What are the different types of herbivory?
- 1. Grazers: herbivores that specialize on specific herbaceous plants (grasses, forbes, herbs)
- 2. Browsers: herbivores that eat the leaves, bark and twigs of woody plants. (hares are browsers in winter when grasses aren’t available. Both grazers and browsers have a symbiotic relationship with microorganisms capable of digesting cellulose. For example, hares have a bacteria filled compartment called the cecum.)
- 3. Granivores: eat seed (seed predators, as they kill)
- 4. Frugivores: eat fruits
- 5. Insect herbivores specialize on particular plant parts, as well as particular plant species. Xylem sap and phloem sap have very low nutritional value, but aphids etc. consume a lot of it to obtain necessary amount of nutrients.
What is exploitation
- An ecological relationship with a +- outcome
- Includes predation, herbivory, parasitism
What is herbivory?
Relationship in which a heterotrophic organism consumes tissues or internal fluids of plants or algae.
What is predation?
Relationship in which a heterotrophic organism kills and eats other organisms for food.
What is parasitism?
A relationship in which an organism lives on the tissue of its hosts, reducing the fitness of the host but generally not killing it.
Explain the natural history of parasitism. What are the ways in which they move from host to host?
- 1. Though parasites often cause their hosts significant damage, they also depend on their host for survival. Thus, there is strong selective pressure on parasites to not be so virulent that they kill their hosts.
- 2. Parasites move between hosts using:
- a. Passive transmission: an infective life stage of the parasite lurks where it is likely to encounter a new host.
- b. Active transmission: Parasites move around to encounter hosts.
- c. Direct host to host transmission: An intermediate strategy where parasites don’t leave one host until they meet another.
Most parasites that have a single host species have a free-living life stage where they’re not attached to hosts. Some parasites with multiple hosts have multiple life stages adapted to each host. These complex life cycles can involve multiple transmission modes.
- 1. Because the inside of an organism is much more stable and predictable than the outside, endoparasites are able to take advantage of this.
- 2. Because the parasite slowly feeds on developed tissue, once it is established in a host, it generally has a steady, constant food supply.
- 3. Tapeworms, flukes, fungi, and protists are examples.
- 4. Many are classified as pathogens, as they cause disease. They generally cause greater harm to the human body.
- 1. Examples include mistletoe, some vines, mildew, ticks, fleas, leeches, skin fungi.
- 2. Ectoparasites are more easily transmitted and avoid interacting with the host’s immune system, but have harsher exterior environments and are sometimes exposed to predation.
- 3. Although ectoparasites avoid the immune system of their host, hosts have ways of fighting back, such as mutualistic relationships with ectoparasite consumers.
Why has it been harder to develop drugs to combat major parasitic diseases than bacterial diseases?
Because parasites (eukaryotes) are more closely related to humans than bacteria (prokaryote)
What are parasitoids?
Parasites that develop inside their host and eat it from inside out. When the host is completely consumed, the parasitoid transforms into an adult and crawls out to produce more offspring. The parasitoid life cycle is thus an intermediate between predators and other parasites. This life cycle is common among wasps. Parasitoids are often used as pest-control. Secondary parasitoids (hyperparasitoids) may pose dangers for biological control programs. While the invasion of the host is similar to a parasite, they’re functionally equivalent to a predator.
What is parasite load?
The measure of the severity of infection in a host organism. It can include both the number of parasites or how much damage they do to the host.
Explain the ecological effects of parasitism.
Parasitism begins its impact at an individual scale. Because parasites rob their hosts of resources, host survival and / or reproduction can be reduced even when hosts aren’t killed by parasites directly. (Example: In years with reduced resources, the death rates of Great Horned Owls with higher parasite loads increases.) This leads to changes at the population level and so on.
What are the different types of strategies developed by plants against herbivory?
1. Chemical: producing chemicals that are noxious or poisonous for plants. (caffeine, nicotine, many spices)
2. Mechanical: developing structures like thorns on the stems or trichomes on leaves, sticky saps, spines, toughness (lignin in trees, silica in grasses etc.) (against insect herbivory)
3. Nutritional: growing structures that are less nutritious for grazers (have less N and P)
4. Tolerance: adaptations to regrow quickly after being grazed. (Plants that have been subjected to heavy grazing have been shown to recover faster than plants that haven’t, showing that selective pressures from herbivores may lead to the increased ability to tolerate herbivore damage.)
What are the two different types of defenses present in plants against herbivory? Under which conditions are the more likely to occur.
- 1. Constitutive defenses (defenses that are present at all times, a lot of the physical defenses, most useful under constantly high herbivory)
- 2. Inducible defenses (a defense that is produced in response to herbivory or predation)
How can herbivory affect the ecological composition of an ecosystem?
- 1. Can reduce the number of overall plants.
- 2. Can cause differences in plant composition (communities), especially when herbivores feed on the stronger competitor. In fact, herbivory may lead to increased biodiversity when it affects the stronger competitor, limiting its colonization of the ecosystem.
What are predation strategies?
- 1. Stalking: hiding until they get close enough to pounce
- 2. Pursuit: catching mobile prey
- 3. Ambush: hiding and waiting until a prey comes along.
- 4. Random encounter (spiders)
What is the main difference between herbivores and predators?
- 1. Predators generally have broad diets and switch prey at times when resources become scarce.
- 2. Many herbivores, especially insect herbivores, have relatively narrow diets and feed on a limited range of plants.
- 3. Additionally, herbivores specialize on parts of organisms whereas predators don’t.
What are different animal defenses against predation?
- 1. Chemical
- 2. Physical: developing physical barriers to predation (shells) (Example: the zooplankton Daphnia grows with varying amounts of physical protection depending on the amount of predators in the area)
- 3. Aposematism: developing warning colors, sounds etc. to warn the predator
- 4. Crypsis: camouflaged colors, shapes (example: the food composition of an insect larvae determines how it looks later in life)
- 5. Mimicry: looking like, sounding like, mimicking species that the predator tends to avoid (taking advantage of aposematic species, this is called Batesian mimicry)
- 6. Behavioral : changing behaviour to minimize predation. (day-night, activity and growth reduced in the presence of predators, alarm calls, the ecology of fear)
- 7. Size refuges: Organisms are vulnerable to predation when they’re young, but as adults they’re too large. (threshold size) (Spatial refuges, Temporal refuge)
These strategies may be combined.
What are population cycles?
Periodic increases and decreases in the population of a species. Well known for some boreal species ( arctic foxes, lemmings, voles, porcupines, snowshoe hare etc.)
What are the hypotheses for population cycles?
- 1. Disease
- 2. Reduced food supplies with overpopulation
- 3. Predators
- 4. Physiological stress from overcrowding and predators.