Ecology Exam 2

Question 1

Macroparasites:

Answer 1

Large species such as arthropods, ticks, and worms.

Question 2

Microparasites:

Answer 2

Microscopic, such as viruses, bacteria, fungi and protists.

Question 3

Parasitoids:

Answer 3

Insects whose larvae feed on a single host and almost always kill it.

Question 4

How many parasites can attack a species?

Do parasites adapt to their host?

Specialization helps explain what?

Answer 4

Most species are attacked by more than one kind of parasite; even parasites have parasites.

Many parasites are closely adapted to particular host species.

Specialization helps explain why there are so many species of parasites.

Question 5

Ectoparasites:

Where do they live?

Plant example

Fungal example

Animal example

Advantages

Disadvantages

Answer 5

Ectoparasites live on the outer body surface of the host.

Plant ectoparasites include dodder and mistletoe.

Fungal parasites include mildews, rusts, and smuts.

Animal ectoparasites that eat plants and live on their outer surfaces can be thought of both as herbivores and parasites.
Aphids, whiteflies, scale insects, beetles, nematodes, athlete’s foot fungus, fleas, mites, lice, ticks. Many also transmit pathogens.

Advantages: disperse easy, safe from host immune system

Disadvantages: exposed to enimies, external enviorment, feeding is hard

Question 6

Endoparasites:

Where do they live?

Example

Advantages

Disadvantages

Answer 6

Endoparasites live inside their hosts.
Most don’t eat host tissue, but rob the host of nutrients.

Tapeworms inside stomach

Some live in host’s tissues or cells:
Yersinia pestis, bacterium that causes the plague
Mycobacterium tuberculosis, bacterium that causes tuberculosis
Coronavirus SARS-CoV2, which causes COVID-19

Advantages: easy feeding, protected from external enviorment, safe from enimes

Disadvantages: vunarbale to host immune system and dispersal is hard so must rely on complex life cycle and ensalve host

Question 7

Animal hosts have many kinds of defense mechanisms:

Answer 7

Protective outer coverings include skin and exoskeletons.

Immune systems, biochemical defenses, defensive symbionts.

Vertebrate immune systems
“Memory cells” recognize microparasites from previous exposures.

Other cells engulf and destroy parasites or mark them with chemicals that target them for later destruction.

Some animals eat specific plants to treat or prevent parasite infections.
Woolly bear caterpillars switch from their usual food plants to poison hemlock when parasitic flies lay eggs on their bodies.
Chimpanzees infected with nematodes eat a plant that contains chemicals that kill or paralyze the nematodes (Huffman 1997).

Question 8

Plants defense systems:

Answer 8

Resistance genes

Nonspecific immune responses such as antimicrobial and antifungal compounds

Chemical signals that “warn” nearby cells of imminent attack

Chemicals that stimulate deposition of lignin, making a barrier to an invader’s spread

Plants have many chemical weapons called secondary compounds.

Question 9

Counter Defenses: Parasites

lamellocytes

Two challenges in the human host:

Answer 9

Parasites are under strong selection pressure to develop counter defenses

Ectoparasites must have mechanisms to penetrate external defenses or toxic compounds produced by plants, challenges similar to those faced by herbivores and predators.

Endoparasites must cope with defenses found inside the host.
Some hosts can encapsulate endoparasites or their eggs to make them harmless.
Some insects have lamellocytes—blood cells that can form multicellular capsules around large objects such as nematodes

Two challenges in the human host:
Merozoites multiply in red blood cells, but these cells don’t divide or grow, and don’t import nutrients
Infection by Plasmodium causes red blood cells to have an abnormal shape, which are destroyed in the spleen

Question 10

Host-parasite coevolution:
arms race

Answer 10

When parasites and hosts each possess specific adaptations, it suggests that the species have undergone coevolution.
Coevolution occurs when populations of two interacting species evolve together, each in response to selection pressure imposed by the other.

Transmission is a crucial step in all pathogen/parasite life cycles. Certain species have evolved complex traits that increase their chances to find and invade new hosts.

