Ecology Final Exam

Starts at lecture 10/30 Parasitism/Infectious disease

Parasite

An organism that lives in or on another organism, which consumes host resources or causes harm to the host

Pathogen

A parasite that causes disease

Endo vs Ectoparasites

Endoparasites live inside an organism, ecto lives outside

Intracellular vs intercellular parasites

Intra- live inside of cells of host

Inter- live in spaces between cells of hosts

Example of inter and intracellular parasites

• Intercellular - tapeworms and flatworms

  • Intracellular - Viruses, protozoans (malaria)

1 and 3

Reservoir for SARS-CoV-2

Horseshoe bats

Parasites vs parasitoids

Parasitoids always kill their host, parasites do not always kill the host

Horizontal vs vertical transmission

• Horizontal transmission: Parasite moves between individuals other than parent and offspring

  • Vertical: Parasite is passed down from parent to offspring

Vector

Organism that disperses parasites between hosts, such as a mosquito distributing malaria

What 4 factors influence host infection?

• Mode of entry (through a break in outer barrier, airborne, etc.)

• Host range of parasite (number of hosts, options for pathogen survival)

• Existence of reservoir species

• Evasion of host immune system

1, 2, and 3

Susceptible, Infected, Resistant (SIR) model

The simplest model of infectious disease transmission that incorporates immunity

In the SIR model, g is _______

rate of transmission

In the SIR model, b is _________

rate of recovery

R0 >1

Epidemic/pandemic spread

R0<1

No epidemic

Label these as susceptible, recovered, and infected

Blue - susceptible, red = infected, grey = recovered

Herd immunity threshold

Ph>1-(1/R0), Ph = fraction immunized

Host adaptations to combat parasites

• Immune system

• Mechanical/biochemical defenses

• Medicine

Coevolution

When 2 species evolve in response to each other

Intraspecific competition

Occurs within individuals of the SAME species

Interspecific competition

Occurs between individuals of DIFFERENT species

When would intraspecific competition usually occur?

When resources are limited

Resource

Anything an organism consumes that causes an increase in population growth rate when it becomes more available

Liebig’s law of the minimum

• Population increase is limited by resource that is the least available

Yield grows but growth slows and eventually stops

Competitive exclusion principle

Two species can’t coexist indefinitely if they use and are limited by the same resource

More related species experience _________ competition

Stronger/ more intense

D

Label parts of the equation

r1= growth rate of species 1, N1= population size, K=carrying capacity, alpha= competition coefficient for species 1

What factors can affect coexistence/ the ability to compete well?

• Abiotic conditions, such as tides

• Disturbances - forest fires

• Interactions with other species, such as predation and herbivory

Exploitative competition

When individuals drive down the abundance of a resource so that others have more difficulty surviving and reproducing

Interference competition

When individuals compete directly with each other for resources

Apparent competition

When two species have a negative effect on each other through the presence of an enemy, such as a predator or parasite

Aggressive interactions

A form of interference competition

Allelopathy

When organisms use chemicals to harm competitors, such as when bacteria secrete antimicrobial substances to kill other competitors

Apparent competition example

Pheasant and partridge competition from parasite eggs, ants in devils gardens

I and II

Generalists

Types of mutualists where species interact with many other species

Specialists

Types of mutualists where species interact with only one or a few closely related species

Obligate mutualists

Require each other for persistence

Facultative mutualists

Species where the interaction is not critical to the persistence of either species

Zooxanthellae

Photosynthetic mutualistic algae that live within coral

Mycorrhizal fungi

Fungi that surround plant roots to help them get nutrients, such as water and minerals

Endomycorrhizal fungi

fungi whose hyphae penetrate root cells between cell walls and the cell membrane

Ectomycorrhizal fungi

Hyphae surround the plant roots and enter between cells but not commonly into cells

Arbuscular mycorrhizal fungi

Fungi that are endomycorrhizal and infect many trees and grasses

mutualists

Yucca moths and pollination

Yucca moths lay eggs within the flower, pollinating them in the process but too many eggs per flower leads to reduced productivity

Mutualisms between plants and animals

• Animals eat fruit of plants, help to disperse their seeds

• Some animals are pollinators

Positive to negative interactions

Interactions that were initially mutualism can shift to predation or parasitism if one species no longer receives a benefit

Cheating

When one species in a mutualism receives a benefit but doesn’t provide one

B

Ecotone

Boundary created by sharp differences in environmental conditions over a short distance, also accompanied by major changes in species composition

Interdependent communities

Species abundance is positively linked

Independent communities

Species abundance is not positively linked

Removing a species from an independent community would have what effect on other species?

