Species Interactions I

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Species Interactions I

• Diversity of interactions
• The concept of coevolution
• Predation

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Diversity of interactions

• Positive
• Mutualisms eg pollination
• Negative
• Competition
• Predation
• Parasitism
• Herbivory

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Diversity of interactions

• Positive
• Mutualisms eg pollination (III)
• Negative
• Competition
• Predation (I)
• Parasitism (II)
• Herbivory (III)

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Coevolution

• reciprocally induced evolutionary change
  between 2 or more species or populations

• A change in one species acts as a new selective
  force on another species, and counteradaptation
  of the second species, in turn, affects selection
  on the first species
• Common theme in these 3 lectures
• From an evolutionary point of view, parasitism,
  grazing and predation differ in the kinds of
  selection pressures they place on species.

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• Life is an evolutionary arms race
• Predator - prey
• Host-parasite
• Plant-herbivore
• Endless evasion and pursuit though the space of
  feasible biochemical and physical defences and
  attacks

Fisher (1930) discussed the idea that any
well-adapted species will experience a
constantly deteriorating environment owing to
the evolutionary changes in progress in
associated organisms
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• Red Queen Hypothesis (Van Valen 1973)
• Now here, you see, it takes all the running you
  can do, to keep in the same place
• Lewis
  Carroll, Through the Looking Glass.

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Diffuse coevolution

• Often what appears to be coevolution may actually
  result from interactions with many species (not
  just the obvious 2) where it is difficult to
  determine the relative importance of various
  selective forces

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Predation

• the consumption of living animals (prey) by
  carnivorous animals (predators)
• Credited as the cause of many evolutionary
  changes eg in behaviour and morphology. Eg.
  Stanley (1973) speculated that predation in early
  marine environments was the main driving force of
  the earliest radiation of eukaryotic life on
  earth.

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Taxonomic representation

• Most invertebrate phyla have predatory
  (carnivorous) members
• Found among the crustaceans, many chelicerates,
  and several families of insects.
• In some taxa virtually all members are
  carnivorous eg spiders, scorpions and centipedes.

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Types of predators

• (based on mobility of predators and time spent
  handling prey)
• 1. Grazers live upon their prey as a substratum
  and feed only on small amounts (eg nudibranchs on
  sponges), endoparasites are an extreme form of
  this category

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• 2. Ambushers sessile or sedentary and must wait
  for prey to come to them
• Includes
• Sit and wait predators eg crab spiders,
  scorpions, praying mantids, antlion larvae.
• Filter feeders eg many crustaceans.
• May spend a lot of energy swimming and
  simultaneously sieving water eg water fleas, or
  else use their extremities to actively stir water
  and so increase the amount of water sieved eg
  barnacles.

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• Searchers actively patrol for prey and spend
  relatively little time ingesting prey
• May locate prey from considerable
  distances, often by smell eg wandering spiders,
  ladybirds, earwigs, predatory bugs, some crabs
• Include Central place foragers spend
  much energy searching for prey, but return to
  central place eg digger wasps, ants. May locate
  prey quite a distance away

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• Pursuers also actively hunt, but spend more time
  subduing prey (eg starfish, whelks)

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Predator diets

• May be generalist or specialist, some components
  of the diet may be obligatory
• Vast majority of predators have fairly broad
  diets but a few are specialised to a particular
  prey

eg Mastophora, a bolas spider, produces a mimic
of the sex pheromone of several genera of moths
therefore catch only male moths of a few species
--gt case of extreme specialisation.
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Physiological adaptations

• Eg. Sit and wait predators Have to cope with
  waiting a long time between meals feast or
  famine. Adaptations include
• Break down the food externally into a nutrient
  broth eliminates bulky waste products that
  would take up valuable body space during a feast.
  
• Within the midgut, huge branching so that large
  meals can be stored.
• Lack sclerotization on the abdomen so that the
  abdomen can be greatly extended during periods of
  food intake.
• Spiders can increase their body weight
• by more than 50 during a single feeding.
• Low metabolic rate mechanism of
• coping with famine.
• Little specialisation

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Body size

• Predator generally larger than prey
• Several adaptations to expand the range of prey
  sizes taken.
• Eg web-building and use of venom in spiders
• Most spiders can take prey
• 1.5x their own size, some
• can take 2-3x. Web spiders
• lacking either poison or
• web-building tend to prey
• on smaller animals

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• Sociality is another way to increase the size of
  prey taken.
• Eg In ants
• Solitary hunters tend to prey on smaller sizes.
• Those that recruit other workers once prey are
  located can take larger prey.

• Some species forage in
• groups (eg army ants),
• seizing nearly all
• arthropods larger than
• a critical size, can even
• attack reptiles and other
• vertebrates.

