lecture 13 - defensive strategies Flashcards
biotic vs abiotic threats
biotic:
- between same species or different
- living
- predators etc
abiotic:
- threat of wave action
- changes in temp or salinity
- things not from organisms
predation as a major selective force
- Almost all organisms have predators
- Predators have a dramatic impact on fitness (no gene passing if dead)
- Predators rarely 100% successful
biotic vs abiotic defensive strategies
biotic: coming from same (conspecific) or different species (predation) –> competition for space, resources, predation)
abiotic:
- threats of save action, change in salinity, etc
- NOT from organism
predation as major selective force
- what makes predation a major selective force?
- almost all organisms have predators
- predators have dramatic impact on fitness (if prey dies, no genetic material passed on)
- predators rarely 100% successful –> the traits of the ones that survive will be passed on to future generations
red queen hypothesis
definition: Prey and predators must continuously improve in performance just to survive over the long term
P-P interactions (predator/prey)
predator prey interactions are reciprocal and dynamic
– both organisms influencing selective environment of one another
arms race
why is there asymmetry in strength of selection on predators & prey ?
- predator loses: simply misses dinner
- prey loses: loses life
asymmetry in selective force —> a lot more at stake for prey vs predator
- predator just doesnt get dinner, whereas prey loses life — natural asymmetry
chart w phases of predatory act & selected defenses
- what are the phases of predation and explain them
search & detection
- self-explanatory
pursuit
subjugation (subdue)
- collected and eaten
selected defenses against SEARCH & DETECTION phase of predation
camouflage (crypsis)
mimicry
hiding
activity patterns
- like DVM (of bobtail squid or zoop)
selected defenses against PURSUIT phase of predation
Fast swimming/running
escape behaviours
- like tail flipping in lobsters
selected defenses against SUBJUGATION phase of predation
armour
- like crab or gastropod shells
retaliation
- fighting back
toxicity
autonomy
- dropping a limb to distract
structural add ons
- creation of long spines –> such as zoop, where too big for predator
induced defenses - definition and explanation
when organisms only have a defense mechanism at certain times - NOT always
induced by presence of predators - will stop growth etc to develop the defenses
can be combo of multiple different types (* Structural *Chemical
* Behavioural)
components of gastropod shell
protoconch
- first part of shell developed in larval stage
whorl
- a cavity formed by calcium carbonate – laid down around central matrix
spire
- consists of all of the previously laid down whorls
body whorl
- most recently laid down
–> has aperture and apertural lip (outer lip of shell aperture)
ways of being crushed
Apertural Lip Crush
Spire Crush
- small part in dactyle –> which is closer to condyle = more force to be crushed as the length output of lever arm is shorter (force advantage)
Apertural Lip Peel
- open like a can opener
gastropod shell defenses against crushing predators
- Overall thickening of shell
- Thickened apertural lip
- Apertural teeth
- waves where shell opening - adds thickness where can break - Narrowed aperture
- less likely to get cheliped in and pry open - Reduced spire
- if less pointy up top, less close to condyle (pivot point) - predator less
advantage to crushing - Thickened tubercles & varices
- projections like spikes
study done on tubercles (spines) - Palmer et al
tubercles are spines on gastropod shells
a porcupine fish preys on gastropods and has teeth that crush them
study done on 2 species of porcupine fish and 2 species of gastropods
3 things found looking at Effect of tubercles on crushing attempts:
Palmer et al study
3 things found looking at Effect of tubercles on crushing attempts:
1) tubercles increase effective diameter
- reduce force advantage of jaws
- shell doesnt get as close to condyle (as far in mouth) so less force can be applied
2) tubercles allow the force to be distributed over a greater area (reduces stress on shell)
3) tubercles allow for the crusher to have less access to area, and the spines can damage predator
- this might be most important
further findings of Palmer et al in relation to size of shell
tubercles allowed for the critical size of the shell to be smaller on average
a gastropod species w strong spines could have a smaller size overall, whereas the species with weak spines would require a larger shell to reach critical size
with weaker spines, the gastropod has to put in more energy and resources to growing to a larger size, w strong spines, need less size bc of these
further study on tubercles (modification of shells)
filed off tubercles of shells and others had spines
the critical length of those with spines removed was needed to be larger than those with spines
presence of spines on gastropods in different latitudes
Number of fish families & species that crush molluscs
Tropical vs. Temperate
found high correlation between species that crush and tropical latitudes (68%)
temperate:
proportion of species crushers = 29%
study showing evidence of convergence - gastropod shell defences
Lake Tanganyika - Tanzania
this freshwater system gastropods w really thick shells - normally thin shells in freshwater bc lack of calcium carbonate
when looking at presence of predators –> much higher here bc crab chelipeds are larger therefore have greater force
indepedently evolving to have thicker shells in different locations to protect themselves from shell crushing predators = CONVERGENCE
Defensive value of gastropod operculum?
example of Taylors sculpin
- suction feeder
- preys on gastropods
- has pegs arising from neurocranium which puts holes in gastropods
40% of unpunched gastropod shells survived completely through fish and out of feces
