Bio_II Exam 4

Ecosystem Resilience

Ability of an ecosystem to resist change and remain “unchanged” in face of perturbations and/or ability to recover following a change

Disturbance

Force external to community that’s relatively discrete in time that changes resources of physical environment (i.e. fire)

Succession

How communities recover after disturbance

Community Succession

Repeatable change in community composition through time following a disturbance

Community Succession: Primary Succesion

Newly exposed or newly formed land is colonized by living things

Succession that begins new communities + uninfluenced by prior communities

• often starts from bedrock

• not influenced by prior community

• severe disturbance (rare) i.e. lava flow or severe landslide

Community Succession: Secondary Succession

Part of an ecosystem is disturbed and remnants of previous community remain

Succession follows disturbance of pre-existing community + influenced by pre-existing community

• often soil remains that may contain seeds from pre-existing species

• less severe disturbance (more common) i.e. fire, flood, severe winds

Pioneer species

The first species that colonize an area after disturbance

Traits of species that colonize quickly

• Far dispersal distances to travel in from nearby areas unaffected by disturbance

• Hardy, tolerant dormant stages (i.e. fire-resistant seeds)

• Hardy, tolerant adult stages (i.e. some trees can survive being burnt in fires)

• Quick growth in high-light environments

Traits of species that colonize late in succession

• Low dispersal

• Slow growth

• Tolerant of low-light conditions

Climax community

When a steady state (equilibrium) is reached

• persists relatively stably until a disturbance occurs

What are the 3 models of succession?

1. Facilitation

2. Inhibition

3. Tolerance

Facilitation

New bedrock (no soil) can only be inhabited by few, tolerant species- → they make bedrock more habitable for other species (break up rock in soil, add nutrients)

• as environment = more habitable, new less stress-tolerant species that are better competitors move in

• Tends to occur during primary succession

Facilitation model of succession

Assumes that only early-successional species can colonize a recently-disturbed site + these early colonizers alter the site in ways that enable later-successional species to establish

• applies mainly to primary succession

Inhibition

Occurs when a species inhibits colonization by others

• i.e. by monopolizing resources (taking up space, growing leaves tall to block sunlight from seedlings)

• when an individual dies → resources it was monopolizing are freed up

• often trends from short-lived species to long-lived species

Inhibition model of succession

Assumes that any species can colonize a recently disturbed site + they prevent others from establishing —→ over time, short-lived (fast growing) species are replaced by long-lived (slow growing) species

• applies mainly secondary succession

Tolerance

Occurs when early-succession species neither inhibit nor facilitate later-succession species

• species abundances change over time when some species out-compete others

• often, random chance of which species arrives first determines what the dominant species will be

• Late-succession species often just arrived later or grew more slowly than early-succession species

Tolerance model of succession

Assumes any species can colonize a recently-disturbed site and they have no influence on other’s ability to establish —→ over time, species that are weak competitors for resources are replaced by species that are stronger competitors

• applies mainly to secondary succession

Inhibition: Succession Mechanisms

• First colonizer: Any species arriving can establish

• Late-succession species that arrive are: Negatively impacts

Facilitation: Succession Mechanisms

• First colonizer:

• Late-succession species that arrive are:

Tolerance: Succession Mechanisms

• First colonizer:

• Late-succession species that arrive are:

Frequent disturbance would lead to a community dominated by …

Pioneer and early-succession species

Rare or lack of disturbance would lead to a community dominated by …

Late-succession species

• climax community

Intermediate disturbance hypothesis

Biodiversity is highest when disturbances occur at an intermediate frequency

Food Webs

Energy diagrams that depict movement of energy and nutrients

Trophic Levels

Describe the steps of energy transfer along the food web

Primary producers

• Typically form the base

• Autotrophic organisms (can make their own food)

Heterotrophs or consumers

Organisms that can make their own food so must eat other organisms for energy

• Secondary consumer: eats primary consumers

• Tertiary consumer: eats secondary consumers

Apex predator

The top level of a food web

Photoautotrophs

Get their energy through photosynthesis

• i.e. plants, algae, some bacteria like cyanobacteria, phytoplankton

Chemoautotrophs

Get their energy through chemosynthesis

• i.e. some bacteria, archaea, deep sea vent organisms

Decomposers

Feed on the remains of other animals: digesting dead matter → put nutrients back into soil for producers

• are a category of organisms

  • detritivores, fungi, microorganisms (bacteria + protists)

Detritivores

Heterotrophic animals that feed on dead, particulate, organic material (chiefly plant matter)

• i.e. crabs, snails, earthworms, dung beetles, flies

• are detritus feeders (Detritus: particulate, decaying matter like leaves, bark, roots, stems, animal feces, dead animals)

Net primary productivity

The amount of energy captured by photosynthesis in plants minus energy lost through respiration

How much energy is available for primary consumers to eat

• is a lot less than total amount of energy taken in by producers (GPP)

• NPP = GPP - R

  • NPP = net primary productivity, GPP = gross primary productivity, R = respiration

Energy Loss (Trophic Efficiency)