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Predator Morphology

• Most arthropod predators have in common
  structures resembling a pair of pincers.
• Eg pedipalps and chelicerae of spiders, some
  beetles and ants have pincer-like mandibles,
  hinged claws on the labiae of dragonflies, tibial
  and femoral modifications of mantids, hindlegs of
  hanging flies.
• Other predators dont have pincers but approach
  and feed on slow-moving prey using sucking
  mouthparts eg heteropterans.
• Predatory molluscs use a drilling structure to
  penetrate shells of prey

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Predator Behaviour

• Influenced by hunger (satiation)
• Eg Recently fed whelks
• Nucella lapillus move around
• less than hungry ones.
• Hungry ones also move in
• straighter paths increases
• probability that they will leave
• the area where there isnt enough food.
• Less directional and slower movements of sated
  animals presumably keep them in areas where there
  is food.

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Predator behaviour (cont)

• Many marine predators use cues from the presence
  of their prey to decide where and when to
  settle.
• Strategy has obvious advantages when food is
  distributed patchily in space.
• Eg Some nudibranch species (specialised
  predators) will only settle and metamorphose into
  the adult stage when prey species is present.
• Adalaria proxima only eats the encrusting
  bryozoan Electra pilosa, will only settle when
  this species is present.

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Prey detection

• Many marine predators can detect prey over large
  distances, eg tactile system of cephalopods,
  detection of burrowing prey by sound and a
  variety of chemical stimuli. Predators such as
  whelks can also detect the best areas of a shell
  to drill improves relative gain of food per
  time spent drilling.
• Spiders respond to web vibrations
• Predators may respond to kairomones that emanate
  from their prey eg clerid beetles respond to the
  aggregation/sex pheromones emanating from bark
  beetles in pine trees

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Predator learning

• Eg. Nucella lapillus fed mussels Mytilus edulis
  for 60 days then presented with new prey
  barnacles.
• Behaviour compared to whelks that had previous
  experience with barnacles.
• Naïve whelks selected larger prey and drilled
  holes in the shells to gain access to the flesh.

• Experienced whelks selected intermediate size
  prey and usually prised the prey open using the
  foot and proboscis which is faster than drilling
  (Dunkin and Hughes 1984).
• Immediate advantages of more rapid food
  processing are to reduce the risk of death while
  feeding and to reduce possibility that another
  predator will displace you.

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Methods of avoiding predation

• Behaviour
• Chemistry
• Morphology
• Crypsis
• Aposematism
• Mimicry

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Methods of avoiding predation

• Behaviour
• Chemistry
• Morphology
• Crypsis
• Aposematism
• Mimicry

Evade detection
Pass information
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1. Behaviour

• Examples
• Vertical migration of water fleas and copepods
  to escape from predatory fish during the daylight
  hours at the expense of a lower phytoplankton
  supply.
• Immobility of sit and wait predators not only
  hides them from their prey but also from their
  own predators.

• Feigning death (thanatosis) eg. coccinellids,
  some spiders
• Group living eg water skaters in group increases
  distance at which predators can be detected, also
  dilution effect

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Other behaviours
Boxer crab
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2. Chemistry

• Examples
• Many species from a wide range of phyla produce
  defensive secretions eg mantle glands in
  nudibranchs, formic acid in ants
• Monarch butterflies Danaus plexippus acquire
  cardenolides from their milkweed food plants
  (Asclepias spp) as larvae and store them as
  highly effective deterrents that cause emesis,
  and subsequent conditioned rejection by bird
  predators
• Alarm pheromones in ants warn nestmates.
  System is quite elaborate and can convey
  information about type of predator and therefore
  about the best defensive strategy to use.

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Chemistry (cont)

• Sequestration
• Aeolid nudibranch digestive system extends into
  the cerata on its back
• Eats the stinging nematocysts without discharging
  them
• Transfers them to its own back to use for
  protection

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Chemistry (cont)

• Bombardier beetle
• Sprays noxious liquid at 100oC in defense against
  ants and other predators
• Spray contains p-benzoquinones - well-known
  irritants
• Precursors of spray stored separately in abdomen
  - explode when combined

Stenaptinus insignis
Arrows show deflectors that aim spray
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3. Morphology

• Predation thought to be a major selective force
  in the evolution of body forms in prey.
• Eg. armature and sculpture of the shells of
  gastropods probably evolved as a response to
  predation by crabs and fish.
• In oceans where crushing crabs are prevalent,
  gastropods tend to have more thickened shells.
  Where peeling crabs are numerous, shells tend
  to have thickened lips.
• Where fish are common, shells tend to have large
  outgrowths on their shells increases the
  effective diameter of the shells.
• Experimental removal of spines from shells
  increases rate of fish predation.

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Morphology (cont)
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4. Crypsis

• Camouflage colouration
• Disruptive colouration
• Strategy for palatable,
• edible animals

Neastacilla sp. on colonial bryozoan
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Crypsis (cont)
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Crypsis (cont)
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• Use of search images by predators - can
  counter crypsis ie after encountering a few prey
  items of a particular morph the predator learns
  to attend selectively.
• Enhanced detection accuracy for a single, or
  small set of similar prey comes at the expense of
  detection accuracy for other prey types.

