisms

B. gap dynamics:  e.g., Sale's (1977) lottery model

C. Intermediate disturbance hypothesis (Connell 1978, Huston 1979)

1. after disturbance, colonization increases, but is followed by competitive exclusion

2. highest diversity at intermediate times since disturbance, and in communities that are disturbed at intermediate levels

3. experimental test: Sousa 1979

IV. Non-equilibrium explanations for coexistence of species

A. Competitive reversals: environment changes frequently; alternately favoring different species

B. Competitive equivalence: rate of competitive exclusion is too slow for outcome to be observed

C. Discontinuous competition: resources limiting only periodically, so competition is intermittent

V. Regulation of between-habitat diversity

A. Latitudinal gradients in species diversity

B. Hypotheses explaining greater diversity in the tropics

1. ecological and evolutionary time

2. climatic stability

3. productivity

4. competition

5. spatial heterogeneity

6. predation

C. Problems in testing theories: circularity and the ability to conduct experiments

REQUIRED READINGS: Krebs Chapters 23 (in part), 24

14. ISLAND BIOGEOGRAPHY

I. Islands

A. Geographic islands

B. Habitat islands

II. Dynamic equilibrium theory of island biogeography (MacArthur and Wilson 1967)

A. Immigration curve: immigration rate decreases as the number of species already on an island increases

B. Extinction curve: extinction rate increases as the number of species already on an island increases

C. Equilibrium number of species occurs when immigration rate = extinction rate, but with a continual turnover of species

D. Factors affecting the equilibrium number of species

1. island area

a. higher extinction rates on smaller islands

b. model predicts increase in number of species with increase in island area

c. importance of habitat diversity

2. distance to mainland

a. higher immigration rates on closer islands

b. model predicts decrease in number of species with increase in island remoteness

E. Experimental approaches to test model

1. Simberloff and Wilson (1969) - experimental defaunation of mangrove islands

REQUIRED READING: Krebs Chapter 24 (in part)

Literature (Diversity):

Connell, J. H. 1978. Diversity in tropical rain forests and coral reefs. Science 199:1302-1310.

Huston, M. 1979. A general hypothesis of species diversity. American Naturalist 113:81-101.

Inouye, D. W. 1977. Species structure of bumblebee communities in North America and Europe. Pages 35-40 in W. Mattson, ed. The role of arthropods in forest ecosystems. Springer-Verlag, NY.

Paine, R. T. 1966. Food web complexity and species diversity. American Naturalist 100:65-75.

Pianka, E. R. 1966. Latitudinal gradients in species diversity: a review of concepts. American Naturalist 100:33-46.

Literature (Island biogeography):

MacArthur, R. H. and E. O. Wilson. 1969. The theory of island biogeography. Princeton University Press.

Simberloff, D. S. and E. O. Wilson. 1969. Experimental zoogeography of islands: the colonization of empty islands. Ecology 50:278-296.

Simberloff, D. S. 1976. Experimental zoogeography of islands: effects of island size. Ecology 57:629-648.

15. COMMUNITY METABOLISM: PRIMARY PRODUCTIVITY & NUTRIENT CYCLING

I. Definitions

A. Autotrophs (producers) - organisms that can synthesize necessary organic molecules from inorganic sources (plants, algae, some bacteria)

B. Heterotrophs (consumers) - organisms that must obtain organic molecules from other organisms (animals, fungi, many unicellular organisms)

C. Standing crop or biomass = mass of organisms per unit area (units - e.g., tons/hectare; joules/square meter)

II. Primary productivity

A. Types of primary productivity

1. gross primary productivity (GPP) = total rate of energy fixation by photosynthesis (g. C fixed/area/time)

2. net primary productivity (NPP) = GPP - respiration rate

B. Measuring primary productivity

1. Terrestrial systems

a. estimate difference in standing crop over a time interval

b. problems

- hard to account for loss of biomass through death, consumption

- hard to estimate below-ground biomass

- seasonal changes

2. aquatic systems: measure product of photosynthesis (O₂)

a. light bottle: NPP (photosynthesis - respiration)

b. dark bottle: respirational losses (can be used to calculate GPP)

3. NPP efficiency

a. percentage of sunlight energy available for use by next trophic level up

b. GPP efficiency is 1-4%; NPP efficiency <1%

C. Patterns of primary productivity

1. global trends in primary productivity

a. terrestrial vs. aquatic

b. coastal vs. open ocean

c. effects of upwellings of deep water

b. latitudinal patterns

2. factors limiting primary productivity

a. light

b. nutrients (nitrates, phosphates, iron, etc.)

c. water

d. temperature

e. length of growing season

III. Nutrient cycling in a northern hardwood forest ecosystem (Hubbard Brook)

A. Importance of nutrient cycling vs. inputs and outputs of nutrients in an undisturbed ecosystem

1. most nutrients are held in biomass and very tightly recycled; little loss from system

