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Behavioural Ecology
Optimality
| Question | Answer |
|---|---|
| Optimality theory | Theory that seeks to describe how traits are optimal, i.e. they generate the most profitable ratio of fitness benefits to fitness costs |
| Optimality theory | It tries to understand / explain how animals (have evolved to) solve problems by simplifying into quantitative costs and benefits |
| Modelling theory | Problem: A fish has a fixed energy to spend on eggs Can spark 10 large eggs which each have a 50% chance of surviving Or 30 small eggs which have a 30% chance of surviving What will evolution favour? |
| Fitness benefit | FB = No. of eggs * probability of survival FBlarge = 10*0.5 = 5 < FBsmall = 30*0.3 = 9 |
| Are animals conscious calculators? | No - Evolution optimizes every organic trait, including behaviour, through natural selection Optimality can (sometimes) be quantified |
| The Ideal Free Distribution (IFD) | Rich habitat (many birds) vs poor habitat (low number of birds) Which habitat would it choose? The habitat that maximises survival/fitness (poor when rich is full/no more resources) |
| The Ideal Free Distribution (IFD) | Early arrivals to rich habitat have more resources and less competitors Late arrivals to rich habitat have less resources and more competitors - late should go to poor to maximise fitness |
| Assumptions of the Ideal Free Distribution | Its ideal, because animals have complete information about the availability of resources Its free, because animals are free to go where they will do best (not accounting for predation) |
| Assumptions of the Ideal Free Distribution | Under the ideal free scenario all individuals have equal fitness Therefore the IFD is a stable distribution |
| Stickleback experiment | In tank, hypothesised that twice as many fish would move to area with twice as much food (lag observed as fish caught up) At reduced food rate, less fish stayed At doubled food rate, more fish stayed |
| Living in groups: benefits | - Anti-predation - Inter-specific competition - Thermal advantage - Mobility advantage - Foraging efficiency |
| Living in groups: disadvantages | - Competition - Cuckoldry - Cannibalism/infanticide - Parasites & disease |
| Parasite transmission | ie. swallow colony size vs parasites per nest Parasitised nests have less fit, smaller offspring |
| Pathogens and population density | ie. Covid-19 spread more in densely populated areas |
| Example of benefit of group living | Sharing and increasing the vigilance load in Waterbuck - smaller groups spend less time being vigilant/more individual grazing - larger groups spend more time being vigilant |
| Example of benefit of group living | Antipredation in woodpigeons Flock size dictates attack success for goshawks predating woodpigeons |
| Marginal Value Theorem | Helps understand: 1) An animal exploits resources within discrete sites/patches 2) Within a patch, returns decrease over time (asymptotic (diminishing) gain curve) 3) There is a cost in getting to / from the patch |
| In starlings | Breeds in spring 400+ trips per day to feed nestlings Nestlings mainly get fed leatherjackets (larvae) How many leatherjackets should a parent bring back each trip? Currency: maximise the rate of deliver of food to nestlings Food/time taken |
| How much time should a starling parent take to forage? | More time spent searching, food becomes more scarce - also involves travel time (close or far) - add time taken to travel and time taken to forage |
| Formula | E (Ts) / Tt + Ts = R Tt = time spent travelling Ts = time spent searching R = rate |
| Scenarios | A = 3/(6+0.5)=0.46 B = 11/(6+9)=0.73 C= 9/(6+4)=0.90 - maximised |
| Does it hold up? | Hypothesis: as time travel increases, so should load size Yes!! |
| Copulating dung flies | Males mate with females on dung heaps The longer a male copulates, the more eggs he fertilises The longer a male copulates, the more opportunities he misses elsewhere |
| How long should a male copulate? | - to maximise rate of egg fertilisation - takes time to find other females, good to stay with one? |
| Optimality and resource selection: the economics of prey choice | Crab size and mussel size influence handling time - small/medium sized crabs take longer than large crabs to open mussels |
| Mussel calorific energy gain depends on handling time for different mussel and crab sizes | - large crabs use more energy quicker - smaller/medium crabs select mussels of optimal size |
| Are the crabs optimal? | Nearly compares to prediction, not matched but close |
| Optimality and resource selection: environmental predictability? How do animals behave to manage resources in unpredictable environments?? | Great tits - measured in morning (internal storage) In uncertain environments, weight gained In consistent enviornments, less weight Marsh tits - gained weight in both, no pattern, but externally stored resources |
| Marsh tits - why external storage? | Bird brain size? |
Created by:
reub8n
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