General Ecology - Exam One

What is ecology?

Study of the environment; scientifically, the study of interactions among organisms in an environment; interdisciplinary (biology, genetics, evolution, phys. sciences, earth sciences, social sciences)

Not environmentalism → not a moral stance

Scales of ecology

Individual ←→ pop. ←→ community ←→ ecosystem ←→ biosphere; all impact each other; hierarchical

Spatial scale → globe to bacteria (m) (the amount of space in which something occurs)

Temporal scale → glacial retreats to bat echolocation (days) (the amount of time in which something occurs)

Climate vs weather

Weather → day-to-day variation (in temp., rainfall, humidity, etc.)

Climate → longterm average description of weather

Why do we care about climate?

Impacts species distribution and abundance → differs according to species (Rufous crowned vs House sparrows); species dist. are related to constraints imposed by the env.

Climate - what do we mean?

Averages, extremes (heat and coral reefs, drought and borer beetles), variability, timing

All impact species distribution and abundance; a matter of which of these factors are doing what

Why does climate vary across the earth?

Bands of wet and dry (Hadley Cells), uneven solar input, tilt and orbit of the earth, winds and Earth’s rotation (Coriolis Effect), topography, ocean currents

Hadley Cells

Large-scale atmospheric convection cells in which air rises at the equator and sinks at medium latitudes

How?

• Intense solar heating at the equator → air expands and rises as it warms → rising cools it down, forming clouds → cold air holds less moisture → moisture falls as rain → more air rises → dry air is pushed towards the poles → gets denser; sinks → dry bands created → warm air picks up moisture and rises → completes the cycle

Solar radiation

Ultimate source of energy that drives global climate

Uneven input from the sun → at the equator, solar radiation is concentrated over a small area (warmer); in the northern hemisphere, solar radiation is concentrated over a larger area (cooler)

Tilt and orbit of the earth

Creates the seasons → different in northern vs. southern hemis.; no season at the equator (wet and dry seasons, but no actual change in day/night length)

Coriolis Effect

Differences in velocity mean that as air or water moves over Earth’s surface, their trajectories appear to be deflected (moving faster at the equator; think of throwing a ball from Costa Rica to Anchorage → it’ll end up in front of them)

Topography

Going up a mountain = colder temperature and more rain

Rainshadow → the dry area on the leeward side of a mountain (opposite of wind’s direction); air warms and travels up the mountain, cools to form clouds, drops moisture on wayward side, dry by the time it reaches the leeward side → creates a wetter climate on one side, and a dryer climate on the other

Ocean Currents

Move the cold and warm water around

Biomes

Based on the growth form of the dominant vegetation; a combination of precipitation and temperature; line up with the bands of wet and dry

Examples:

• Tropical rainforest → diverse; temp. doesn’t really change; precip. can change (but there’s lots of it)

• Tropical dry/seasonal forest → temp. consistent; more severe dry seasons (trees will drop leaves)

• Temperate grassland → big swings in temp. and precip.

• Temperate seasonal/deciduous forest → big swings in both (but lots of rain)

• Temperate evergreen → huge amounts of rain; little bit of seasonal temp.

• Deserts (hot or cold) → very little rainfall; temp. fluctuations

• Boreal forest → huge swings in temp.; decent amt. rainfall

• Tundra → basically freezing year round

Physiological tolerance

Limits on environmental conditions that an organism can tolerate (Rufous crowned vs. House sparrow)

Tolerance and species ranges

Tolerance defines species ranges

There’s an optimum (of many factors and conditions) that a species can do its best in → differs between species

• Lizards → temp. and sprint speeds (Goldilocks zone)

• Dr. Janzen → tropical species have a limited range of temperatures they can handle; nontropical species can typically tolerate a wider range

Environmental stress strategies

Avoidance - migratory birds; ephemeral annuals; hibernators

Tolerate - polar fishes; succulents

Shifts in species ranges

Some species track changes in temp. and precip. → Grinnel Resurvey Project (84% of birds change their ranges across 100 years)

Evolution

Before genetics: a change in distribution of a pop. from one generation to the next; pop.-level shift in trait dist.

