˚˖𓍢ִ໋`🌿:✧˚.📷⋆𖧧 Ecology exam 2 all topics 🐛°‧ 𓆝 𓆟 𓆞 ·｡

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🦚Life history

🪺The schedule of how an organism allocates resources to growth, development, defense and reproduction over its lifetime.

🦚Three key properties of life histories

🪺They are genetically based and heritable, subject to natural selection, and considered to maximize fitness.

🦚Fecundity

🪺The number of offspring produced per reproductive episode.

🦚Parity

🪺The number of reproductive episodes an organism has in its lifetime.

🦚Semelparous

🪺Reproduces only once, then dies (e.g., Pacific salmon).

🦚

🪺Reproduces multiple times during its life (e.g., humans, most birds).

🦚Parental investment

🪺The amount of time and energy parents give to each offspring.

🦚Longevity

🪺The life span (life expectancy) of an organism.

🦚Annual vs. perennial

🪺Annuals live one year; perennials live more than one year.

🦚Principle of allocation

🪺Resources are limited, so energy devoted to one function (growth, defense or reproduction) cannot be used for another. This is why life histories involve trade-offs.

🦚Goldenrod seed graph

🪺Shows a trade-off between offspring number and offspring size: plants that make bigger seeds make fewer of them.

🦚Magpie clutch experiment (Högstedt 1980)

🪺Researchers added or removed eggs. Nests with 7 eggs (the natural average) fledged the most chicks, supporting the idea that natural clutch size maximizes fitness. Too many eggs meant parents couldn't feed them all.

🦚Kestrel brood experiment (Dijkstra et al. 1990)

🪺Adding chicks increased the number fledged but lowered parent survival; removing chicks did the opposite. Shows a trade-off between current reproduction and parent survival (future reproduction).

🦚What the kestrel experiment shows about males vs. females

🪺Females had lower survival than males in every treatment, suggesting they pay a higher cost of reproduction.

🪻Photoperiod

Day length. A reliable cue organisms use to predict seasonal changes, because it changes the same way every year.

🪻Phytochrome

The plant pigment that senses day length by switching between two forms (Pr and Pfr) depending on red vs. far-red light.

🪻Grama grass flowering by latitude

At 47°N it flowers in late summer at 16 hours of daylight; at 30°N it flowers in autumn at 13 hours. Northern plants must flower while days are still long because winter comes earlier.

🪻Daphnia diapause by location

Alaska populations enter diapause at 20 hours of daylight; Michigan populations at 12 hours. Shows heritable, locally adapted cues.

🪻Diapause

A dormant resting state an organism enters to survive unfavorable conditions.

🪻Phenotypic plasticity

The ability of one genotype to produce different phenotypes depending on the environment it experiences.

🪻Frog metamorphosis with high food

Tadpoles grow fast and metamorphose early and large (point A).

🪻Frog metamorphosis with low food

Tadpoles compromise, metamorphosing somewhat later and somewhat smaller (point C), instead of same age but tiny (B) or same size but very late (D).

🪻Trade-off in frog metamorphosis timing

Metamorphosing early means earlier first reproduction; being bigger means better ability to escape predators.

🪻Snails with crayfish predators

Snails delayed first reproduction (about 77 vs. 59 days) and were about twice as big (213 vs. 110 mg), too big for crayfish to crush. Lifetime egg production did not change.

🪻Phenology

The timing of seasonal life history events, such as flowering, leaf-out and migration.

🪻Walden Pond flowering data

Plants now flower earlier than in Thoreau's time; warmer spring temperatures mean earlier flowering.

🪻Phenological mismatch

Species shift timing at different rates (leaf-out about 18 days earlier, insects about 13, birds only about 3), so birds may arrive after the food they need has peaked.

🪻Why birds shift less than plants

Birds time migration partly by day length, which hasn't changed, while plants and insects respond to temperature, which has.

📈Fast (r-selected) life history traits

Many offspring, short life span, fast growth, early reproduction and maturation, small parental investment (e.g., mouse, rabbit).

📈Slow (K-selected) life history traits

Few offspring, long life span, slow growth, delayed reproduction and maturation, large parental investment (e.g., chimp, elephant).

