Study guide for chapter 15
Describe the "nurse plant" phenomenon.
A nurse plant is one with an established canopy beneath which germination and survival are more likely due to increased shade, soil moisture, and nutrients. The relationship between seedlings and their nurse plants is commensal (an interaction in which one species benefits and the other species is unaffected). However, as the seedling grow into established plants, they compete with their former benefactors for resources.
What are Beltian bodies, and how are they involved in insect-plant interactions?
Beltian bodies are modified leaflet tips which secrete nectar for the ants that live on acacia plants ANTS defend Beltian bodies from insects, herbivores, and even mammalian herbivores (deer) that attempt to eat the plant.
Why might positive interactions be more common in stressful environments?
Facultative interactions (mutualism and commensalism) can REDUCE the negative impacts of a stressful environment (being eaten, provide refuge from competition, improve resource availability, and improve dispersal) INCREASE fitness and coevolution Example: nurse plants
What does it mean to say that the "net benefits must outweigh the net costs" for both partners in a mutualism?
If the benefit/cost ratio changes (due to environmental conditions) then the entire mutualism may change from mutualism to commensalism to parasitism.
Describe the natural history of the fig / fig wasp mutualism.
Life cycle: 1. A mature female pollinator wasp enters the immature fruit through a small opening and deposits her eggs in the cavity. 2. As she enters, she deposits pollen into long and short styled flowers that she picked up from the original host fig. 3. Wasp eggs hatch. 4. The males mate with the females but lack wings, so they create a tunnel to the outside of the fig where the females can escape 6. The females collect pollen as they escape and deposit their eggs into another fig (starting the cycle over)
What is meant by a conditional mutualism?
Mutualism that is dependent on environmental conditions
What are mycorrhizae? and what role do they play in communities?
Mycorrhizae is a symbiotic association between various types of fungi and plant roots. It plays important roles in plant nutrition, soil biology, and soil chemistry. The association is generally mutualistic, but in particular circumstances, mycorrhizae may be parasitic in the host plants.
What prevents mutualistic interactions from being broken down by "cheaters"? and understand the relevant example from yuccas and their pollinators.
Penalties, if they are high enough, may reduce or remove any advantage gained by cheating. If the Yucca moth lays too many eggs within a Yucca flower, the plant selectively aborts that flower.
Define mutualism, commensalism and symbiosis.
Symbiosis: interaction between 2 different organisms living in close physical association Mutualism: a mutually beneficial interaction between two or more species Commensalism: species interaction in which individuals of one species benefit while individuals of the other species do not benefit and are not harmed.
What are some ecological consequences of mutualisms that can extend beyond the interacting pair of organisms?
They can affect the interactions among organisms, the composition of ecological communities as well as the properties of the ecosystems that those communities inhabit. For example : if a dominant competitor depends on a mutualist and the mutualist is lost and the dominant species has reduced performance, then other species' performance can increase.
Give an example of a trophic mutualism, a habitat mutualism, and a service mutualism.
Trophic mutualism: a type of ecological mutualism that refers to the transfer of energy and nutrients between 2 species (resource-to-resource mutualism). Ex: Leaf cutter ants and fungus Habitat mutualism: a type of ecological mutualism that refers to organisms receiving a suitable habitat/shelter from their mutualistic partners Example: Pistol shrimp/gobies: Shrimp and goby share burrow and protect each other (gobies can see and shrimp use their antennae to protect against predators). Service mutualism: a type of ecological mutualism that receive vital services (such as dispersal or defense) from their mutualistic partners Example: fig flowers/wasp pollination
***What are fungal endophytes? and what role do they play in communities?
endophytic fungi live symbiotically with the majority of plants by entering their cells (commensalism or mutualistic) indirect defense against herbivores Fungus receives carbohydrate energy resources Plant receives increased water or nutrient uptake and protection
What's the difference between obligate and facultative interactions? and give an example of each.
obligate interactions: REQUIRED for species (coevolution) ex: leaf-cutter ant cultivate, protect, and nourish fungi the fungi provide food (gongylidia) to the ants facultative interactions: not required for species ex: herbivores (like deer) eat leaves and deposits feces far from the parent which increases dispersal and benefits the plant.
