Lecture 7: Nature of predation Flashcards
define predation
> consumption of one organism (the prey) by another organism (the predator) when the prey is alive when it is first attacked by the predator
what are some taxonomic classifications of predation?
> carnivores consume animals
herbivores consume plants
omnivores consume both ( more correctly prey from more than one trophic level; e.g., plants and herbivores or carnivores and herbivores
what are some functional classifications of predators?
> true predators
grazers
parasites
parasitoids
what are tue predators?
> kill prey more or less immediately after attacking them
kill several or many different prey individuals during their lifetime
often entirely consume prey
lions, bears, venus flytrap
what are grazers?
> attack large numbers of prey in their lifetime
remove only part of each prey individual
effect on prey individual, although typically harmful, rarely lethal in the short term.
wildebeest - grass
larvae on gum trees
mosquito on humans
what are parasites?
> consume ‘part’ of their prey, typically harmful but rarely lethal in the short term
attacks concentrated on one or very few individuals in their life
intimate associations between parasites and their prey (hosts); not seen in true predators and grazers
tapeworms
aphids - stay on one plant for entire lifecycle
what are parasitoids?
> insects (mainly) in the orders Hymenoptera (wasps) and Diptera (flies)
adults are free living but eggs are laid in (or near) other insects (other arthropods, and also spiders)
immature larvae live in/on host, eventually killing and consuming all of it
an adult parasitoid emerges from what is apparently a developing host
biological control
intimate relationship with hosts
what is special about parasitoids?
> they straddle the other categories
intimately associated with host (like parasites)
do not cause immediate death of host (like parasites and grazers)
their eventual lethality is inevitable (like true predators)
“predation” largely determined by the rates at which females lay eggs: each egg represents an attack even though it is the larva that consumes the host/prey
most parasitoids have been intensively studied in “predator-prey” interactions and they’ve provided a wealth of information
describe the prey fitness and abundance of each type of predator
> true predators, grazers and parasites all obtain resources from prey that reduce either individual fecundity or probability of individual survival and thus reduce prey abundance
true predators: immediate/rapid death
grazers and parasites: profound, but more subtle effects
- high levels of herbivores + drought caused all subjects to die
- grazing reduced growth
parasites reduce animal arrival time to Africa, therefore reducing mating rates
does reduced survival/fecundity lead to reduced prey abundance?
needs to be tested via experiments
how do grazers and parasites interact with other factors to reduce fitness and abundance?
> although they don’t kill prey immediately, make them more susceptible to other mortality factors
red grouse with worms were more susceptible to predation then red grouse without worms.
how do plants compensae for herbivory?
> removal of leaves may decrease shading and increase photosynthesis in remaining leaves
plants may compensate using stored reserves
root: shoot balance maintained by transferring production to damaged parts
plants can respond by producing defensive structures or chemicals
prolonged snail grazing induces seaweed to produce phlorotannis -poisonous
how do some individuals compensate and defend against predators?
> chemical defences
- noxious odour: stinkbug
- alarm pheromone: aphids - tells other aphids to disperse
cryptic colouration
- flounder: colour and pattern changes rapidly to match bottom sediments
object resemblance
- stick insects resemble the plants upon which they feed
Warning colouration
- aposematism (advertising of distastefulness)
- predators must experience unpleasant taste/ toxicity of these animals before learning to avoid them
- monarch butterfly, poison dart frog
protective armour
- spines on echidna
behavioural defences
- alarm calls and mobbing in birds
- grouping in mush oxes
what are the two differnt types of mimicry in nature?
> Batesian mimicry:
- edible species resembles inedible species in same habitat
- monarch butterfly and viceroy butterfly
- coral snake and scarlet king snake
müllerian mimicry
- unpalatable or venomous species share similar colour pattern
- predator has only to be exposed to one species before learning to stay away from similarly coloured species
- social wasps, digger wasps, cinnabar moth larvae
both batesian and mullerian mimicry can occur together
what are some techniques organisms employ to satiate predators?
> mast year = a year in which there is synchronous production of a large volume of seed, often across a large geographical area
the predators of the seed cannot consume all of it
higher survival in a mast year
as individual predators become satiated
synchronised emergence of a cicada
prey death is low at the start
as pop decreases, predation increases
what are the effects of predtors on prey?
> is predation always harmful?
for the individual preyed upon, yes by definition
for the population, not always:
- there may be compensatory growth, survival or reproduction in survivors (amelioration of predation effects reduced intraspecific competition)
- individuals killed may not necessarily be a random sample of the population
- natural selection, weak, old, young ones selected by predators
disproportionate amount of fawns killed as they are easier to catch, may not have learnt to avoid predators, may not be able to outmaneuver predators