📈Who proposed r vs. K selection?

MacArthur and Wilson, 1967.

📈Where fast life histories do well

Unpredictable or disturbed environments where populations are often below carrying capacity, so fast growth (high r) wins.

📈Where slow life histories do well

Stable, crowded environments near carrying capacity (K), where competitive ability and heavy investment per offspring win.

📈Grime's C-S-R scheme (1974)

Classifies plants and sessile invertebrates by two axes, stress (resource availability) and disturbance, giving three strategies: competitors, stress tolerators and ruderals.

📈Competitors (C)

High resources, low disturbance. Slow growth, late maturity, high energy to asexual reproduction and biomass, low defense, long-lived. Example: goldenrod.

📈Stress tolerators (S)

Low resources, low disturbance. Slow growth, late maturity, high energy to defense, long-lived. Example: woolly lousewort.

📈Ruderals (R)

High disturbance, high resources. Fast growth, early maturity, high energy to sexual reproduction (seeds), short-lived. Example: Canada thistle.

📈Why stress tolerators invest heavily in defense

Resources are scarce, so lost tissue is very costly to replace.

📈Why ruderals put energy into seeds

Disturbance frequently wipes out the site, so they must reproduce fast and disperse to new open patches.

📈Why there's no strategy for low resources plus high disturbance

A plant can't regrow quickly after disturbance when resources are too scarce to support growth.

📈How C-S-R predicts community composition

Resource and disturbance levels predict which strategy dominates: ruderals in disturbed sites, competitors in fertile undisturbed sites, stress tolerators in harsh low-resource sites.

🧮Species richness

The number of species in a community.

🧮Five possible productivity–richness relationships

U-shaped, negative, none, positive and hump-shaped.

🧮Mittelbach et al. 2001

Reviewed many studies and found the hump-shaped productivity–richness relationship was the most common in nearly every group.

🧮Why richness is hump-shaped with productivity

At low productivity few species can survive; at intermediate levels many coexist; at high productivity a few strong competitors take over.

🧮Park Grass Experiment

Started in 1856 at Rothamsted, England. Adding more types of resources (fertilizers) to grassland plots lowered the number of plant species.

🧮Park Grass regression

Species = 34.1 − 3.1 × (number of resources), R² = 0.49, p = 0.02. Each added resource meant about 3 fewer species, and resources explain about half the variation.

🧮MacArthur & MacArthur 1961

Foliage height diversity (number of vertical vegetation layers) predicted bird species diversity better than plant species diversity did.

🧮Why habitat structure increases diversity

More structural layers create more niches, so more species can coexist.

🧮Intermediate Disturbance Hypothesis

Species richness is highest at intermediate (occasional, moderate) disturbance, compared with rare or very frequent disturbance.

🧮IDH: low disturbance

Dominant competitors exclude other species, so richness is low.

🧮IDH: high disturbance

Only a few tough or fast-colonizing species survive, so richness is low.

🧮Lubchenco 1978

🦠Algal species richness in tide pools peaked at intermediate snail (grazer) densities.

🌟🐠Keystone species

A species whose effect on community structure is disproportionate to its abundance.

🌟🐠Paine 1974 sea star experiment

When sea stars (which eat mussels, barnacles, limpets and snails) were removed, mussels monopolized the space and richness crashed from about 18 to 1–2 species.

🌟🐠Why sea stars maintain diversity

They eat the dominant competitor (mussels), which frees up space for other species.

🌟🐠Direct effect

One species affects another through a direct interaction, such as predation.

🌟🐠Indirect effect

One species affects another through an intermediate species.

🌟🐠Density-mediated indirect effect

An indirect effect caused by changing the number (density) of an intermediate species.

🌟🐠Knight et al. 2005 trophic cascade

Fish eat larval dragonflies, so fewer adult dragonflies eat pollinators. Shrubs near ponds with fish got about 3.5 pollinator visits per 20 minutes vs. nearly 0 without fish.

🌟🐠Trophic cascade

Effects of a predator that pass down through multiple trophic levels.

