Predation and Herbivory Flashcards
Predation and herbivory
- Predation: one animals eats another
- Herbivory: animal eats plant or algae
What controls prey population?
Predators
-ex: Lynx and hares; when hare more abundant, so are lynx until lynx eats all the hares and starts to die off because not enough food…
What controls plant population?
- Herbivores
- they can be used as biocontrol for ex: goats the keep competing vegetation
low between grape vines in vineyards - can alter physical environment
- ex: Beavers convert forest-bordered
streams into ponds and open meadows
Predators shape ecosystems
- How? Extinctions, population declines, Yellowstone national park example with wolves
o Herbivory: deer eat aspen saplings, limit growth of forest
o Predation: wolves eat deer, limit growth of deer, increase growth of forest
-Also change behaviour of deer
Predation
- Prey must avoid being eaten as much as possible or they will go extinct
- Predators must keep up with prey so as to be able to eat
Predator avoidance: Early detection
- Prey can often detect predators first
• Ex: moths can usually detect bats first; have two pairs of ears (A1 and A2); A1 sensitive to low intensity sound, moth is further away than bat’s detection zone; bat detects moths at ~8m, moth detects bat ~100m; moth acts to avoid detection; how to moths know the bats location? Bat approaching: sound becomes louder and whichever side its approaching from will fire faster (A1 or A2) - A2 sensitive to loud sounds; so if A2 activated then bat has probably already located moth and is close; so moth chooses to play dead (deception)
Predator avoidance: Fleeing
- Makes sense especially in open habitats
- Predators are often bigger, run faster
- Bigger animals may be able to run faster but smaller animals can zig-zag, jump, etc.
Predator avoidance: Hide
- Relatively small size helps
- Camouflage or cryptic colouration
• Background matching
Disruptive colouration
• Transparency (common in aquatic systems)
Predator avoidance: Stick Together
- If you can’t hide, then herd; especially in open areas
• Reduces individual chance of predation (dilution effect)
• Increases changes of predator detection
• Also conserves energy - Herd
• Can be multi species
• May serve to protect young
• Position is important: centre is safer
• But may also attract predators - Stick together
• Flood the market
• Seen in insects; r-selection – emphasize high growth rates, typically exploit less crowded niches, produce many offspring and few of them have probability of surviving to adulthood
Predator avoidance: Call in your friends
- Mobbing calls; call in a mob
- Fairly common in birds
- Found in other animals like meerkats
- Why does this not increase individual predation risk by calling attention to prey?
• They do draw attention to the adults; but do it to protect young
Predator avoidance: Fight
- Physically:
• Physical structures – ex: hedgehogs, porcupines, stingers on stinging slut moth, caterpillar, spikes on pufferfish
• Behaviour – ex: California ground squirrel kick sand in face of snake, or hagfish secrete slime; may be to protect nest or young - Chemically: produces secondary metabolites (organic compounds not directly involved in organism’s primary functions) that taste bad, cause illness or are fatal to predators
- which is better? Why? Cause illness because want to stop predator from trying to eat you
- Naïve blue jays feed on monarch butterflies; vomit; avoid monarchs; learning based on visual cues
- Make own toxin
• Fire salamander makes neurotoxic alkaloid in poison glands and excretes if caught - Get toxin from food
• Ex: monarchs eat milkweed, which contains cardiac glycosides
Predator avoidance: Look Tough - Aposematism
- Aposematism warns of toxicity or bad taste (Monarch, granular poison frog)
Limitations of aposematism
- Only works for predators with good colour vision UNLESS there’s also a pattern
- Prey must die for predator to learn
- Easy meals for predators that by-pass the defense (they are immune to it)
When does aposematism work best?
- Toxin is emetic (causes vomiting)
- Predator is long-lived
- Prey occurs at relatively high densities
Evolution of aposematism
- Apparently altruistic trait – which doesn’t seem to fit with our notion of evolution, natural selection, survival of the fittest…
- Once it is common it may be maintained by antiapostatic selection: selection in favour of the common form, against new, rare and or conspicuous forms BUT
- How can it increase population? Green beard affect (thought experiment)
- Selection for altruism to individuals who share a common, recognizable phenotype because this is generally caused by a common genotype
- Selfish gene wants only to propogate itself
- Altruism directed at other individuals who share that gene – requires specific markers for that altruistic behaviour to recognize the gene (a green beard or something else perceptible)
Individual selection for aposematism
• Maybe conspicuous form will not be killed first after all
- Cryptic at distance, aposematic up close
- Combined with deimatic display (threatening/startling behaviour?)