Some of the best examples of coevolution come from the “arms race” of host parasite evolution. An arms race may stop because of trade-offs:
A trait that improves host defenses or parasite counter defenses may reduce some other aspect of growth, survival, or reproduction.

Question 11

Parasites Can Change Ecological Communities:

Answer 11

Parasites can change the outcome of species interactions, community composition, and even the physical environment.

Predator–prey interactions
Parasites can affect the physical condition of infected individuals.
Predators may be less able to catch their prey, or prey less able to escape predation.

Parasites can also change the behavior of their host

​​Changes in community structure: A parasite that attacks a dominant competitor can suppress that species, causing other species to increase.

Climate change is affecting distribution of diseases

Question 12

The niche:

Fundamental niche:

Realized niche:

Answer 12

Fundamental niche: The full set of resources, plus other abiotic requirements of a species - the potential use of resources - all the environments can exist in - entire pizza

Realized niche: The restricted set of resources that a species is limited to, due to species interactions - organism interacting with each other - but shares pizza
The realized niche is therefore usually smaller than the fundamental niche.

Question 13

Competition:
1. Interspecific competition:
2. Intraspecific competition:

Answer 13

Competition: Non-trophic interaction(organisms that share trophic level not interacting) between individuals of two or more species in which all species are negatively affected by their shared use of a resource.

1. Interspecific competition: Between members of different species
2. Intraspecific competition: Between individuals of a single species

Question 14

Competition mechanisms
A commonly used binary classification of mechanisms:

1. Exploitative
2. Interference

Allelopathy:

Answer 14

1. Exploitative (mutual depletion of shared resources) - two plants in same soil is depleting a shared resource
2. Interference (direct interactions between competitors)
   Individuals of one species grow on or shade other species, reducing their access to light
   Allelopathy: Plants of one species release toxins that harm other species
   Carnivores fighting over animal prey

Question 15

Allelopathy:

Answer 15

Secrete ‘juglone’ : inhibits the growth of other plants
Black walnut trees are so infamous the term “walnut wilt” has been coined
Tree-of-heaven (Ailanthus altissima), sugar maple (Acer saccharum), hackberry (Celtis spp.), and American elm (Ulmus americana) also produce allelochemicals

Allelopathy: Plants of one species release toxins that harm other species

Question 16

Competition intensity
Competition intensity depends on

Answer 16

1. Resource type
2. Resource availability
3. Density of competing individuals

Belowground competition was most intense in nitrogenlimited plots
Aboveground competition for light increased when light levels were low

Question 17

Density dependence

Answer 17

Increased neighborhood density results in stronger competition
Negative density dependence important force shaping forest diversity

Question 18

Competition is often asymmetrical

Experiment silica

Answer 18

Competition reduces available resources for both individuals/species and abundance of both is reduced to some extent
But effects of competition are often unequal, or asymmetrical; one species is harmed more than the other
Example: When one species drives another to extinction

Experiment: growing them alone and in competition with each other
When each species was grown alone, a stable population size was reached and put down the silica
When grown together, they competed for silica, and one species drove the other to extinction

Question 19

Competitive outcomes
1. Competitive exclusion:

2. Coexistence:

Answer 19

1. Competitive exclusion: dominant species prevents another species from using essential resources; the inferior species may become locally extinct
2. Coexistence: living together at the same time or in the same place despite competing for limiting resources (most common)

Question 20

Competitive exclusion

competitive exclusion principle:

Resource partitioning:

Answer 20

Experiments on these and many other species led to the competitive exclusion principle:
Two species that use a limiting resource in the same way (AKA sharing the same niche) cannot coexist indefinitely

Resource partitioning: Species using a limited resource in different ways are able to coexist (lead to competitive coexistence).

