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Today we focus on trophic webs generated by secondary production.

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Original idea that dense life around vents relied on marine snow (i.e. photosynthesis)

Eventually learned hydrogen sulfide was the key– typically highly toxic to most

known organisms. Primary production via chemosynthesis (not photosynthesis)

Chemosynthetic bacteria form thick mats attracting grazers such as amphipods and

copepods.

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Food web base: Sulpher fixing bacteria. Tubeworms have red plumes which contain

hemoglobin. Hemoglobin combines hydrogen sulfide and transfers it to the bacteria

living inside the worm. In return the bacteria nourish the worm with carbon

compounds.

Other web members: shrimp, tubeworms, clams, fish, crabs, octopi.

All are adapted to extreme environment -- complete darkness; 2°C ambient water to400°C (vent openings); pressures hundreds of times that at sea level; and high

concentrations of sulfides and other noxious chemicals.

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Before we get to Predation, we first must characterize those “plant predators” -

herbivores

Defined: Derives energy from plant material

Grazers consume greens, typically on / near ground

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Consumes woody plants (greens and woody material / bark). Typically off the ground.

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Messor barbarus, a grain eating ant is common on the Mediterranean coastline.

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Derive energy from the capture, killing and consumption of living heterotrophs.

Tiger sharks attacking a humpback whale

Carnivores are categorized by hunting method where as herbivores are segregated by

preferred forage type

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What kinds of adaptions would you expect to see in herbivores vs in carnivores?

Herbivores: adaptations to overcome plant defences – digestive enzymes, specialized

teeth, double stomachs of ruminants

Carnivores: adaptations to overcome animal defences – detection, capture and

consumption.

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Patterns of sensory input (sight, smell, hearing, echolocation, pressure gradients,

electromagnetic fields…..) that are associated with prey are learned by predators –SEARCH IMAGE

Salmon eating resident killer whales (loud, physically obvious) vs marine mammal hunting

transient killer whales (silent, cryptic to avoid detection)

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A successful predator is often an invisible one…. Snow Leopard

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Argali rams – cryptic coloration but other defenses too…increase detection by relying

on heard…

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Especially common in visual predators

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Much is made of owl eyesight - but in fact it is highly adapted for sound. An owl will

recognize a certain sound patterns from the forest floor

as a foraging mouse

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Canadian long Eared Owl

Feather and head construction of the owl act as parabolic dishes, collecting andfocusing sound to the ears, easily distinguishing prey noises from other ambient noise.

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When per capita consumption can be increased

Likewise group cooperation is preferred by prey (schooling etc) when per capita

mortality risk decreases

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Experiment demonstrating that the per capita success in bird flocks increases with

flock size – i.e. cooperation does pay in some cases.

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Having more musk ox would provide better protection against wolves. Why aren’t

musk ox herds really large …..like bison?

Because unlike bison musk ox live in very low productivity habitat. A larger herd

would experience starvation and therefore undermine the benefits of additionalprotection from predators.

How is the fine balance achieved? --- Trial and error … which is the basis of

adaptation / evolution

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Which is the cause and which is the effect; wolf pack size or musk ox herd size?

Larger musk ox groups afford greater protection to the group. However, larger groups

require greater amounts of food – but they live in a very low productivity habitat. So

there is a tradeoff.

Reducing predation risk always has energetic trade-offs – no matter what species theprey is…examples? Large group size, armor, repellent chemicals, behaviors …

What explains difference in winter and summer data group size? Opportunity of other

prey means wolves not as persistent (desperate) and therefore smaller herd size

necessary for same level of defence.

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Eyes are a primary search image – therefore prey use this in their own defence

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Red Queen: "It takes all the running you can do, to keep in the same place.” Lewis

Carroll

In more ecological general terms:

In any adaptive system that encompasses competitive interactions (i.e. anythinginvolving “life”), continuing adaptation is needed just in order to persist. Thus,

persistence by definition incorporates the capacity to adapt (change) over time.

Red Queen hypothesis underlies the dynamic evolution of the predation / competition

processes.

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Abalone stopped being cryptic when sea otters disappeared. Now otters are returning

and abalone are again adopting cryptic (burying) behaviour. What mechanism would

explain how this is accomplished?

Those (few) abalones that maintained the“bury

” behaviour would, upon reappearance

of the otter, experience significantly lower predation pressure and therefore increase

their numbers disproportionately in subsequent generations. Over generations the

increased success of the “bury” behaviour ensures it become the dominant in the

population.

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Various toxins / stinging components are common in terrestrial plants aimed at

discouraging herbivores and other species (nesters etc). This strategy is absent in

marine plants…why might that be so?

Too great an energy sink in an energetically restricted environment?

These in picture are all hydroids (an animal, not plant) native to the IndoPacific. All

are capable of stinging in the same way their close relatives jellyfish and anemones.

Animals (consumers) have access to the required energy density in their food to adopt

this (stinging) strategy that is simply not a option for marine plants but given the

greater access to nutrients on land, is an option for some terrestrial plants.

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When humans are the predator we work to get around natural feed back loops

Collapse of Atlantic cod in 1992. In late 1950s a new suite of technologies led to the

introduction of offshore bottom trawlers (red circle) which began exploiting very deep

waters that had up to that point been a sanctuary for cod, especially large old

individuals. Catch skyrocketed and a strong decline in biomass resulted.