- Avoidance of novel food by predator
- Maybe pattern has other benefits (thermoregulation, mating, territoriality)
- Maybe colouration comes with other warning cues such as smell
Density dependence in aposematism
- Desert locusts; can be alone or in groups – have different pattern in colouration depending if they’re alone or group; can switch between colouration and patterns mediated by plant alkaloid as dietary switch occurs
- Aposematism may be more effective if you look like other unpalatable species (increased density-
Mullerian mimicry) - Common colours: red, orange, yellow and black
- Limits on Mullerian mimicry;
- Visual predators
- Some prey loss (though less due to multi-species participation)
Predator avoidance: Look Tough - Batesian Mimicry
palatable species looks like one that is unpalatable
Limitations of Batesian mimicry
- Works against certain predators only (those with experience of the model)
- Mimic cannot become too common (apostatic selection) or it will produce benefits to the model species
- Choose a very toxic model
- Be dispersed: negative density-dependence
- Time life cycle
- Predators of the model (co-evolved) will eat it
Evolution of Batesian Mimicry
- From cryptic colouration?
- Random changes?
- From Mullerian mimicry?
- Secondary loss of toxicity?
- Letting competitors bear the cost
Predator avoidance: Avoidance/Distracting
- Flash bright colours (ex: rosy underwing moth)
- Regurgitate (ex: northern fulmer chick)
- Autotomy (self-amputation)
- Draw predator away from nest to protect young (ex: killdeer fakes broken wing to draw predators away from nest)
- Play dead (butterflies do this, snakes)
Predator strategies: Larger than prey?
• Micropredators
- Different from parasites because feed on multiple prey
- Ex: vampire bat, mosquito
- Different from true predator because prey is not killed
- Often smaller than prey
• Social Predators
- Animals that will hunt in a pack
• True predators
- Only ones that are necessarily larger than their prey
Predator strategies: Detect Prey First
- Acute senses
• Sight
• Hearing
• Smell
Predator strategies: Hide and ambush
- Hide then strike
- Ambush predators often capable of extremely rapid strike (Ex: crocodiles)
- May involve cryptic colouration (ex: cougar, chameleon, eastern frogfish)
Predator strategies:
Deception
- Some predators lure prey
Ex: anglerfish
Ex: alligator snapping turtle
Predator strategies: Chase
- Fastest animals are predators
Ex: falcons, sailfish, cheetah
Predator strategies: Hunt together
- Social predators can be smaller than prey
- Increase the chance of detecting prey, success
- Individuals are generally related
- Facultative social predators (ex: lions)
• Individually OR socially depending on the size of the prey
Predator strategies: Immobilize Prey
- Venom
• Ex: snakes, scorpion, spiders - Webs
Herbivory - Avoiding Being eaten: Fight/ Structural Defenses
o Idioblasts (“crazy cells”)
- Plant cells with toxins or sharp crystals that tear mouth of herbivore
Ex: Pigment cells often contain tannins
Ex: Sclereids; double walled, difficult to chew (found in pears)
Ex: Stinging cells; contains toxins that break off in herbivore skin – nettles
Ex: Crystalliferous cells; toxic and can tear mouth of herbivore
Ex: silica cells; epidermal layer of grasses and sedges – have different impacts
o Trichomes (lead and stem hairs) may protect against insects
- Snap beans have hairs that impale caterpillars
o Glandular trichomes
- Produce secondary metabolites that often repel insects
- Essential oils: basil, oregano, lavender
- Occur on ~30% of vascular plants
o Thorns: modified branches (honey locusts)
o Prickles: outgrowth of epidermis (rose)
o Spines: modified leaves (cactus)
Chemical Plant Defences - Secondary Metabolites - Terpenoids
• Terpenoids (terpenes): largest class
- Mono and sesquiterpinoids (2 and 3 isoprenes)
- Essential oils, latex
- May be released from glandular trichomes
- Insect repellants and toxins
Ex: Pyrethrins (monoterpinoids) produced by chrysanthemums – insect neurotoxin; pine resin contains alpha- and beta- pinene; juglone produced by black walnuts: allelopathic; responsible for many flavours familiar to us (peppermint, basil…)