Either negligible or positive effect on other species

II and III

Species richness

Number of species in a community

Relative abundance

Proportion of individuals in a community represented by each species

Rank abundance curve

Curve that plots relative abundance of each species from most to least abundant

Species evenness

Difference in relative abundances between species in a community

decreasing number of species sampled

Why does species richness decline with increased habitat fertility?

Increased habitat fertility promotes the growth of the most dominant competitors

How does higher habitat diversity affect species diversity?

Increases proportionately

Keystone species

A species whose presence affects the abundance of other species in the community significantly

Ecosystem engineers + example

A keystone species that affects communities by influencing habitat structure, ex. beavers

Food chain vs food web

• Food chain: linear relationship between feeding of organisms

• Food web: links that represent multiple feeding relationships

Trophic level

Feeding level in a food web, ex. producers/consumers

Tertiary consumers

Apex predators

Secondary consumers

Mesopredators

Primary consumers

Herbivores

Guild

Species that feed on similar items within a level

Direct effects (food web)

Interactions between species that do not involve other species

Indirect effects (food webs)

Interactions that involve one or more intermediate species

Trophic cascade

Indirect effects in a community initiated by either a predator (top-down) or producer (bottom-up)

Trait mediated indirect effect + example

An indirect effect caused by changes in traits of an intermediate species, such as behavior

Example = grass + grasshopper + nonlethal spider, spider causes change in behavior of grasshoppers to avoid potential predation

Bottom-up control

When abundance of trophic groups is determined by the energy produced by produces

Top-down control

Abundance of trophic groups is determined by predators at the top of the food web

Community stability vs resistance vs resilience

• Stability: ability of a community to maintain structure

• Resistance: amount a community can resist change after a disturbance

• Resilience: how quickly a community can return to its original state after a disturbance

Alternative stable state

After a disturbance, a community can form a new community structure that is resistant to change

Succession

Change in species composition over time

Seral stage

an immediate stage found in an ecological succession

Pioneer species

Earliest to arrive at a site in an ecological succession

Climax community

Final seral stage in an ecological succession

Chronosequence

Sequence of communities that exist at a given location over time

Ways of observing succession

• Directly observing changes over time

• Examining pollen in sediment and layers/ lakes

Primary succession + example

Development of communities within habitats that are initially devoid of plants and organic soil

Ex. lava flows

Secondary succession

Development of communities in disturbed habitats that have no plants but do have organic soil

Glacier retreat often leads to _________ succession and wildfires lead to __________ succession.

Primary, secondary

Properties of intertidal community successions

• Succession occurs rapidly since dominant species have a short generation time

Stream succession properties

• Streams have rapid succession since organisms can easily move downstream after a disturbance or to areas where a disturbance occurred, ex. invertebrates moving to a flooded area

How does lake succession occur?

• Open lake experiences a drought

• Plants colonize newly exposed sediment

• Drought ends and plants are brought to the lake surface

• Peat fills the lake basin eventually

What does a succession productivity curve look like in terms of species richness?

• Rapid increase in species diversity at first

• Small plateau

• Small decline

Label A and B as either late or early succession (slow or fast)

a= early succession, b= late succession

Facilitation (succession)

Mode of succession in which one species increases the chances of a second species becoming established

Inhibition (succession)

One species decreases the chances of another species becoming established

Tolerance (succession)

Species do not alter the environment in ways that affect other species chances of establishment

Priority effect (succession)

Arrival of species at a site affects the colonization/establishment of other species