Predation & Prey Behaviour Flashcards
Describe the different ways in which predators can have negative impacts on the fitness and population size of their prey, referring to both consumptive and non-consumptive effects
Predators can cause directly mortality in prey pop.s by preying on them, eg. death of roe dear by foxes, prickly pear (consumptive)
Can also indirectly cause mortality by influencing behaviour of prey - tadpoles avoiding the side of the aquarium with predators, they’re travelling less and foraging less. Suppressing growth or reproduction. (non-consumptive)
Describe the role that stress hormones can play in mediating non-consumptive effects of predators on their prey
When predators are present animals are more stressed and have smaller offspring, survival rate can also decrease. Mortality effects of predator presence, mortality effects during metamorphosis but no morphological effects (such as smaller size)
What evidence is there that predators can increase prey mortality without actually consuming prey
Prey will emigrate in the presence of predators and this can have a bigger effect than mortality. Fecundity can decrease because of the danger now associated with courtship. eg. Fraser and Gillam 2002
Explain why the fitness of vertically transmitted symbionts may be influenced by the sex of their host
Describe the ways in which vertically transmitted Wolbachia symbionts can influence the sex ratio of their host population
Wolbachia can live in insect eggs but not in insect sperm. Transmission is only from maternal parent to offspring. Therefore, better to be in a female host than a male host.
- By terminating developing males: Males are killed during embryo development, which increases the rate of female births
- Feminization: By making males develop as females, often fertile…
i. e. influence developmental pathways by turning off male development - Induce parthenogenesis: Ova develop without fertilization. Infected females can reproduce without males (creating populations with few or no males)
- Wolbachia-infected males cannot reproduce with uninfected females (reducing those females’ productivity) If fertilization occurs, maternal and paternal chromosomes do not move in sync within the zygote mitotic failure
How do you calculate the functional gender of a plant given its pollen and seed production and the average seed:pollen ratio for plants in the population?
𝐺_𝑖=𝑑_𝑖/((𝑑_𝑖+𝐸〖∗𝑙〗_𝑖))
i = an individual plant
d = the number of seeds produced
l = the number of pollen grains produced
E = (𝑐𝑜𝑛𝑡𝑟𝑖𝑏𝑢𝑡𝑖𝑜𝑛 𝑡𝑜 𝑓𝑖𝑡𝑛𝑒𝑠𝑠 𝑜𝑓 𝑎 𝑝𝑜𝑙𝑙𝑒𝑛 𝑔𝑟𝑎𝑖𝑛)/(𝑐𝑜𝑛𝑡𝑟𝑖𝑏𝑢𝑡𝑖𝑜𝑛 𝑡𝑜 𝑓𝑖𝑡𝑛𝑒𝑠𝑠 𝑜𝑓 𝑎 𝑠𝑒𝑒𝑑)
= ∑2_1^𝑖▒〖𝑑_𝑖/∑2_1^𝑖▒〖𝑙_𝑖 〗〗 for all plants under consideration
G < 0.5: a plant is “more male” than average
G > 0.5: a plant is “more female”
How do Epichloë endophytes influence the functional gender of their grass hosts?
Could be due to long-lasting maternal effects OR genetic differences between plant lineages with infection and those without
Endophyte infection is often associated with elevated levels of reactive oxygen species (ROS) in plant tissues H2O2, O2-, OH*
ROSs are associated with the production of “female” flowers in plant species that have separate female and male flowers. Speculation: endophyte-mediated production of ROS may result in partial “feminization” of flowers
Argue for or against the claim that Epichloë endophytes are mutualistic symbionts of grasses, referring to empirical evidence and models describing the fitness components of wind-pollinated plants
Conclusion: despite the documented benefits of Epichloë infection to grasses, there is still conflict. Arises from the fact that pollen production doesn’t benefit the fungus. Fungal – and also bacterial – endophytes are nearly ubiquitous in plants and are often maternally inherited (no pollen transmission). They may have a significant influence on the reproductive biology of their host plants.
Distinguish between constitutive and inducible defenses
Defenses that are a “plastic” are said to be inducible
“Switched on” or “ramped up” in the presence of enemies
Defenses that are always present, regardless of the presence or absence of enemies, are said to be constitutive
Give examples of inducible defenses in animals and plants, with reference to how the defence is induced (what environmental signal is required), at what stage in development induction can occur, and how the phenotype of the organism changes as a result of induction.
Body form is altered during development if it is growing in an area where predators are common. eg., animals grow thicker shells, longer spines etc. in the presence of predators; thinner shells, shorter spines, etc when predation pressure is weak
What evidence is there supporting the herbivore defense hypothesis relating to endophytes in plants?
Herbivore defense hypothesis: endophytes benefit their host by providing novel anti-herbivore defenses (secondary metabolites)
Microbes have short generation times relative to plants, can evolve more quickly and are therefore better able to keep up with herbivores in the “arms race”
Describe the advantages and disadvantages of constitutive and inducible defenses, with reference to the costs and benefits of defense and the vulnerability of defenses to predator countermeasures
Inducible defenses save costs, but take time to activate. Sudden, intense herbivory > defense may not be activated in time to be of benefit.