🌟🐠Trait-mediated indirect effect

An indirect effect caused by changing the behavior or traits of an intermediate species.

🌟🐠Beckerman et al. 1997 spider experiment

Grasshoppers alone caused about 58% herbivory. With a lethal spider it dropped to about 17%, and with a nonlethal spider (mouthparts glued) also about 17%, so the effect came from grasshopper behavior, not from being eaten.

🌟🐠Bottom-up control

Abundance is controlled by resources at the bottom of the food chain; more producers mean more at every level above.

🌟🐠Top-down control

Abundance is controlled by predators at the top; effects alternate going down (more top predators, fewer secondary consumers, more primary consumers, fewer producers).

🌟🐠Trophic levels

Producers, primary consumers, secondary consumers and tertiary consumers.

Population spatial structure

The pattern of density and spacing of individuals in a population, shaped by acceptable habitat, biological interactions and dispersal.

Five characteristics of population distributions

Geographic range, abundance, density, dispersion and dispersal.

Geographic range

The total area covered by a population.

Cosmopolitan species

Species with very large geographic ranges that can span continents (e.g., sugar maple).

Endemic species

Species that live in a single or few, often isolated, locations (e.g., American hart's-tongue fern).

Abundance

The total number of individuals in a population within a defined area.

Density

The number of individuals per unit area or volume.

Dispersion

The spacing of individuals relative to one another (clumped, evenly spaced or random).

Dispersal

The movement of individuals from one area to another.

Dispersal vs. migration

Dispersal is a one-way move to a new area; migration is a regular round-trip seasonal movement.

Survey

Estimating population size by sampling part of it instead of counting every individual.

Line intercept method

Measures cover along a line, but not density.

Audubon Christmas Bird Count

An example of a survey that shows relative change in populations over time.

Mark-recapture

Capture and mark individuals, release them, then capture a second sample and count how many are marked to estimate total population size.

Mark-recapture formula

N = (M × C) ÷ R, where M is the number marked, C is the number caught in the second sample, and R is the number recaptured.

Mark-recapture assumption

The proportion of marked individuals in the second sample equals the proportion marked in the whole population.

Three things that limit population distributions

Environmental (abiotic) conditions, biological interactions and dispersal.

Fundamental niche

The range of abiotic conditions under which a species could persist.

Realized niche

The range of abiotic and biotic conditions under which a species actually does persist.

Why the realized niche is smaller than the fundamental niche

Biotic interactions like competition and predation keep species out of some places they could tolerate abiotically.

How to test fundamental vs. realized niche

Transplant the species into areas outside its range under controlled conditions. If it does fine, biotic interactions or dispersal keep it out; if it fails, abiotic limits do.

Angert & Schemske 2005

Transplanted scarlet (low elevation) and Lewis' (high elevation) monkeyflowers across elevations. Each grew and survived best within its own range.

Hutchinson's niche

The range of biotic and abiotic conditions a species can tolerate, pictured as an n-dimensional hypervolume, with one axis per condition.

Niche partitioning

Species coexist by occupying different regions of niche space.

Dispersal limitation

A species is absent from suitable habitat because barriers prevent it from getting there (e.g., emerald ash borer before humans moved it).

Ecological niche modeling

Using the conditions where a species is found to predict where suitable habitat exists elsewhere.

Ecological envelope

The range of ecological conditions predicted to be suitable for a species.

Chinese bushclover example

Data from its native range in Asia were used to predict where it could spread as an invasive in North America.

Habitat corridor

A strip of favorable habitat connecting two large patches that makes dispersal easier.

Corridor experiment results

Connected patches had more fruit per flower, more butterflies recaptured and more seeds than unconnected ("winged" or rectangular) patches.

Why the experiment used winged patches

They had the same amount of edge as connected patches but no connection, which controls for edge effects.

Ideal Free Distribution

Individuals distribute among habitats so that each gets the same per capita benefit.

Milinski 1979 stickleback experiment

Food was added at 30 vs. 6 Daphnia per minute (5:1), and the fish split about 5:1 (4.8 vs. 1.2), as IFD predicts.

Source-sink populations

Source habitats produce surplus individuals; sink populations would decline without immigrants from sources.