Lecture: Chapters 15-16 Predation and Mutualism Flashcards
Importance of predation
- Defines food chains and food webs
- Determines behavior, population dynamics and spatial distributions of both prey and predator
- Driving force of adaptations; appears to be a stronger evolutionary force than other species interactions
Predation
The consumption of one (live) organism by another, in whole or praty
True predators
Organisms killing their prey and often consuming it in whole
Grazers
Organisms consuming their prey (e.g. plants) in part, without killing them (e.g. some herbivores)
Parasites
Organisms obtaining nutrients from (and usually attached or inside) a host, without necessarily killing it(one or few hosts per lifetime)
Parasitoids
insects that lay an egg on or in another insect host. After hatching, larvae remain in the host, which they eat and usually kill
Herbivores
Herbivores eat differnet parts of the plant. nitrogen content of plants is relatively low compared to animals
Functional response
consumption rate of a single predator; number of prey consumed per predaotr per unit time
Numerical response
predator reproduction rate
Lotka-Volterra
Prey growth in the absence of predator : exponential - the functional response of the predator
Type I functional response
The predator can increase its consumption indefinately as the prey population increases. Each predator consumes the same proportion of the prey population. This is unrealistic because of predator satiation (predator becomes full and stops feeding) and because of handling time
Type II functional response
each predator consumes a smaller proportion of the prey population as the prey population size increases. If N is small, Type II model close to type I. This is due to handling time.
total feeding time = searching time + handling time
Type III functional response
At high prey density, type III functional response is similar to type II for the same reasons. but at low prey densit, predator consumption increases at a slower rate and results in a n S shaped sigmoid curve
Trade offs - optimal foraging theory
Foraging - survival, growth, reproduction; Defense ; Predator avoidance ; searching for mates ; carying for young
Natural selection
may favor ‘efficient’ forages
- individuals maximize energy intake or intake of some nutrient per unit of effort
- maximize benefit (fitness) and minimize cost (time, energy spent on foraging)
- what toe at? maximize net energy gain
- many species may be required to satisfy nutrional requirements
Physical defenses
- large size
- rapid movement
- body armor
aposematic coloration
predators learn not to eat organisms that have toxins
crypsis or cryptic coloration
the prey is camouflaged or resembles its background
mimicry
the prey resembles another organism that is toxic or very fierce
mullerian mimicry
co-mimicry among several species of noxious organisms
batesian mimicry
harmless species mimic noxious species
plants: predator satiation
some produce huge numbers of seeds in some years and hardly any in other years
the plants hide (in time) from seed-eating herbivores then overwhelm them by sheer numbers
structural defenses
tough leaves, spines and thorns, saw-like edges, pernicious haris that can pierce the skin
induced defenses
produced in response t herbivore attack. eg some catci increase spine production
chemical defenses
secondary compounds: toxic chemicals to reduce herbivory
platn defneses can be overcome by herbivores
some herbivore have digestive enzymes that allow them to tolerate plant toxins
symbionts
organisms that live in or on others organisms
parasite
consumes the tissues or body fluids of the organisms on which it lives (the host)
pathogens
parasites that cause diseases
parasitoids
insects whose larvae feed on a single host and almost always kill it
macroparasites
large
extracellular
grow but don’t reproduce inside host
arthopods and worms
microparasites
microscopic, such as bacteria
often intracellular
usually reproduce within host
often very numerous
ectoparasites
live on host
plant hosts
animal hosts
endo parasites
live within host
tapeworms, bacteria
hosts have adapatations for defending themselves against parasites, and parasites have adaptations for overcoming host defenses
parasites exert strong selection pressure on their host organisms and vice-versa
Defenses and counterdefenses
Host organisms have many kinds of defense mechanisms
Protective outer coverings include skin and excoskeletons
many parasties that do gain entry are killed by the host’s immune system. Immune response has costs as energy is diverted from feeding, reproduction etc.
vertebrate immune systems
have memory cells that can recognize microparasites from previous exposures
using plants to fight parasites
some animals eat specific plants to treat or prevent parasite infections. Chimapnzees infected with nematodes seek out and eat a bitter plant that contains chemicals that kill or paralyze the nematodes
parasites can reduce the sizes of host populations and alter the outcomes of species interactions thereby causing communities to change.
parasites can reduce survival or reproduction of their host
mycorrhizae
symbiotic associations between roots and various fungi
corals form mutalism with algae
they do. google it.
obligation with species specific
tropical figs and fig wasps
in mutualism
net benefits must exceed net costs for both partners