Internationally agreed quotas in the early 1970s slowed decline but then the

declaration by Canada of an Exclusive Fishing Zone in 1977 (green circle). This

national quota systems ultimately failed to stop, never mind reverse the decline.

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In natural populations, as the abundance of prey decreases the predation pressure

decreases too (predators will turn to more plentiful prey and/or will decrease via

starvation or reduced reproduction and recruitment). The decrease in predation

pressure allows the prey population to recover (increase reproduction and

recruitment). And so predator and prey co-vary through time, oscillating up and down.

When humans are the predator, we often increase, not decrease predation pressure inthe face of declining prey abundance. In the case of Atlantic cod, decreasing catches

were offset by increasing fishing pressure in an attempt to maintain a constant

economic return. So, as stock abundance declined, “predation” did not decrease but

instead increased – leading to a complete collapse….a scenario that would be

extremely difficult for any non-human predator to replicate.

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Theses silversides have been reared for five generations in laboratory experiments, are

all the same age. All fish shown here are from the fifth generation of each experimental

population. The fish on the left are from from populations in which only large

individuals were harvested over five generations; the fish in the middle are from

populations from which fish were harvested at random over five generations; and the

fish on the right are from populations from which only small fish were harvested overfive generations.

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Two populations of silversides are exposed to different predation regimes. To say if

predation has had an effect we measure individuals after five generations. The green

data reflect fish sizes from a population where only the largest individuals were

predated upon and the blue population only the smallest. Are the two populations

“scientifically different” wrt size after five generations?

It is not just the differences in the mean size that matters. Here we have three possiblescenarios. In each the difference of the means is the same, but the variation within in

group differs. In which scenario would you have the most confidence in concluding

“yes, there is a difference”? (bottom plot). In which scenario would you be most likely

to conclude “No, there is no difference”? (middle). Note that in all three scenarios, the

mean (average) difference in size remains constant. So, BOTH mean and variation

around that mean are necessary before judgment can be made… We learn to assess

situation like this quantitatively.

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Cod response to human predation: Life is short – get young out early (cost? – fewer

young per female) but fishing pressure remains

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Why? Because we as a species can bring to bear much stronger and more persistent

selection pressure than any other “agent” in a natural system.

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Numerous countermeasures to blunt the success (and therefore effect) of predators. In

the case of snow geese, the closer the hatching date is to the “peak date” the greater

success rate of fledging. Therefore coordinated collective action (refined by thousands

of generations of evolution (aka “trial and error”) ) by many can sometimes increase

benefit for each participating individual.

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Locust swarms occur when populations of locust become dense. The crowding forces

larvae in the ground to touch and this constant touching triggers a change in their usual

solitary behavior.

Constant steady emergence would allow predator density to grow to optimal size toharvest locusts – periodic explosion swamps low density of predators.

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Optimizing the ratio of energy spent in pursuit of food vs. energy gained by

consuming food.

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Honey bee: must determine at what point to move onto a new blossom maximize

harvest - Energy limited. The cost of foraging is high and therefore must ensure energy

intake exceeds energy spent, but time is not the limiting factor.

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Kalahari ground squirrel: Builds up heat load while foraging and must return to

burrow to “dump heat”. The cost of foraging is temporal – the longer it takes, the

riskier it becomes.

Both time and energy maximizers operate on the basis of maximizing energyacquisition / time but different “pressures”.

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Regardless if you are time or energy limited, there are two major considerations:

i) Optimize what you eat (maximize benefit)

ii) Optimize how you move about your environment foraging (minimize cost)

Is optimal foraging hard wired in organism or learned?

(in many cases, especially K-selected species, likely a bit of both, but core foundation

is hard wired)

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Fitness in the ecological sense = a quantitative measure reproductive output.

Foraging efficiency results in more offspring – offspring reflect parents efficiency via

DNA

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Specialist vs generalist…?

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Specialist – high energy expenditure in search but high trophic efficiency

Generalist – Low energy expenditure in search but low trophic efficiency

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Line over the variable = “mean”

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The bottom line is read as:

The new item should be included if the average energy gained minus the handling

costs of item i is greater than the old diet plus the now additional search time cost

The key here is that if the forager passes on the new item i, it incurs a cost of

additional search time.

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Search time equal for all three preys species however handling costs of rabbit and

gopher too great for kestral. Red tailed hawk – but handling time differs greatly….but

so does the payoff. But handling time (costs) increases from small to large prey are not

as great as profit.

For the hawk, arrow thickness depicts preference (all things being equal – like relative

abundance of each prey species).

Thus the strength of feedback linking mouse and kestral is much higher than hawk and

gopher (or hawk and any prey).

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You optimize your purchasing decisions just as any other organism might – but using

slightly different currency

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Use “u-pick” berries as example. You don’t stay in a particular position until every last

berry is picked – you move to the next position when the rate of berries picked drops

below a threshold….if you are to be an “optimal harvester”, what is that threshold?

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Head Smashed In Buffalo Jump

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Cumulative energy gain is constant for any patch, regardless of distance from other

patch. What is “optimal” is the tangent of the line determined by its origin.

Tt1 is short travel time (eg. picking berries on a farm) therefore the maximum benefit is

had by moving to a fresh path early

Tt2 is long travel time (eg. picking wild berries) therefore to profit maximally thehigher cost of travel forces the consumer to remain in patch longer than if travel time

was less.

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i) is a behavioral response

ii) is a demographic response

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