Ecology Exam II

Three main categories affecting decomposition rates

Litter quality

Climate

Decomposer Organisms

Litterbag experiments

Measure decomposition rates by putting mesh bag of litter in environment. Mesh size is important and you must standardize lost litter measurements

Decomposition rates

Impacted the most by temperature and moisture, but also oxygen availbility, litter quality, and organisms

Potential Evapotranspiration

Water that could leave if water were readily available; theoretical

Actual Evapotranspiration

Water actually lost through evaporation and transpiration; experimental

Aerobic Decomposition

With oxygen

Form of respiration; redox reaction. Oxygen is a “conveyor belt” for electrons

Anaerobic Decomposition

Without oxygen

Fermentation followed by methanogenesis
More complex than aerobic decomposition and involves multiple organisms and chemical reactions

Anoxic Decomposition

Microorganisms utilize chemically bound oxygen to break down matter; “steals oxygen”

Ex: Using SO4 to break down organic matter by turning it into S, H2O and CO2

Litter Quality

Higher quality litter has more N per C, and less lignin. Lower quality has more lignin and less N per C

Lignin

More structured than cellulose, therefore harder for microorganisms to break down

Life History

A collection of age or stage specific traits directly affecting reproductive success (fitness)

Constraints

Physical limitations to the possible types of life history that a species can have

Principle of Allocation

Describes how any energy used for one function reduces the amount available for another function (trade-offs)

Fitness

Evolutionary success of individuals in a certain environment so that they survive and reproduce better than other individuals
Genetic contribution to future generations

What kind of offspring does natural selection prefer?

Larger/more offspring
Larger offspring survive better than smaller
More offspring ensures passing genes along

Semelparous

Only one reproductive event in a lifetime; pushes reproduction to its maximum biotic potential

Iteoparous

pattern of repeated reproduction throughout lifetime

Fecundity

Maximum potential capacity to reproduce

What is the evolutionary advantage to living past reproductive age?

Taking care of offspring increases fitness

Senescene

Gradual breakdown with age of body, and subsequent increase in mortality

Does asexual reproduction age?

No, with reproduction by fission, aging does not evolve. If senescence did occur, all individuals would age and die and the population would go extinct

How are age of reproduction and lifespan related?

Delaying onset of reproduction can increase active lifespan, it decreases aging

Where/when does conditioning take place?

Fungi, bacteria, mites etc colonize highly fragmented litter previously broken up by shredders. This makes the detritus more appealing for the remaining decomposers; adding “peanut butter” to the cracker.

Steps of Decomposition in Freshwater

1. Leaf litter adds organic matter into the stream

2. Microbes: fungi and bacteria condition (colonize) the leaves

3. Fragmentation: shredders and water current break up the leaves

4. Collectors: consumers use the remaining fine particles

What do shredders break down?

Coarse litter. First step of decomposition

Who comes second in decomposition process?

Fungi and bacteria (and mites and nematodes) condition/colonize the leaves, adding “peanut butter” to the detritus

Static Life Table

Follows individuals in one age group assuming population age structure and age-related mortality and fecundity are NOT changing over time

Dynamic Life Table

Follows cohort of individuals from birth to death; more accurate than static but more difficult

Steps for Every Population Problem

1. Describe reproduction and resource limitation

2. Choose the tool that answers the question

3. Calculate with units and interpret biologically

4. Check whether the assumptions fit

What is R₀ in a life table?

Net reproductive rate; Sum of all lxmx = {ans} daughters per newborn female

What does it mean if R₀ > 1?

More daughters are born than females in the original cohort

What does it mean if R₀ < 1?

Fewer daughters are born

What is lx?

Survivorship for x age class

What is mx?

Fecundity for x age class

What is T in relation to life tables?

The sum of xlxMx divided by lxMx;

What is r?

Instantaneous growth rate

intrinsic per capita growth rate in a logistic model

r-selected species

• Rapid development

• Early reproduction

• Small body size

• Many offspring

• Density independent

• Cycle of booms (peaks) and busts (lows)

• Limited by reproductive rate (r)

K-selected species

• Slow development

• Delayed reproduction

• Large body size

• Few offspring

• Density dependent

• Relatively stable

• Limited by carrying capacity (K)

Ruderal species (Grimes classification)

High relative growth rate, short-lived leaves, and short-statured plants. Allocates resources mainly to seed reproduction. high disturbance, low stress

Grimes Plant Life History Classification

Categorizes plants into three primary strategies: competitive, stress-tolerant, and ruderal

Competitive Plants (Grimes classification)

Do well in high competition, low disturbance; birch tree

Winemiller Rose Classification

Categorizes life history strategies by fecundity, juvenile survivorship, and age of reproductive maturity

Three questions for every model

Time: Are changes represented in steps or continuously?

Density: Does per capita growth (r) depend on N (population size)?

Boundaries: Can organisms enter or leave? (Closed system? Immigration/Emigration?)

Characteristics of Geometric Growth Model

Equal intervals

Discrete growth (time steps)

Constant net change over the interval (λ)

No limit to growth (density independent), closed system

Characteristics of Exponential Growth Model

Growth is continuous over time

When r is constant, larger N produces larger net change

dN/dT is “how quickly the population is changing now”

No limit to growth and closed system

Does r impact N in an exponential growth model?

No, r (per capita growth rate) remains constant and independent of N

Stochaschity

random variation that makes population growth less predictable

Environmental stochasticity

Unpredictable changes in the environment affect many individuals. can affect both large and small populations