• Each step up in trophic level decreases energy by ~90%

• Total energy (+ usually biomass) decreases at each trophic level

  • Biomass = total mass of organisms in a given area

Where does energy go?

a) Feces: digestion/metabolic inefficiency

b) Growth: producing new macromolecules

c) Cellular respiration: Maintaining homeostasis

Trophic level transfer efficiency …

Varies across ecosystems, typically ~10%

• Formula = (production at present trophic level / production at previous trophic level) x 100

Trophic inefficiency explains why there’s more biomass + biodiversity @ low latitudes:

More energy input in ecosystem (sunlight) = more trophic levels can be supported = more biodiversity possible

Bioaccumulation

Environmental toxins become more concentrated @ higher trophic levels

• Krill (primary consumers) contain trace amounts of mercury → consumers eat large amounts of prey due to trophic inefficiency → energy transfer is inefficient but mercury transfer is “efficient”

Changes in the abundance of a species can cause a …

Trophic cascade

Keystone species

Species that have a disproportionate effect on their community structure

Herbivory

Prey is plants

Predation

• Prey is animals

• Is density-dependent: predation increases when pop density is high, vice versa

  • once predator pop crashes, prey are released from predation pressure

The Lotka-Volterra model of predator-prey dynamics makes unrealistic assumptions

1. Prey population size is only influenced by predation

2. Pop size is only influenced by availability of prey species

Parasitism (+ / -)

• Parasite live in or on host

• Harm host but don’t directly kill it (typically rely on host + need it alive)

• Benefits at cost of host

Parasites vs. Parasitoids

a) Parasites: Harm but don’t directly kill host

b) Parasitoids: Directly kill their host

Symbiosis

When species live in direct and intimate contact with each other

• often used to only indicate mutualistic relationships, but technically it refers to closeness of the interactions

• some mutualisms could be non-symbiotic

• some symbiotic relationships are parasitic or commensalistic

Mutualism (+/ +)

• Both partners benefit

• Can be symbiotic, but not necessarily

• Two types;

  • Obligate

  • Facultative

Mutualism: Obligate

Partners can’t survive outside the mutualism

• i.e. acacia trees + acacia ants → their mutualism has driven evolution of specialized traits

Mutualism: Facultative

Partners can survive outside the relationship

Plant-mycorrhizae mutualism

The most important mutualism on earth

• plants provide sugars to fungi (+) → mycorrhizae absorbs nutrients + water from soil and pass them to plant (+)

Commensalism

One partner benefits (+) while the other is unaffected (0)

• i.e. some types of dispersal, like burdocks, or clownfish living among sea anemone

Amensalism

One partner is harmed (-) while the other is unaffected (0)

• i.e. large grazers step on ants, disrupt nets/burrows of ground animals, crush plants

Niche

Environmental conditions and resources that define the requirements for a species to persist

N-dimensional Hypervolume

The multi-dimensional space of resources (i.e. light, nutrients, structure, etc) used/occupied by a species

• dimensions are environmental conditions and resources

• defined by hutchinson 1957

Fundamental niche

The set of conditions allowing the species to survive if there are no other species interfering

Competition occurs when …

Two species attempt to occupy the same niche (use the same resources)

How do organisms compete with each other?

• Interspecific = between species

• Intraspecific = within species

Interference competition (direct)

Individuals actively prevent others from attaining a resource in a given area or territory

• i.e. Allelopathy: one plant releases toxic chemicals that poison the soil for others

Exploitative competition (indirect)

Consumption of limited resources by individuals makes it more difficult for others to attain the resource

• also called scramble competition

Potential outcomes of competition

• Competitive exclusion

• Niche partitioning/differentiation

• Character displacement

Competitive Exclusion Principle

No two species can share the exact same niche

Competitive Exclusion

The weaker competitor may be entirely excluded from that portion of the niche where overlap occurs

Fundamental Niche

The niche a species could potentially occupy in the absence of competition

Realized Niche

The niche a species actually occupies due to competitive exclusion

There’s often a tradeoff between _____ and _____

Tolerance of harsh environments; competitive ability

• results in generalists and specialists

Generalists

Can occupy a broad fundamental niche but typically are poor competitors

Specialists

Occupy more limited fundamental niche, typically are strong competitors for that niche

Competitive Exclusion

If niches overlap completely, one species may be outcompeted to extinction

Potential outcomes of competition

• Competitive exclusion

• Resource partitioning/niche differentiation

• Character displacement

Niche differentiation (aka resource partitioning)

• Species use different parts of the environment due to interspecific competition

• Species use different parts of the environment in order to coexist

  • species alter their use of the niche to avoid competition by dividing resources among them

Spatial Niche Partitioning

Use the same resource but in a slightly different physical area

• i.e. Rooting Depth: plants retrieve similar nutrients from different parts of the soil column

Temporal Niche Partitioning

Use the same resource at different times

Character displacement

When resource partitioning changes the resources species use which leads to evolutionary changes in traits

• i.e. beak shapes adapting to be different to specialize on different seeds