- Triterpenoids: 6 isoprenes
- Structurally similar to animal sterols and steroids
- May be toxic to vertebrates as well as insects
Ex: phytoectysones mimic insect molting hormones (in spinach); limonoids (in citrus) – azadirachtin from neem trees, citronella from lemon grass; cardiac glycosides (foxglove) can cause heart attacks in herbivores (eaten by monarchs)
Chemical Plant Defences - Secondary Metabolites - Phenols
- Tannins
- Anti-herbivore
- Toxic to insects, binds to salivary proteins and digestive enzymes, resulting in protein inactivation
- Found in wine
- Furanocoumarins
- Produced by many plants in response to pathogen or herbivore attack
- Integrates into DNA; apoptosis
- Activated by UV light
- Toxic to vertebrates AND invertebrates
- Grapefruit contains small quantities
Ex: giant hogweed burns, can blind - Isoflavones
- Especially produced by legumes (soy)
- Long term effects on grazers, not fully known why likely estrogenic properties (infertility)
- Urushiols
- Skin irritant
- Sap of poison ivy, poison oak, poison sumac
-Not clear that they are defensive because many herbivores eat them
Chemical Plant Defences - Secondary Metabolites - Nitrogen Compounds
• Nitrogen compounds
- Alkaloids: bitter tasting
- In 20% of angiosperms
- Include: caffeine, cocaine, morphine, nicotine, capsaicin…
- Glycosides: glucose
- Cyanogenic glycosides are stored in vacuoles until membranes are broken by herbivores, in which case they release cyanide, which inhibits cellular respiration
- Glucosinolates similar stores and released cause gastroentinitis
Herbivory - Avoiding Being eaten: Aposematism in plants
o Brightly colours thorns, prickles, spikes
Herbivory - Avoiding Being eaten: Mimicry in Plants
o Mostly to attract pollinators
o Occasionally to deter herbivores
Ex passionflowers mimic butterfly eggs to deter butterflies from laying eggs there
How to be an effective herbivore?
- Withstand physical and chemical defenses
How do herbivores deal with structural plant defenses?
Teeth:
- Low-crowned teeth for frugivores and those that eat soft vegetation (brachydont)
- High crowned teeth for grazers that eat tough vegetation (hyposodont)
- Larger tooth for coarser diet
- Ex of other structural adaptations: head size in grasshoppers (larger head when coarser diet)
How do herbivores deal with chemical defenses?
- Tolerate and store
- Detoxify
- Behavioural adaptations
- Microbial symbionts
- Manipulate microhabitat
Tolerate and store
- Tolerate, store and then use as own defense
Ex: monarch accumulate cardiac glycoside from milkweed, storing it in their wing and exoskeleton then use to deter predators because it can be lethal
Detoxify
- produce enzymes like MFOs (multifunctional oxidases, Cytochrome P-450) that detoxify plant secondary metabolites
Ex: Tobacco hornworm produces P-450 after first eating nicotine, then able to detoxify
Behavioural adaptation
- Eat younger part of plants (ex: winter moths feeds on oak in the spring when less tannins)
- Avoid tough areas (ex: window feeding;caterpillars only eat soft part between veins of a maple lead)
- Geophagy: eat large amount of toxin BUT also eat large amounts of stuff that will neutralize the toxin such as clay or other minerals (ex: frugivorous bats, moose, deer, elephants…)
- Cut off supply of chemical (ex: cucumber worms cut vascular bundles of plant before eating so that chemicals can’t make their way to area they’re consuming)
Microbial symbionts
- bark beetles inject blue stain fungi to weaken tree before feeding
Manipulate microhabitat
- Roll leaves around buds to limit amount of light reaching leaf, production of toxins
- Roll leaves to decrease effectiveness of phototoxins
- Burrow in and form a gall (also works as predator avoidance)
Insect - Plant coevolution
1) plant mutation = novel plant chemical
2) plant enters “predation free” zone; zone expands range and speciates
3) Insect mutation = insect can feed on toxic plant
4) insect enters a “competition free” zone = speciates on new host
5) new plant mutation = new chemical etc..