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5. Aposematism

• warning colouration
• Some colour combinations (eg black red, black
  orange), so consistently advertise noxiousness
  that predators have evolved automatic aversion ie
  dont have to learn from experience

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Question Why arent all prey unpalatable?

• Answer Costs
• Eg. Chemical defences use resources that might
  otherwise be allocated to growth and/or
  reproduction

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6. Mimicry

• One prey species (the mimic) has come to
  resemble the the second (the model) that is
  regarded as unprofitable by predators.

The mimic may itself either be profitable
(Batesian) or unprofitable (Müllerian).
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Mimicry (cont)

• Mimetic individuals reduce their probability of
  being attacked by exploiting the propensity of
  experienced predators to generalise from their
  previously acquired association between an
  unprofitable model and its colour pattern.
• The more dangerous or toxic the model, the more
  likely it is that even a partial resemblance will
  afford mimetic protection.
• Mimicry can involve visual signals or odours

Octopus mimics a flounder. This species also
known to mimic Sea snakes, mantis shrimps, lion
fish and others
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Batesian mimicry

• First described by Henry Bates, 19th century
  naturalist
• Palatable species evolve to resemble brightly
  coloured, unpalatable species

Which is the bee?
From H. W. Bates (1963) The Naturalist on the
River Amazons, Vol 11 p 344)
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Monarch and Viceroy butterflies
Hoverfly and wasp
Caterpillar and snake
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Batesian mimicry (cont)

• African swallowtail, Papilio dardanus a
  polymorphic Batesian mimic
• Unpalatable female forms on right
• Palatable forms on right
• Male on bottom row

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Müllerian mimicry

• First described by Fritz Müller
• Occurs among unpalatable species that have come
  to resemble one another
• Could be regarded as a form of mutualism

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• Many species form Müllerian complexes in which
  each participant is both a model and mimic.
• Within a complex, each moderately unpalatable
  species mimics a highly unpalatable species.

• The unpalatable species may also be models for
  palatable Batesian mimics
• When single pattern of warning colouration is
  adopted by several unpalatable species, avoidance
  learning by predators is made more efficient

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Aggressive mimicry

• Predators can use mimicry to lure prey
• Dangerous predator can mimic a benign species in
  order to avoid alarming prey

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Caveats

• Many traits have several functions so often
  quite difficult to assess the relative importance
  of predation as a selective force.
• Eg melanisms may be involved in crypsis,
  mimicry and thermal regulation.

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Caveats

• Many traits have several functions so often
  quite difficult to assess the relative importance
  of predation as a selective force.
• Eg melanisms may be involved in crypsis,
  mimicry and thermal regulation.
• Some defensive strategies consist of several
  components that act in concert or each against a
  different type of enemy.
• Eg tiger beetles use body size, brightly
  coloured abdomens exposed in flight and defence
  chemicals against robber flies.

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Caveats

• Many traits have several functions so often
  quite difficult to assess the relative importance
  of predation as a selective force.
• Eg melanisms may be involved in crypsis,
  mimicry and thermal regulation.
• Some defensive strategies consist of several
  components that act in concert or each against a
  different type of enemy.
• Eg tiger beetles use body size, brightly
  coloured abdomens exposed in flight and defence
  chemicals against robber flies.
• Some traits reduce the probability of attack
  from one type of predator but increase it from
  another
• Eg Flight helps reduce attack by lizards
  but increases attack by robber flies which
  usually attack flying prey items. Group living
  may increase probability of a predator detecting
  prey, while at the same time conferring more
  protection on individuals.

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Intraspecific predation (cannabilism)

• Can be viewed as a way of killing competitors
  and thereby gaining access to a larger food
  source.
• Widespread amongst predatory arthropods,
  asymmetric in that the larger sizes eat the
  smaller sizes.
• Major mortality factors in copepods, dragonfly
  larvae, backswimmers, some ants, carabid larvae,
  scorpions.

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Ecological effects of predation

• Predatory invertebrates can exert a major impact
  on the structure of both terrestrial and aquatic
  communities.
• Quite commonly predators can drive their prey
  locally extinct and then have to disperse.

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• Example 1 Effects on species diversity
  and community composition
• Experimental removal of Pisaster
  ochraceus, keystone predator reduced diversity of
  community because it allowed a superior
  competitor (Mytilus californianus) to take over.
  Predation of the mussels normally creates space
  for other invertebrates.

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• Example 2 Effect of predation on community
  structure
• Eg The whelk Morula marginalba aggregates in
  cracks in the intertidal rock platform during low
  tide when the weather is warm.
• Prey near shelters consumed very rapidly, but
  prey further away from the cracks not consumed
  because the predator could not find, attack and
  consume them before they had to retreat at low
  tide.
• Leads to haloes of
• free resources around shelters
• that can then be occupied
• by non-prey species.

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Relationship to mutualisms

• Many examples of predators protecting other
  species to get something in return eg. ants and
  acacia thorns, ants and honeydew -secreting
  homoptera, mites and domatia

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Conclusions

• Predation has been an important selective force
  influencing the evolution of many morphological
  and behavioural traits of species
• Predation can also have important ecological
  consequences