Now: change in allele frequencies

Can happen rapidly (native anole lizards and arboreal traits)

Mechanisms of evolution

Natural Selection

Gene flow

Genetic drift

Mutation

Natural Selection

The process by which individuals with certain heritable characteristics survive and reproduce better than individuals with other heritable characteristics

Non-random

Tenets of evolution by natural selection

1. Individuals vary in their traits

2. Traits are inherited from their parents

3. Individuals with certain traits are better at surviving and reproducing than individuals with other traits

Types of natural selection

Directional selection

Stabilizing selection

Disruptive selection

Directional selection

Changes the average value of a trait (a small or large trait is favored) → e.g., Darwin’s finches

Effect on heterozygosity depends

Stabilizing selection

Central trait value is favored; no change in the average trait value over time (selection against the extremes) → e.g., human birth rate (lower weight = hard to maintain body heat; higher weight = birth complications)

Decreases heterozygosity

Disruptive selection

Extremes are favored; no change in the average trait value over time (selection against the middle); can lead to reproductive isolation and thus speciation → e.g., seedcracker finches (finches with larger mandibles could handle hard seeds; finches with smaller mandibles could handle soft seeds; finches in the middle were the masters of none)

Increases heterozygosity

Genetic Drift

Due to chance; random with respect to fitness (survival and reproduction); greater in small populations

• In small populations, the loss of alleles and fixation of alleles can lead to an increased frequency of harmful alleles → shrimp-spined wolves; prairie chickens

• E.g., a landslide randomly wipes out the majority of a population → bottleneck; drastically reduces the size of a population

Decreases heterozygosity

Gene flow

The movement of alleles between populations; can introduce new alleles to a population; can make different populations with gene flow resemble each other

• E.g., hatchery fish (wild x captive caught spices up diversity [new population resembles both parent pops.])

Increases heterozygosity

Mutation

A change in the DNA of a gene; ultimate source of genetic variation; leads to the formation of new alleles (beneficial [or otherwise])

Increases heterozygosity

Genetic diversity

The total number of genetic characteristics within a pop.; influences the ability of a population or species to respond to changes in the environment (higher g.d. = greater ability to respond)

Founder event

When a small number of individuals set out from an ancestral population to establish a new, isolated colony (new colony only has a fraction of the g.d. of old colony)

Foraging

How organisms select, search for, and consume food within their natural environment

Foraging - costs and benefits

Costs - decrease fitness → often energetic or predation risk

Benefits - increase fitness for survival and repro. (finding the energy required to grow or be reproductively active)

Organisms must find the balance

Optimal foraging theory

Evolution has favored behaviors that maximize an individual’s rate of food harvest and/or while minimizing costs

Prediction: If organisms are foraging optimally, they’re going to maximize the net benefit while minimizing costs

Predators change the costs (not benefits); changes in food resources change the benefits (not costs)

Max benefit: closest, highest peak

Costs: increase linearly

B=C → max distance an organism should forage away from the den before costs outweigh benefits

OFT - diet choices

Energy content = E (1 or 2)

Handling time - time it takes to process one prey item (h)

Profitability - energy gained per unit of time (E/h)

Critical search time

((E1 • h2)/E2) - h1

Compare to the search time of the preferred prey item

• If > CST, organism should invest in a mixed diet

• If < CST, organism should only eat preferred prey

Factors such as time of day, temperature, season, etc. can impact all of the above

Social behavior

Any direct interaction among a group of individuals of the same species that is organized in a cooperative manner—extending beyond sexual and parental care

Costs and benefits of group living

As group size increases, more competition within group; as group size decreases, more competition between groups (and a higher risk of predation)

Must find optimal group size

Evolution of cooperation

• Mutual benefit

• Reciprocity

• Kin selection

• Delayed direct fitness benefits

• Cooperative breeding

Mutual benefit

Defense against predators; protection; acquisition of resources (food, shelter, etc.)

