Mark's lectures Flashcards
ecology
The interactions between organisms and their environment. Predators behaving in ways that would allow them to catch and eat prey, and prey behaving oppositely.
Some interactions are behavioural (purple starfish), some are driven by physiology (differences between them, like tolerance).
Behaviour
Interactions between an animal and its environment that involves decision making, decision making is information gathering and processing to choose an appropriate response to information. They don’t need a brain to make decisions, jellyfish make decisions through a nervous system. External environment = internal state = response.
Sensory channels include…
Information sources: visual, tactile (water currents etc.), chemical, electrical, acoustic.
-The type of info available also depends on location.
-For example, in marine environments the visual information may be less important since there is less.
-Sound can be a very unreliable source of information in a marine setting because there tends to be a lot of background noise
-Chemicals can be helpful in the sea since they diffuse very well through water
-Sea water is also highly conductive, so electrical sources could be important as well.
Visual information: predator cues
-Fiddler crabs (Uca vomeris) construct burrows in mud flats, cross mud flats when tide goes out. They feed in the sand. They run back to their burrows when threatened.
-This is anti-predator behaviour in fiddler crabs
-In family Ocypodidae where all species’ males have one larger claw, it is directly sexually selected traits to attract females, and the claws are even useless to feed
-Found that fiddler crabs respond much quicker if gulls take an indirect attack than just diving straight down
-This is because they have compound eyes made of ommatidia which can detect movement, rather than detail or shape
-The eyes are on stalks so they have 360 vision, but their vision is more acute in round periphery (like a donut, so struggle to see directly above).
Visual information: signals
-meral spread in shore crabs is when it opens the claws in an attacking way. Crabs communicate via their postures.
Cue = an unintentional source of information.
Signal = a behaviour that has evolved to convey information.
Display = the activity used to produce the signal.
Tactile information
-the lateral line in teleost’s and elasmobranch fishes
-the line has neuromasts with cupula which detect changes, when pressure changes the hair bends which triggers and impulse in the lateral nerve of the fish
-it can detect water currents and chemicals, and is also used to detect prey and avoid predators. It can detect water currents and ventilation from other animals.
chemical information: foraging risk and hunger level in gobi
-predator cue = the presence of cod
-you can measure foraging behaviour by watching an animal or by analysing its stomach contents
-when sand gobys sense cod their foraging decreases a lot, when the black goby senses a cod nearby they take no chances and foraging levels fall dramatically
-this is because sand gobis are more cryptic and camouflaged, whereas black gobys can’t hide very well
-this means they are also using visual information to make decisions
chemical information: hermit crabs
-they use tactile information to assess shell quality before occupying the shell
-they also use chemical information, and tend to favour shells that had Carcinus maenas before
-hermit crabs also prefer if the shells are intact, especially when there is a risk or predator, they put even more time into choosing their shell
chemical information: crab copulation
-female crustaceans are only receptive to sperm when exoskeleton is soft
-males guard females (pre-copula guarding), and in pre-moult
-guarding a female is costly, so they only guard them when they are receptive to sperm
-males do this by detecting a female sex pheromone, which shows the female is willing to receive sperm (Uridine diphosphate UPD).
-Antennae = contact chemoreception, antennules = distance chemoreception
Electrical information: electroreception
-There is passive electroreception, like when sharks and rays are sensitive the electric fields
-Muscle and nervous activity generate small electric fields, this is very common in marine animals and some egg laying mammals
-Being able to detect electric currents means they can locate prey, and they can also use it to navigate
-They do this with Ampullae of lorenzini (which are the small dots on a shark nose)
-There is also active electroreception which is when they use a special organ in the tail called an electrocyte to generate weak electric fields and currents
-This can be used to stun prey and gather information (electric rays, stargazers and some freshwater fish)
Acoustic information
-Megalopa is a settlement stage larva in crustaceans
-Mechanoreceptors are how crustaceans hear (through vibrations)
-Crabs are known for increased crawling behaviour in response to reef noise
predator-prey interactions
-vision can detect prey, visual cues may be obscured by a complex habitat.
-selection pressures to not be visible may lead to camouflage or cryptyc species.
-rapid escape responses
Predation types
-ambush (just swim with your mouth opening, changing course in minor ways for close prey)
-cruise
-saltatory predation (keep moving and stopping until prey appear within a range of their deception)
Predation example
Dwarf scorpion fish, and porcelain crab
-Difficult to see the crab in a complex habitat or at night
-Could use a lateral line to detect water movements
-Crabs draw movement in through the base of legs, exhale current through the mouth, and scorpionfish can detect these ‘particle streaks’ through their lateral lines
-Scorpionfish use a saltatory predation pattern, prey aren’t that abundant so they can sit and wait to ambush.
They won movement would interfere with the ability to detect the respiratory patterns of crabs. They can detect prey up to 1m away from them, and they seem to use a looping pattern when they move.
Lateral line ambush predators: spotted, eastern and northern stargazers
-Family uranoscopidae, in shallow water of south Australia
-Eyes are on top of their head, so they rely on lateral lines a lot
-They are well camouflaged in the sediment, and are nocturnal predators
-Once the prey passes overhead, they pounce and trap it from behind, they use the lateral lines to detect the fish and their eyes for the final accuracy.
Avoid detection
Hiding is costly, it reduces activity rates and allows less time for feeding or mating. Use camouflage a lot.