One species absorbs green wavelengths most efficiently, the other absorbs red most efficiently
Each species could survive when grown alone in either wavelength
When grown together, one drove the other to extinction, depending on light wavelength

Question 21

Coexistence

Coexistence can occur because of resource partitioning:

Interspecific competition can cause

Character displacement

Answer 21

Coexistence can occur because of resource partitioning:
a population evolves to make use of a different resource
a different area of the habitat
or feeds during a different time of day

Interspecific competition can cause niche differentiation – competing species use the environment differently in a way that leads to coexistence

Two species with essentially the same niche cannot coexist because one will always out-compete and displace the other

Character displacement
When two species compete for resources, natural selection may favor phenotypes that allow them to partition their limiting resources.
Finches inhabiting the Galápagos archipelago are an iconic model for studies of character displacement
Closely-related species differ in beak size
Each species eats a different type of seed:
On islands with only one of the species, beak sizes are similar.
On islands that have both species beak sizes are small and large

Question 22

Factors affecting competition
The outcome competition between species can be changed by features of the:

Answer 22

The outcome competition between species can be changed by features of the:
1. physical environment
2. disturbance
3. interactions with other species

Question 23

1. Physical environment

Answer 23

Chthamalus is found in upper intertidal zone
Balanus is found in lower intertidal zone (will desiccate higher intertidal zones)
Compare growth rates, survival, and/or reproduction of both species, alone and together
Chthamalus is perfectly capable of surviving in the mid-intertidal zone in the absence of Balanus
Experiment: remove Balanus, compare to control
The realized niche of Chthamalus is a fraction of its fundamental niche due to competition with Balanus

Question 24

2. Disturbance

Answer 24

Disturbances such as fires or storms can kill or damage some individuals, while creating opportunities for others
Some species can persist in an area only if disturbances occur regularly
Example: forest plants that need sunlight are found only where disturbance has opened the tree canopy

Question 25

3. Interactions

Answer 25

Herbivores can reverse the outcome of competition between plant species
Ragwort flea beetles are herbivores that feed on ragwort
In the absence of the flea beetle, ragwort was a superior competitor
When the beetle was introduced but it declined precipitously other species dominate the communities

Question 26

Positive interactions

Mutualism:

Commensalism:

Positive species interactions can allow organisms to
live in places where they would otherwise be unable
to survive

Answer 26

Mutualism: Mutually
beneficial interaction
between individuals of two
species (+/+ relationship).
Both populations benefit (+,+).
* NOT altruism. Partners maximizing their fitness.
Major role in generating biodiversity.
* Colonization of land by plants with mycorrhizae.
* Diversification of insects & flowering plants over past 100 M years.
* Fundamental to biology of corals, lichen, etc.
The currency of mutualisms:
food (nutrition), protection,
transport

Commensalism: Individuals
of one species benefit;
individuals of the other
species do not benefit but are
not harmed (+/0 relationship).
Many species form +/0
relationships with
organisms that provide
habitat or access to
food/resources
* millions of species form +/0
relationships with foundation
species that provide habitat:

Question 27

Symbiosis ≠ Mutualism

Answer 27

Mutualism = an interaction between species that is beneficial to both (+/+).
Symbiosis = two or more organisms existing in close association.
*sym = together [Latin]
*bios = life [Greek]
Albert Frank (1877) = “all the cases where two different species live on or in one another… based on mere coexistence”.
German mycologist Heinrich Anton de Bary (1879) = “the living together of unlike organisms”.
Symbioses can be parasitic (+,-), mutualistic (+,+) or (0,+) (0,-) (0,0).

Question 28

Mutualisms – definitions & distinctions
Obligate
Facultative

Answer 28

Obligate = necessary
association required for the
survival and reproduction of
both species

Facultative = beneficial but not
essential for survival and
reproduction

Question 29

Mycorrhizal associations

Answer 29

Substantial amounts of C are
allocated to mycorrhizal fungi
by plant hosts, In return these fungi acquire
and provide the host with soil
nutrients

• Ectomycorrhizae: The
  fungus grows between root
  cells and forms a mantle
  around the root.
• Arbuscular mycorrhizae:
  The fungus penetrates the
  cell walls of some root cells,
  forming a branched
  network called an
  arbuscule.

Question 30

Lichens

Coral

Ubiquitous

Answer 30

Lichens
* Mutualism between fungi and algae
(some cyanobacteria), many of which can
fix N2
* Obligate for many of the fungal components of lichens.

