4a. Organismal Ecology

coprophagy: ingestion of fecal material

apex predator: carnivore at the top of the food web

trophic cascade: an ecological phenomenon typically triggered by the addition or removal of top predators and changing the relative abundance of populations at various trophic levels

optimal foraging theory: organisms forage to maximize energy intake per unit time

generalist: consume a large portion of the prey they encounter

specialist: continue searching until encountering most profitable prey

  • all green plants get energy from sunlight
    • many adaptations to maximize exposure to sunlight + CO2 and minimize water loss
  • animals encounter thousands of possible food sources (ask ppl for this blank)
    • adaptations arguably ___
  • carbon fixed by plants provide the nutritional resources for all animals
    • directly/indirectly
  • plants and animals have different chemical composition
    • animals = high in fat and protein
    • plants = low in protein, high in carbohydrates
    • abundant in cellulose + lignin
    • especially difficult to break down
  • nitrogen = major part of protein
    • plants C:N = 50:1
    • animals C:N = 14:1

Herbivory

  • highest quality food for herbivores = high in protein (nitrogen)
    • nitrogen content increase? assimilation and retention time improves
    • nitrogen concentrated in new growth
    • nitrogen content in old growth is lower
  • natural selection has often timed birth to coincide with new growth
  • most ungulates give birth at the start of the growing season
    • ex. deer
    • good forage? good milk
  • insect larva usually develop round this time
  • food selection = interaction of quality, preference, and availability

Grazers and Browsers

  • grazers feed on leafy material

    • ex. grasses

  • browsers feed on woody material

  • both live on diets high in cellulose

    • depend on specialized bacteria living in the digestive tract
    • concentrate in the foregut/hindgut
Ruminants
  • highly specialized for cellulose digestion (foregut)
    • ex. cattle + deer
    • four-compartment stomach + very long
    • chew, pulp in rumen, regurgitate, rechew, reswallow
    • methane = by-product
    • contributes to climate change
Non-ruminant Herbivores
  • most digestion occurs in hindgut
    • ex. horses
    • simple stomachs, long intestines, cecum
  • easiest way to double length of digestive tract?
    • eat sh t
Lagomorphs
  • coprophagy
    • ex. rabbits + hares
    • crude fibre passes through as dry pellets
    • digestible material enters cecum for bacterial processing
    • expelled as soft green pellets
    • re-ingested for further processing
Herbivorous birds
  • three-chambered stomach
  • crop, proventriculus, gizzard
    • crop = storage
    • gizzard = grind up food
  • assist grinding by swallowing pebbles which can lead to lead poisoning

Carnivory

  • flesh of prey has same chemical composition as predator = easier digestion + assimilation
  • carnivore gets enough food? not malnourished
  • major problem = acquiring food
    • short intestines + simple stomachs
    • in hawks/owls, gizzard is reduced
    • gizzard acts as barrier against hair, bones, and feathers
    • regurgitates all this as pellets
  • apex predators
    • no predators of their own
    • role in maintaining ecosystem health
    • often of conservation concern
    • some responsible for trophic cascade
    • trophic cascades can result in dramatic changes in ecosystem structure and nutrient cycling

Omnivory

  • some studies show that it could stabilize food webs
  • food habits often vary with the seasons, reproduction, and growth rate
    • ex. black bear
    • eats buds, leaves, nuts, grubs, small-large mammals
  • facultative carnivore or omnivore?
    • no clearly defined ratio of plant to animal material to distinguish
  • optimal foraging theory molded by natural selection to enhance fitness
  • generalist vs specialist?
  • measuring prey profitability
    • calories per food item/ how long it takes to handle

Profitability of Food Items

  • E1/H1
    • E1 = energy content
    • H1 = capture, killing, eating, digestion
  • Classic Prey Choice Model
    • Eat if: E2/H2 > E1/(S1+H1)
    • Ignore if: E2/H2 < E1/(S1+H1)
  • according to OFT? forager should eat poorer item if while handling and eating it, forager cannot find a better food item
  • but forager should always eat _

summary

  1. Predators with handling times that are short compared to search times = generalists
  2. predators with handling times that are long relative to search time = specialists
  3. predators should have a broader diet in an unproductive environment