• Schools of fish, nesting colonies of seabirds (predation risk lowered)

• African wild dogs

• Birds (larger the group, the fewer head jerks [more time to eat]; as flock gets bigger, handling time decreases)

  • BUT, the bigger the group, the quicker resources are depleted and the more often they have to move to look for food

Costs → dilution of resources, predator attraction, increase in parasites/pathogens, cheating (on effort)

Reciprocity

If you scratch my back, I’ll scratch yours

• Allogrooming

• Vampire bats and sharing food (more likely to share with those who shared before)

• They must be able to recognize each other; must be able to remember who helped them before

Kin selection

Between related individuals; individuals will gain direct and indirect fitness benefits by helping

• Direct fitness benefit → fitness through one’s own reproduction

• Indirect fitness benefit → fitness through helping kin

• Inclusive fitness → sum of direct and indirect fitness

• Coefficient of relatedness (r ) → proportion of an individual’s total genotype that is identical to another due to shared ancestry

  • 50% for mother, father, sibs → r = 0.5

  • 25% for grandparents, nieces → r = 0.25

  • 12.5% for cousins → r = 0.125

  • Unrelated individuals → r = 0

  • Identical twin → r = 1.0

Hamilton’s Rule

Equation to decide whether cooperation occurs due to kin selection

• r = B - C > 0

  • r = coefficient of relatedness

  • B = benefit to the recipient (usually # offspring/dominant male - # offspring/solo male)

  • C = cost to the actor (usually # offspring/solo male - # offspring/subordinate male)

  • If r > 0, net positive; kin selection occurring

  • If r < 0, net cost; kin selection not occurring

Delayed direct fitness benefits

Gain direct fitness benefits later on → common in lekking groups (learning to attract mates); manakins (Michael Jackson birds)

Cooperative breeding

Helping raise others’ young → extreme helping (helping 💯)

Sexual selection

Differential reproductive success due to variation among individuals and success at getting mates → might result in survival deficit (but, hey, at least they had sex)

• Male and female differences → females get to be choosier (an egg is a lot more energetically expensive than sperm)

• Skewed mating success → a few males might get most of the matings

  • Lekking species → 80% of the matings go to a few males

• Two forms: intrasexual and intersexual

Intrasexual selection

Male - male competition; fighting within the same sex; leads to the development of exaggerated weapons (antlers, horns, tusks, claws, songs)

Intersexual selection

One sex (usually female) chooses a mate from among members of the opposite; leads to the development of exaggerated ornaments or dances

• Direct benefits → parental care, resources, protection

• Indirect benefits → good genes, sexy sons (sons who are more likely to find mates and thus spread genes)

  • Peacocks → males with more eyespots have more matings and a better immune system; bigger eyespots = higher probability that the offspring will survive

Alternative reproduction strategies

• Sneaker males → rush in and release sperm on females’ eggs

• Satellite males → help males

• Males that look like females

When sexual and natural selection are at odds with each other

What’s good for the ladies might not be what’s best for, you know, living

Ravens

Populations have increased by 300%; ravens are generalists → can take advantage of human infrastructure; can regularly impact species of concern (can push small, isolated groups to extinction; anthropogenic features mean there’s no limitation of prey abundance)

Managed by

• Lethal removal, egg removal, nest removal, resource management

  • BUT native species; Migratory Bird Act

Habitat selection

The process by which an organism chooses specific environmental patches/living areas based on factors that influence its survival and repro. rates

• Space use - how organisms distribute themselves, move, and utilize the physical areas within their environments

Life histories

How and why organisms survive and reproduce in different ways → strategy of the major events in an organism’s life

Examples

• Size and # of offspring

• Body size

• Specialization (vs. being a generalist)

• Age of maturity

• Size at maturity

• Lifespan

Life history schedules

Different for each species

• Black rhino (K-selected): “If I can survive until next year, I can reproduce again.”

  • Slow pace of life → steady, predictable environments

  • Long lifespan

  • Reproduce at long intervals; long gestation

  • 1 offspring/pregnancy

  • Investing in growth for future fecundity

• House mouse (r-selected): “I probably won’t live until next year, anyway. Live hard, die hard.”

  • Fast pace of life → variable, unpredictable environments

  • Short life spans

  • Short reproduction interval; short gestation

  • Lots of offspring/pregnancy

  • Investing in immediate reproduction

How many young should an organism have?

