Heterotrophs

heterotrophy

organic sources of carbon synthesized by others to derive energy - eat organic material

found across all groups: prokaryotes, protists, plants, fungi, animals

can be: herbivores, carnivores, or detritivores

must balance ease of getting food and quality

herbivores

organisms which eat plants

high ease, low quality (too high CN)

high CN means hard to ingest and digest, needs many adaptations and relationship w symbionts

must eat a lot

koala example

eat a lot to compensate for low quality food

long digestive system, gut microbes, and sleep a lot

herbivore adaptation

in order to gain max nutrients from plants

insect mandibles for slicing and manipulation, rodents long incisors to gnaw tough material, ruminants complex digestive system

herbivory challenges

plant defences such as physical (thorns), chemical (cyanide)

but animals can adapt to these - such as caterpillars resistance to cardiac glycosides, or giraffes long tongue to thorns

carnivores

organisms which eat animals

high quality food (high CN), but harder to get food

most prey species give same nutrition

little digestive adaptations, but selection for efficiency

carnivory adaptations

speed, claws or talons, canine teeth

detritivores

organisms which ingest and digest dead organic matter via internal processes - all are decomposers

easy to get food but quality is variable (plant material has low quality, feces or dead animals have slightly higher, etc)

very important in decomp and nutrient cycling

detritivores limitations

not limited by abundance but by abiotic factors and chemical composition

ex soil moisture is very important for soil dwelling organisms

nitrogen use efficiency

plants are able to reabsorb nitrogen before dropping leaves

this affects CN ratio in dead material

decomposers

do not ingest dead organic matter but can directly absorb nutrients through chemical and biological processes

not all are detritivores

ex fungi, slime mold

food quality

balance of 5 elements which make up biomass or organisms

carbon (structure), oxygen (water), hydrogen (water), nitrogen (amino/nucleic acids), and phosphorus (cellular processes, ATP)

relative abundance of C and N

plants have high ratio, nitrogen is limiting

animals have low ratio, carbon is limiting

indicates what type and how much one needs to consume

mixotrophy

gain energy from photosynthesis and consuming organic material

includes algae, bacteria and protist species, as well as hemi-parasitic plants (obtain food from living host) and carnivorous plants

omnivores

gain energy from both plant and animal matter

myco-heterotroph plants

pine-sap and ghost pipe

no photosynthesis (chloroplasts), instead are associated with and obtain food from fungal hyphae via myccorhizae

epiphytes

grow on other plants but don’t parasitize on them

not even mixotroph

just grow on them for better access to resources

insectivorous plants

obtain additional nutrients from trapped insects

still photosynthesize

energy limits

in plants photosynthesis reaches a plateau above Isat

in animals in saturates at a specific density - functional response curves

what influences organism feeding rate

physical ability, time to digest, time to find food, time to handle/process food, consider safety which searching

all use energy or are invested energy

functional response curve type 1

least common

feeding rate increases linearly due to quick food processing

but then food level abruptly levels off

ex zooplankton, filter feeders

mostly restricted by density of food they are eating

functional response curve type 2

feeding rate increases linearly at low food density and slows through moderate and levels off

limited. by searching for food as well as handling times at low density

ex moose, wolves, bears, parasitoid wasps

functional response curve type 3

s shaped feeding rate - increases rapidly

limited by age, exposure to prey and encounter rate

ex juveniles learning to hunt, prey switching, or searching for rare prey

optimal foraging strategy

describes how organisms feed as an optimizing process - maximizes or minimizes some quantity such as energy intake or predation risk

what, when, where

marginal value theorem

an organism should spend time in a patch that maximizes their energy gained in the patch

when energy gain levels off they should leave the patch

longer travels time = more time spent in

net energy gain

gain from one prey species including time spent, energy gain, number of prey encountered per unit time, energy lost searching and handling time

can be altered to include n species

a species can be predicted to prey on one species if the energy gain is more than the energy lost searching for more species (etc)

ex bluegill sunfish

most abundant prey are 1mm long

optimal foraging theory predicts 4 mm long max energy rate

actual intake from prey is 4mm as seen in natural habitat

optimal foraging by plants

limited by nutrients in soil, water and sunlight - while they are sessile, they can grown to locations of these factors

roots grow down with gravity (positive gravitropism), they also branch and use root hairs

thigmotaxis

response of an organism to touch

ex, searching for climbing surface to reach light

not all plants, but ex legumes