Summary Animal Ecology

Exam lectures
Food interactions
L1 & L2: foraging ecology
 Learn about key processes to:
- Describe the complexity of meeting nutrient and energy requirements
- Explain the main processes involved in food intake regulation
- Explain how animals procure food in their habitat



Foraging animal:

o What to eat & how much to eat?
o Where to go & how long to stay?



Digestion => break down ingested food, prior to absorption

 Consumers need energy, protein, minerals & vitamins
 2 problems:
- Cannot directly absorb most of energy
- Many cells to feed
 Gastrointestinal tract (GIT)
- Ingestion  digestion  absorption
- Carbs  simple sugar  abs
- Fats  glycerol & fatty acids  abs
- Proteins  aa  abs
- Vitamins  abs
- Minerals  abs
 2 sources of energy in foragers
- Cell contents (sugars, starches, fats)  rapidly digested (more in
browse plants)
- Cell wall (cellulose, lignin, hemicellulose)  slowly digested, lignin not
digested (more in grass plants)
 Strong seasonal effect on quality & quantity of grasses (don’t have to
know c3, c4)
 Jarman-Bell principle: body size
- Small animals have high mass specific requirements (per kg body
mass)
- Easily fermentable substances (sugars) yield more sugars per unit time
than cell walls (fibre)  small animals tend to be browsers, large
animals grazers
- Grass & browse food differently distributed: browse leaves scarce
 Ingesting sufficient browse is time consuming & requires selectivity 
small animals fit browsing niche better



Diet composition

,  Animals need to satisfy energy + various nutrients requirements
(proximate) for survival & repro (ultimate)
- Not 1 food contains all required substances
- Many food items contain undesirable substances
- Food items vary in availability & quality
- Most food substances need to be broken down after ingested &
reassembled inside body
- Animals compete with conspecifics & other species
- Animals try to avoid predation & diseases
- Food & consumer traits change through natural selection
 Animals adapt
- Morphological (e.g. body size, beak structure)
- Physiological (e.g. metabolic rate, GIT)
- Anatomical
- Metabolical
- Behavioural
 Compile suitable diet  maximise fitness



Selection & regulation of food intake

 Do animals select diet to obtain optimal intake nutrients & energy?
 Solution space
- > energetic requirement
- > vitamin/mineral req
- < rumen capacity
 Do animals regulate intake to obtain balanced diet?
 Contenders
- Optimal foraging theory => optimising currencies under constraints
(moose)
- Classical insect theory => self selection, conversions
- Geometric framework => multiple nutrient optimisation
- Ecological stoichiometry => flow based energy & nutrients balancing
- Satiation hypothesis => animals react to nutrients & toxins
 Satiation hypothesis
- Predation
- Cognitive mechanisms (avoid/prefer)
- Internal state (hungry)
- Predictions:
1. Varied diets are due to temporary food aversions due to flavours,
nutrients & toxins interacting along concentration gradients
2. Aversions should become more pronounced when food contains too
high levels of toxins or nutrient (imbalances)
3. Observed cyclic patterns of intake of different foods are due to
eating any food too often or too large amount
 Based on negative feedback mechanisms
 Review studies

, - Macronutrient specific food selection is linked to regulation of intake by
predators
- Wild predators select prey (parts) according to macronutrient
composition
 Changed foraging theory & applied wildlife conservation
 Herbivores, omnivores & predators balance nutrient intake
- Achieve homeostasis (proximate)
- Improve fitness (ultimate)



Functional response

 Curve flattens
 Core of prey selection theory
- Functional resp = instantaneous intake (g/min or g/s)
- Relationship between predator’s consumption rate & prey density
 Optimal foraging:
1. Decision: what to forage
2. Activity: search time (s)
3. Decision: pursue prey or not
4. Activities: handling time (h)
 Trade off: costs (time) vs gains (energy)
 Contingency model
- Pursue if E/h ≥ E/(s+h)
 Functional resp
- #consumed prey (P) per unit of time per predator on y
- As function of prey density (N) on x
- Type 1: h = 0 (filter feeders)
- Type 2: h >> 0 (single prey eaters)
- Type 3: s >> 0 (density dependent switching between prey species)
- Movement determines functional response
 Exp time (Exp(dt)) between encounters with immobile prey depends on
- Search velocity (s)
- Perception range (r)
- Prey density (N)
- Attack rate (a) = searching efficiency
 Exp(dt) = 1/2rsN = 1/aN

 Consumption rate = =
 Holling’s functional response
- Pe = #prey eaten/time
Type 1 = Pe = aN

Type 2 =

Type 3 =
 3 response types for predators with nutritiously adequate, discrete prey.
But for herbivores: