Predation, Herbivory, Parasitism

Competition -/-

Competition -/-

Both species do worse in each others’ presence than they do if the other is absent

Amensalism 0/-

• One species is unaffected while the other is harmed

• Beetles positively affected by ibex removal, ibex are unaffected by beetle removal

Exploitation -/+

Predator-prey, parasite-host

Neutral 0/0

• Two species inhabit the same area but do not affect each other

Commensalism 0/+

• Scavenging birds benefit from wolf presence because they feed on carrion

Mutualism +/+

Acacia trees and ants. Thorns provide shelter and food, ants scare away other predators/competitors

Parasitism

• Parasites do not usually kill their host

• Live in or on their host’s body, eating fluids or tissue 

Passive transmission

• An infective life state of the parasite lurks where it is likely to encounter a new host

Active transmission

Move around seeking new hosts

Direct host-to-host transmission

• Intermediate strategy in which parasites do not leave on host until they encounter another

Endoparasites

• Living and feeding inside their hosts 

• Slowly feeding on developed tissue, steady food supply

• Classified as pathogens because they cause diseases

• Tapeworms, flukes, fungi

• Immune system of the host will try to attack the parasite, must have a mechanism to cope with the host’s defenses

  • Skin coating around larva

Ectoparasites

• Live on the outside surface of their host

• Vines, ticks, fleas, leeches

• Eat skin, blood, body fluids

• More easily transmitted among hosts

• Avoid having to defend themselves against immune systems

• They are exposed to predation and harsh exterior environments

• Cleaner wrasse

  • Eats parasites off of fish

• Yellow billed oxpeckers

  • Eats parasites off of buffalo, giraffe

• Hosts have mutualistic relationships with ectoparasite consumers

The human body as a habitat

• The most serious parasite-caused illnesses are from endoparasites

  • They are difficult to attack with drugs

  • Parasites are more closely related to humans than bacteria

Parasitoids

• Kill their hosts

• Develop inside their host and eat them from the inside out

• Once the host is fully consumed, the parasitoid transformers into an adult

• Intermediate between predators

• Common among wasps

• Commonly used to control crop pests

  • Pea aphids on alfalfa and soybean crops with a parasitoid wasp

Hyperparasitoid

• Secondary parasitoid

• Parasite of a parasite

• Lay eggs inside the the larva inside the host

Herbivory

• Grazers

  • Specialize on herbaceous plants

• Browsers

  • Eat the leaves, bark, and twigs of woody plants

• Granivores

  • Specialize on seeds

  • Seed predators

• Frugivores

  • Specialize on fruits

Mammalian grazers/browser have mutualistic associations with symbiotic organisms that are capable of cellulose digestion

• Bacteria in the cecum in snowshoe hares

• Fecal reingestion

Plant defenses against herbivory (4)

• Chemical

  • Producing chemicals that are noxious or poisonous to herbivores

• Mechanical

  • Developing structures like thorns that make is harder for animals to eat them

• Nutritional

  • Growing structures that are less nutritious

• Tolerance

  • Adaptations to regrow quickly after being grazed

Impact of herbivory on plant communities

• Reduce the overall number of plants and can also have a profound impact on the composition of a plant community

• Bog birch

  • Over-browsing by hares

• Likely to affect communities when they feed on a plant that is a strong competitor

  • Goldenrod leaf-miner, allows for higher diversity since they are eating a strong competitor

• When plants have evolved without selective pressure, they are not well-defended

Predation methods (4)

• Stalking

  • Remaining undetected until they are close enough to pounce

• Pursuit

  • Chasing prey, speed and stamina

• Ambush

  • Lies in wait to ambush

• Random encounter

  • Spiders randomly capturing insects in webs

Animal defenses against predation (6)

• Chemical

  • Producing noxious or poisonous chemicals

• Physical

  • Developing physical barriers to predation

    • Shells

• Aposematism

  • Warning colors or sounds to alarater predators that they are not tasty

    • Monarch butterfly, tree frogs

• Crypsis

  • Camouflage to hide from predators

• Mimicry

  • Looking, sounding, other forms of mimicry to seem like a species a predator would want to avoid

• Behavioral

  • Behaving in ways that minimizes risk form predation

Predator-Prey Population Cycling

• Adjusting predation and prey growth rates cannot eliminate cycling and cannot cause prey to go extinct

• Growth of the predator population lags behind growth of the prey population because the abundance of prey stimulates predator population growth

• Deterministic

  • The values of the parameters and the initial population sizes determine exactly what will happen

• Stochastic

  • Includes randomness

Interactions among trophic levels

• Prey can also be strongly affected by the availability and quality of their food

• Krebs

  • Haresin the canadian forest seem to be limited by a combination of lynx predation and scarce food

  • Combined effect of excluding predation and increasing food was successful

  • Ecology of fear

As predation reduce the size of a prey population, the predator population shrinks because there is less food, which allows the prey population to recover

• Predators don’t drive prey to extinction

• An efficient predator can bring populations close to extinction

Assumptions for LV

• There are no effects of crowding

• Both populations are equally likely to meet each other

• The prey species is the only food

• The predator is the only significant cause of death for the prey

• Predators can eat prey instantaneously

• There is no immigration or emigration

Prey density dependence

• Growth rate could depend on density

  • Food limitation

  • Intraspecific competition

• At higher prey densities, fewer predators are required to restrict further prey population growth

• If the prey population reaches K, it cannot grow even if there are no predators at all

• If prey are density dependent and the prey population has increased beyond K, the predator population will grow and the prey population will shrink

• Density dependence is higher when K is lower, population stabilize faster

More realistic predator population

• Predator populations time do the self-limiting due to territoriality, home range size requirements, and interference competition

• With stronger predator self-limitation, predator populations will be smaller and prey populations will be larger at the stable equilibrium point

Adding heterogeneity: prey refuges

• Density-depend limitations can increase stability in predator and prey populations and are another likely explanation how prey populations can survive predation

  • Predator-prey relationship is no the only factor regulation population sizes

• Size of the populations are eq will still be affected by the rates of growth, predation, conversion, and mortality

• What would prevent a predator from being efficient

  • Prey defenses, space, mixing

• With efficient predator and refuges for prey, the system tend more quickly toward the stable eq population sizes 

• With a less efficient predator and refuges for prey, the system oscillates more, and tend more slowly toward the stable equilibrium population sizes

Refuges

• Burrows, tree holes, dense vegetation

• Lower the predator efficiency, increasing the chance that prey population will not be driven to extinction

• Hiding in the dark, safety in numbers, mast-seeding

Metapopulations

• A collections of spatially distinct subpopulations of the same species that are connected via dispersal

• Patchiness in populations can promote stability in predator prey systems and help avoid extinctions

Functional response

Which describes how an individual predator’s feeding rate depends on prey density

Type 1 functional response

• Shows a linear increase with prey density until it hits a maximum threshold, where it levels off

• Not common, only if handling time was so minimal that it could eat as soon as prey was found

• spiders

Handling time

• Amount of time that it takes a predator to kill as consume one item of prey

• Does not include the time spent finding the prey

Type II

• The predator’s rate of prey consumption increases with increasing prey density, but not in direct proportion to it

• Increase as a curve

• As prey densities get higher, the rate of increase in consumption rate gets smaller, gradually levels off

Type III

• Levels off at high prey densities

• At lower prey densities there is a slower initial increase in the predation rate with increasing prey density. Predators have to learn how to catch these prey, ignore them until a certain density

• S shaped curve

• Seals wait to pursue until the salmon density is high enough

Search image

• Improve their ability to detect prey by focusing on certain cues associated with that prey

• Will only be advantageous if they prey is abundant enough

Prey switching

• Frequency dependent predation, occurs when predators show a preference for the most abundant type of prey

• specialists do not do it

Generalists

• Engage in prey switching

• Associated with type III

Coevolution

Occurs when two species that live in close association both adapt in response to selective pressure from the other

• Diffuse

  • With a number of species coevolving in response to each other

• Specific

  • Two species coevolving

• Selection favors high genetic variation

• Continuous shifts in allele frequencies and can maintain high diversity in both host and parasite genotypes

Reciprocal selection

• When two species both exert pressure on the other through natural selection

  • Garter snake TTX resistance and newt TTX strength

• Involves tradeoffs

Red queen hypothesis

• Species that evolve fast enough to keep up with/outpace evolution in their enemies will generally persist longer than those that evolve more slowly

• A species and its enemies continually evolve to keep in the same place

Recombination

• Occurs through sexual reproduction and the process of crossing over during meiosis

• Leads to offspring with different combination of genes than either of the parents and is important for maintaining genetic diversity in population

Sexual reproduction is costly

• Finding a mate, men are useless, recombination, 

• Sex speeds up the rate of evolution, improving the ability to survive in a red-queen world

• Offspring have a higher change of possessing a novel combination of alleles that facilitates success in changing environment