Coral
Corals form mutualisms with symbiotic algae.
* The coral provides the alga with a home, nutrients (nitrogen and
phosphorus), and access to sunlight.
* The alga provides the coral with carbohydrates produced by
photosynthesis.

Ubiquitous: being present virtually everywhere
Trunks of trees, rocks, buildings
Even in the most extreme environments: high altitudes in Himalayas,
hot deserts of Africa, cold Arctic, barren lava fields.

Question 31

Mutualisms –distinctions
Protective

Answer 31

Protective = mutualist provides shelter, physical
protection, or chemical/immunological defense.
* e.g., bullhorn Acacia & Pseudomyrmex ants

1. Protection mutualism
   * Ants protect plants from herbivores and/or
   protect herbivores from their natural enemies.
   * The price of doing business with ants usually
   comes in the form of concentrated sugar.

Ant – Acacia mutualism
Widespread, occurs on different continents
and with different species.
Ant benefits:
* Food
* N-rich Beltian bodies.
* Extrafloral nectaries.
* Nest site
* Hollow thorns.

Plant benefits from ant mutualists
* Herbivore defense.
* Excreted nitrogen.

Question 32

Mutualisms –distinctions
Nutritional

Answer 32

Nutritional = mutualist improves nutrition or confers
access to a novel limiting resource.
* e.g., mycorrhizae, termite symbionts

2. Nutritional mutualism
   * Provide a limiting nutrient for insects
   on nutritionally poor or unbalanced
   diets.
   * endosymbiont = organism that lives
   inside of the body of another

Question 33

Mutualisms –distinctions
Dispersal or Transmission or Transportation =

Answer 33

Dispersal or Transmission or Transportation =
dispersal of reproductive propagules (e.g., seeds),
transmission of pollen, or transportation of
individuals.
* e.g., figs & fig wasps; bees & many flowering
plants
3. Transport/dispersal mutualism
* Important for sessile species
(seed dispersal).
Coevolution of
pollinators/plants

Question 34

Benefits of Pollination

Answer 34

1.Unlike animals, plants are rooted, and
cannot seek and choose partners.
2. Plants gain higher rates of gene
exchange among compatible partners.
3.Animals gain a source of food and
energy.
4. Each inadvertently assist the other as
they pursue reproductive self-interests.

Question 35

Conflict between flower and pollinator

Answer 35

Conflict between flower and pollinator
* Plant selected for minimizing costs (rewards),
maximizing pollinator fidelity.
* Pollinator foraging behavior is a major determinant of
flower success.
* Pollinator selected for maximizing foraging
efficiency.
* Wants large reward for minimal effort.

Question 36

How does plant manipulate vector behavior?

Answer 36

Plant offers rewards to atract and entrain
pollinators

• Too small a reward, won’t be visited
• Too large a reward, vector will be satisfeyed, won’t visit more flowers
• Too many flowers open at same time, vector
  won’t leave plant

Question 37

Evolution of mutualism

Cheaters

Answer 37

• How does cooperation evolve? Mutualisms as
  “delicately balanced antagonisms?” (Janzen
  1985).
• Problem: conflict of interest over the optimal
  amount of resource to provide your partner
  (reciprocal exploitation = max. individual gain).
• strong temptation to defect à ‘cheaters’ should be
  prevalent.
• cheaters punished for relationship to remain
  evolutionarily stable?

Ex: Yuccas have 1 species of Yucca moth that pollinates each of them.
If that moth goes, so goes the yucca species.
* Female moth
collects pollen in one
yucca and lays eggs
in another,
depositing the
pollen in this flower.
* Cheating can occur if
moths lay too many
eggs and the larvae
eat too many seeds.

Penalties can be imposed to cheaters
Yucca moths are suggested to
have pheromonal means of
detecting floral egg status:
laying fewer eggs in pre-infested
flowers.
* But yuccas can selectively abort
flowers with too many eggs,
before the moth larvae hatch
(selective abortion).
* Manipulation of host physiology
through regulating Indole-3-
acetic acid: reduces the
probability of fruit abortion.

Exploitation & the stability of mutualisms
Cheaters: seek to obtain the reward while not providing any services in return