Lack’s hypothesis: Clutch size is determined by the max # of offspring an organism can feed

• As clutch size increases, the probability of each offspring surviving decreases (becomes a curve)

• Parental cost → bigger broods decreased survival and reproduction of the parents (it takes a lot of energy)

  • Those with smaller broods probably don’t have a lot of energy to go around

Reproductive decisions

• Timing of breeding

• # offspring/attempt

• # young/year

• Amt. of parental care → early growth period = critical for later survival

Everything’s a tradeoff

Allocating limited energy to growth and reproduction in a way that’s efficient within evolutionary and environmental constraints

Classifying life histories

r-selected species: high population growth rate, not very strongly competitive, rapid development, small, fast maturation, semelparitous (single) reproduction, lots of (small) young

K-selected species: low population growth rate, high competitive ability, slow development, large, slow maturation, iteroparous (many) reproductions, few (large) young

Life history traits

Fast-slow gradient → spectrum of ways organisms live their lives

• Slow-fast life history continuum → resource availability, unpredictability of an environment (variability)

  • Fast life histories in the temperate zone

Competitive - Stress - Ruderal (Grime’s) Triangle

Trade-off examples

Migration → better environment, but lots of energy

Being flashy → better chances at repro., but also of predation

Offspring # vs. size

Current reproduction vs. future reproduction/survival

Higher reproductive effort is correlated with higher mortality

• Greater costs for “poorer quality” individuals: how good is the organism at surviving and reproducing (more likely to be affected by other trade-offs)?

• Greater costs following harsher winters → resources are not always limiting for all individuals or in all conditions (rich = cheating at life)

Conservation implications

Reproduction will vary more than survival for slow life histories (often trade off repro. outlet for survival)

• Ducks → when habitat was better, females had higher natural mortality (more energy towards repro.; more likely to die) → reproduction has become more costly for adult females

  • Is managing for repro. still the most effective management strategy—even if ducks have a slow life history?

Population ecology

What influences where species are found?

• Density

• Abundance

Population

A group of interacting individuals of one species living in a specific area

• Interacting = reproducing sexually → group of interbreeding individuals; reproducing asexually; other kinds of interactions (competition, etc.)

Characteristics of populations

Size, density, age structure, sex ratio, genetic structure, dispersion

Size → # individuals in an area

Density → # of individuals per unit area (pop. size/habitat size)

How to determine size and density?

• Count them all (geographically restricted populations [e.g., island])

• Sample populations

  • Area-based count

  • Distance sampling

  • Mark-recapture

Population abundance

Relative representation of a species in a particular area; measured via population sampling methods

Area-based count

Quadrats → counting # individuals in a given area or volume

• For organisms that don’t move much and can be counted accurately

• Assumption: area is representative of the entire population you’re sampling

Distance sampling

Measurements of distance from a point/straight line

• For organisms that move a lot and can be counted accurately → birds, etc.

Mark-recapture methods

Capture, mark with individual bands, release, recapture (at a different point in time)

• For organisms that are mobile that you can capture and recapture → organisms that are hard to detect (nocturnal, etc.)

Simple population growth models

r = b • d

• r = estimated annual pop. growth rate

• b = per capita birth rate

• d = per capita death rate

b > d → pop. increasing

b < d → pop. decreasing

b = d → pop. stable

Simple population growth models cont.

r = b • d / t • Navg.

• t = time

• Navg. = avg. pop. size over period of time (average of two [or more] pop. sizes provided)

Simple population growth models assume that b and d are consistent over time (closed pop. → no migration, etc.)

• Immigration → movement into pop. → increase abundance

• Emigration → movement out of pop. → decrease abundance

Age structure

Proportion of pop. within each age class; whether pops. are increasing or decreasing → not every age class dies or reproduces at the same rate

Abundance is good, but not always sufficient → loggerhead sea turtle example; turtles don’t start reproducing until adulthood (takes a long time); large juveniles were the most important stage (not eggs)

Life tables

Display how survival and reproduction vary with age, size, or the life cycle stage; 2 types:

• Static

• Cohort

Static life tables

Calculate age-specific survival and fecundity at one period in time

Cohort life tables

Follow individuals from birth to death (dynamic); work great for short-lived species