-Counter-shading (grey reef shark) = darker on dorsal than ventral side. When seen from the top the dorsal surface blends in with the dark below, when seen from above it blends in with the light. Also makes shark look flatter from the side.
-Disruptive colouration (spotted drumfish) = black and white colouring doesn’t conceal but breaks up the outline making it harder to recognise.
-Colour change in cephalopods = display it for communication, or to match the background. They can also change the texture to blend in, using chromatophores.
Chromatophores
Have a disc shape containing a pigment, they have muscles surrounding it. To change colour they either extend or contract the disk. This is controlled by nerves or responses or electrically.
Decisions + chemical cues in hermit crabs
-Have membranous abdomen which occupy empty gastropod shells
-Need to change shells as they grow, shells also differ in features, like the colour for example.
-They seem to choose the most obvious shell first, and then if they feel like taking a risk, they swap to the most camouflaged one
-They seem to be aware of their own colour, shell colour, and background colour whilst understanding predator cues chemically.
Decision making + competition in clonal sea anemones:
-Acrorhagi = fighting tentacles that contain high densities of nematocysts, only used for fighting
-There are three labour divisions, scouts, warriors and reproducers
-Large reproductive castes, some are small and are ‘scouts’ and some are ‘warriors’
-Fight in large groups for land and recourses
-Behavioural decisions include when a weaker warrior is injured and they choose to withdraw if injured, depends on damage
-Reproductive decisions involve producing more acrorhagi in response to attacks
-The loser is who decides when the fight is over, and the decision isn’t necessarily based on injuries either, sometimes signals
Shell Rapping
Successful attackers rap more vigorously than attackers that give up
-It sounds like someone tapping out in a fight
-There is a longer pause between each rap as they go on
-Number of raps increase with the success of the outcome (eviction)
-Those that give up, rap less and leave longer gaps in between
-If in hypoxic conditions, attackers rap more slowly and give up more readily. When normoxic the gaps are much shorter but they do increase as they go through the fight (as they get tired).
Attackers + Defenders
Attackers = have information about the resource (defenders shell), but no information about the defenders fighting ability. Attackers decide when to give up if they are tired.
Defenders = have information about the attackers fighting ability, but no information about the shell. Defenders give up once they know the attacker is strong. There is information asymmetry between attackers and defenders.
Reproduce
Locate, attract and choose a mate. Normally males locate and attract, and females choose.
Anisogamy
Different sized gametes, females make large expensive gametes in low numbers.
-Males make cheap gametes in much larger numbers, reproduction is cheap
-Males and females only act to enhance their own fitness, neither do it for the good of the species
-Males maximise fitness by mating with many females (promiscuity and competitiveness)
-Females maximise fitness by choosing high quality makes (choosiness)
-Interests between males and females never coincide
Finding a mate: chemical trails in the clam worm
-External fertilisation
-Pre-copulatory female choice is limited, and release cysteine glutathione disulfide (CSSG) which induces males to spawn
-Males and females release gametes during nuptial dance
-Males’ movements don’t change if CSSG is at a low concentration, if the concentration is high they continue to cross over the area until the loops get wider as they try to find the female, they also disperse the concentration by doing that.
Finding and keeping a mate
-Male shore crabs locate receptive females by detecting UDP, but other males want to mate as well so they undergo pre-copulatory mate guarding
-A sex pheromone (chemical signals) is a chemical secreted by one individual that changes behaviour of another
-UDP release may also be an unintentional side effect of pre-moulting
-A chemical cue is called a kairomone because it benefits the receiver, removing the females choice
-She may still get the best male as higher quality males can hold on better
Spermatophore
For all of the spermatophores males produce, some of them may not be used which increases their cost for reproduction. Females can save sperm for later and not even get around to using it if a better male comes around.
-In the giant squid, spermatophores explode out of the male when it comes into contact with a female, it is very aggressive in order to pierce the females skin (anywhere).
Post-copulatory mate guarding in crustaceans
-It prevents replacement of sperm by another male
-May reduce the predation risk for recently moulted females
-Decision to guard after copulation seems to depend on the sex ratio of the population. If there are less females, they seem to guard more.
Sexually selected signals
Sexually selected signals:
-Visual displays often attract females, sexual signals are usually in males
-Since females are choosy, males must try to attract them
Sand goby
Males have a blue spot, and build nests and provide parental care. They also fan the nest to keep it oxygenated and remove toxins. Males can also compete for nest sites. Females tend to go for the male she thinks will be the best parent, if they show vigilance, or attendance or fanning. This means if they waste time showing aggression and fighting, they won’t be attracted. Parental care may be a sexually selected trait. Once females enter the nest, the male performs an acoustic display (the pitch correlates with the males size). Females tend to prefer larger males, and the sound confirms the females choice, and releases her eggs.
Fiddler Crabs
Males wave claws (the bigger the better), and females prefer a higher rate or waving, but males tend to synchronise their waves, they are almost all perfectly synchronised. Females tend to prefer the asynchronous crabs, mostly because they prefer leaders instead of followers.
Sex-role reversal
Usually reproduction is more expensive for females, in some cases male reproduction can be constrained by high parental care and sperm depletion. Males will be choosy whilst females compete.
-But there will never be a male with expensive gametes or a female with cheap ones.