2. output > input for most nutrients except N; nitrogen increased in the system through precipitation and nitrogen fixation by microorganisms

3. half the annual sulfur input was from pollution from burning fossil fuels

B. Effects of deforestation on nutrient cycling

1. greater streamflow caused by reduced transpiration in the deforested watershed

2. export of dissolved inorganic nutrients 13X normal system

a. greater leaching and weathering of rocks and soil

b. uncoupling of the decomposition process from the plant uptake process

c. increase in nitrification and ammonification

3. other changes

4. longer-term consequences

a. algal blooms - eutrophication

b. recovery after vegetative regrowth allowed

c. what if trees had been removed?

d. what if the expt. had been done in a tropical forest?

REQUIRED READING: Krebs Chapter 25, Chapter 27 (in part)

16. THE CARBON CYCLE & GLOBAL CHANGE

I. The Carbon Cycle

A. primarily involves cycling of CO₂

1. between atmosphere and oceans

2. between atmosphere and terrestrial vegetation

B. additional temporal patterns in cycling

1. seasonal fluctuations: atmospheric CO₂ decreases during northern hemisphere growing season

2. long-term increase due to burning of fossil fuels, destruction of terrestrial vegetation

a. unclear where all this CO₂ is going

b. unknown sink for carbon may be increased growth of terrestrial vegetation

C. Intrinsic vs. extrinsic regulation of populations

1. intrinsic regulation = self-regulation

II. Effects of elevated CO₂

A. greenhouse effect:

1. retention of re-radiated long-wave radiation by CO₂ and other greenhouse gases

2. prediction of global warming as a consequence supported by historical record, but causality is arguable

B. range of biological responses to elevated CO₂, global warming

1. individual plants

a. increased growth (e.g., C₃ plants)

b. no change in growth (e.g., C₄ plants)

c. effects on reproduction not well-investigated - could go either way

d. likely to be an upper limit on growth responses to elevated CO₂, as other resources become limiting

2. plant communities - consequences unclear: poorly studied, difficult to perform appropriate and meaningful experiments

3. animals (herbivores)

a. likely to show an indirect response (i.e., respond to changes in plants)

b. N-concentrations in plants likely to decrease

i. insect consumption rates may increase in order to satisfy N-requirements, causing more damage to plants

ii. insect survival and reproductive rates may decline, even with increased consumption rates

4. species distributions

a. if distributions depend on climate (e.g., forest tree species?), changes in climate should lead to changes in distribution of suitable habitat

b. organisms must be able to migrate at rates at least equivalent to the rate at which climatic changes occur

c. different species have differential abilities to migrate

d. organisms face the additional problem of migrating across a fragmented landscape

e. difficult to predict how individual species will respond to changes in both their physical and biotic environments

REQUIRED READINGS: Krebs Chapt. 27 (in part)

17. CONSERVATION BIOLOGY & The Design of Nature Preserves

I. Rarity and the probability of extinction

A. there are lots of ways to be rare

B. factors that affect the probability that a population will become extinct

1. demographic stochasticity: random fluctuations in birth & death rates

2. genetic stochasticity: random fluctuations in the genetic makeup of a population

3. environmental stochasticity: random fluctuations of weather, other abiotic or biotic factors

4. natural catastrophe

5. deterministic extinction: destruction of habitat leads to loss of species that depend on the habitat

6. fragmentation of habitat

C. demographic extinction model: the probability a population will go extinct depends on:

1. population growth rate (r): low r à poor ability to recover from small pop. Sizes

2. variance of growth rate (V): high variance à high probability that r will become negative

3. maximum population size à effects of r and V are exacerbated

II. Effects of framentation on populations

A. direct reduction in area of habitat leads to reduced population size

B. smaller populations more subject to chance extinction

C. smaller populations less likely to maintain genetic diversity

D. reduction in area exacerbated by edge effects

E. recolonization after local extinction inhibited by decreased connectivity with other patches

III. Designing nature preserves to maximize persistence of populations

A. SLOSS debate: Single Large or Several Small preserves?

1. Single large

a. Advantages:

i. minimizes edge:interior ratio

ii. supports larger population

iii. lower turnover rate of species (cf. island biogeography theory)

iv. more habitat diversity

b. Disadvantage: single catastrophe can wipe out entire population

2. Several small

a. Disadvantages

i. high edge:interior ratio means less effective habitat

ii. higher turnover rates

iii. smaller populations more susceptible to local extinction

b. Advantages

i. provides potential for migration among patches (metapopulation)

ii. decreased risk of losing the entire (meta)population due to catastrophe

B. Corridors

a. Advantages: increased potential for migration

b. Disadvantages

i. increased chance of disease, fire spreading throughout (meta)population

ii. physical corridors vs. effective corridors

REQUIRED READING: Krebs Chapter 19 (in part)