• Cohort - group of individuals born at the same time

Life table variables

Nx → age group

lx → survivorship (proportion of individuals that survive from birth - given time [x]) → Nx/N0 (starting pop.)

qx → mortality rate (how many are dying between age classes)

• 1 - (Nx+1/Nx) → Nx+1 = next age class down from age of interest (Nx) → nothing fancy; don’t panic

Fx → fecundity (total fecundity of entire pop. at age x)

Mx → per capita fecundity → per-female fecundity for age class x → Fx/Nx

lx • mx → survivorship • fecundity → R0 → net reproductive rate per generation

• How many offspring each female has

• R0 > 1 → pop. increasing

• R0 < 1 → pop. decreasing

• R0 = 1 → pop. stable

T → generation time → (sum of x • lx • mx column [age • lxmx])/R0

r vs. R0

r is relative to 0; R0 is relative to 1

• r = ln (R0)/T

Population growth models

Geometric

Exponential

Logistic

Geometric growth

Populations are increasing; unlimited resources; discrete time intervals

• Pops. reproduce in synchrony (at discrete times)

• Pops. grow by constant proportions; not limited in growth → algae, invasive species, disturbed environments

Lambda → annual rate of change → N(t+1)/N(t)

• > 1 → pop. increase

• < 1 → pop. decrease

• = 1 → pop. stable

• Can predict pop. size in future:

  • Nt = Lambda^t • N0

Exponential growth

For species that reproduce at all different times (continuous reproduction), but pops. still change by constant proportions and are unlimited in their growth

dN/dt (slope) → change in pop. over time

• dN/dt = rN (intrinsic growth rate • pop.)

• Predict future pop. size

  • Nt = N0e^rt

    • N0 = starting pop size

    • r = intrinsic growth rate

    • t = time

Logistic growth

Populations cannot continue unlimited growth forever → pops. grow until K (carrying capacity) is reached

• K = max # of individuals that an environment will sustainably support

• dN/dt = rN(1 - N/K)

What drives logistic growth and influences pop. size?

Density dependence

Density independence

Density dependence

Initial rates change as a function of the density of a pop.

• Disease, food, light, space

• Negative density dependence → logistic growth patterns (pop. growth decreases as density increases)

• Positive density dependence → Allee effects (pop growth decreases and density decreases [pack hunters, etc.])

More regular fluctuations around K

Density independence

Vital rates are not a function of pop. density

• Fires, pollution, floods, severe weather (not caused by the # of individuals)

Larger, more severe and sudden fluctuations around K

Type I survivors

Low mortality at young age; higher mortality at the end of life (old age); K - selected species → humans, slow species, most larger mammals

Type II survivors

Mortality rate constant throughout life (linear) → birds, lizards, small mammals

Type III survivors

Higher mortality at younger ages (very low chances of survival); mortality rate decreases as age goes on → faster species; r-selected species; invertebrates

Survivorship curves and extinct species

Aged (at time of death) fossils and survivorship curves can help us understand the lifestyle of extinct species

Population dynamics

The ways in which populations change in abundance over time

• Annual K is rarely constant → changes based on resources

Fluctuations are the rule

Variation in the density of a population; can be influenced by how much the environment fluctuates (tropics vs. temperate) and the inherent stability of a population (slower species vs. faster species)

Irregular fluctuations

• Stochasticity → random events

Periodic fluctuations

• Delayed density dependence → population performance reflects density in previous years → species responding to what happened in the past

  • Time lags → delays in response of birth and death rates to changes in the environment

Delayed density dependence and logistic growth

Time lags and DDD → dN/dt = rN (1-N(t-†)/K)

• † = time lag

Overshooting K and then plummeting below K (degraded K) is common

Extinction risk and variable growth

Greater variability → more likely to go extinct (> variability in lambda > extinction)

Ecological Traps

When an individual mistakenly thinks that a bad quality habitat is good quality habitat → environments are falsely attractive → mayflies

• Can be used as a management strategy (goats in the Galapagos)

Mismatch in evolutionary cues

Undervalued resources

When an individual mistakenly thinks that good quality habitat is bad quality habitat → environments are falsely unattractive

Mismatch in evolutionary cues