Ecology: Species Interactions, Survivorship Curves & Succession

What are mechanical defenses?

Physical structures or actions that prevent predators or other threats from harming an organism.

Give examples of mechanical defenses.

Thorns, spines, shells, armor, thick bark, and protective hairs.

What are chemical defenses?

Chemicals produced by an organism that deter, poison, repel, or otherwise harm predators or pathogens.

Give examples of chemical defenses.

Toxins, venom, irritating secretions, foul-smelling compounds, and bitter-tasting chemicals.

What is the key difference between mechanical and chemical defenses?

Mechanical defenses rely on physical barriers or structures; chemical defenses rely on substances with defensive effects.

What is a survivorship curve?

A graph showing the proportion or number of individuals in a population that survive to different ages.

What does a Type I survivorship curve look like?

High survivorship through early and middle life, followed by a steep decline in old age.

What organisms commonly show a Type I curve?

Humans and many other large mammals; they often produce relatively few offspring and provide substantial parental care.

What does a Type II survivorship curve look like?

A roughly constant mortality rate across ages, shown as a steady decline in survivorship.

What organisms commonly show a Type II curve?

Some birds, small mammals, and other organisms with a relatively constant chance of dying at any age.

What does a Type III survivorship curve look like?

Very high mortality early in life, but individuals that survive the early stage may live much longer.

What organisms commonly show a Type III curve?

Many fish, oysters, insects, and plants that produce many offspring with little parental care.

How do Type I, II, and III curves differ?

Type I: most survive until old age; Type II: mortality risk is relatively constant; Type III: many die young.

What is a species interaction?

An ecological relationship between organisms of different species that affects one or both species.

What is mutualism (+/+)?

Both species benefit from the interaction.

Give an example of mutualism.

Bees obtain nectar while pollinating flowering plants.

What is commensalism (+/0)?

One species benefits and the other is neither helped nor harmed.

Give an example of commensalism.

A bird nesting in a tree, if the bird benefits and the tree is unaffected.

What is parasitism (+/-)?

A parasite benefits while its host is harmed, usually without being killed immediately.

Give an example of parasitism.

A tick feeding on a mammal.

What is predation (+/-)?

One organism captures, kills, and eats another organism.

How is herbivory commonly represented?

Usually (+/-): the herbivore benefits by eating plant tissue, while the plant is harmed.

What is competition (-/-)?

Two organisms use the same limited resource, reducing the success of both.

What is amensalism (-/0)?

One species is harmed while the other is unaffected.

What do the +, -, and 0 symbols mean in species interactions?

+ means benefit; - means harm; 0 means no measurable effect.

What is ecological succession?

The process by which the species composition and habitat of an area change over time as communities replace one another.

What is a disturbance?

An event that affects an ecosystem and can alter its communities or restart succession.

What is primary succession?

Succession that begins on newly exposed land where soil is absent and organisms must establish from scratch.

What are examples of primary succession?

New rock formed by cooled lava and bare rock exposed when a glacier retreats.

What are pioneer species?

Early colonizers that can establish in newly exposed or harsh environments; lichens are an example in primary succession.

What is the general sequence of primary succession?

Bare rock → lichens → small annual plants and lichens → grasses and perennials → shrubs and trees → a mature/climax community.

How does soil develop during primary succession?

Organisms colonize bare surfaces; their growth and decomposition gradually contribute organic matter and nutrients, allowing soil and larger plants to develop.

Why is primary succession usually slow?

Soil and nutrients must develop on a newly exposed surface before many plants can establish.

What is secondary succession?

Succession after a disturbance in an area where soil and nutrients remain.

What is an example of secondary succession?

After a forest fire, grasses may grow first, followed by shrubs and trees, and eventually a mature forest may return.

What is the general sequence of secondary succession?

Disturbance such as fire → early plants/grasses → grasses and shrubs with young trees → mature forest.

What is the main difference between primary and secondary succession?

Primary succession starts without soil; secondary succession begins after disturbance where soil and nutrients remain.

Why is secondary succession generally faster than primary succession?

Existing soil and nutrients remain, so plants do not have to build soil from scratch.

What is a climax community?

The endpoint of succession in a particular climate and geographic setting, persisting in relative equilibrium until disturbance or changing conditions alter it.

Does a climax community remain completely unchanged forever?

No. Disturbances and shifts in resources, climate, or species composition can change a community over time.

How can early plant communities help later communities establish?

Early colonizers can add nutrients to soil; later shrubs and trees can provide shade and cover.

What are examples of natural disturbances?

Storms, hurricanes, tornadoes, lightning, heat waves, cold snaps, heavy precipitation, drought, earthquakes, volcanic eruptions, landslides, disease outbreaks, and pest infestations.

What are examples of human-induced disturbances?

Deforestation, agriculture, urban development, grazing, pollution, mining, logging, drilling, and introduction of invasive species.

What does disturbance severity mean?

The intensity of a disturbance and how much damage it causes.

What does disturbance frequency mean?

How often a disturbance occurs.

What does disturbance scale mean?

The size of the area affected by a disturbance.

What does disturbance timing mean?

When a disturbance occurs within the seasonal cycle.

What mnemonic does the slideshow use for disturbance factors?

SFST: Severity, Frequency, Scale, Timing.

How can fire influence succession?

Fire can restart secondary succession where soil remains; in some ecosystems, periodic fire also helps maintain prairie or savanna communities.

Why might a previous community fail to return after a disturbance?

Biodiversity loss, invasive species, and climate change can alter which species are present and the conditions for recovery.

What is the difference between an intermediate community and a climax community?

An intermediate community occurs during succession before the later mature community; the climax community is the later endpoint described for a particular setting.

If a glacier retreats and exposes bare rock with no soil, what type of succession begins?

Primary succession.

If a wildfire burns a forest but leaves the soil, what type of succession begins?

Secondary succession.

A population has high survival until old age, then mortality rises sharply. Which curve is this?

Type I survivorship curve.

A population experiences a similar chance of dying at any age. Which curve is this?

Type II survivorship curve.

An organism produces many offspring, most of which die young. Which curve is this?

Type III survivorship curve.

Both species benefit from an interaction. Which interaction is it?

Mutualism.

One species benefits while the other is unaffected. Which interaction is it?

Commensalism.

A tick feeds on a host and harms it. Which interaction is it?

Parasitism.

Two species compete for the same limited food source. What is the interaction and its effect?

Competition; both species are negatively affected.