GATE Ecology and Evolution Behavioural Ecology Syllabus

List the main sensory channels (modalities) of animal communication.

Chemical (olfactory/pheromonal), acoustic (sound), visual, tactile, and electrical communication.

What is a pheromone, and what are the two main types?

A pheromone is a chemical signal released by one individual that triggers a response in another of the same species. The two main types are releaser pheromones (immediate behavioural response, e.g., alarm, sex attractant) and primer pheromones (slow physiological/developmental changes, e.g., reproductive priming).

List key advantages and disadvantages of chemical signaling.

Advantages: travels around obstacles, persists over time, low energy cost, effective in darkness. Disadvantages: slow transmission, slow to fade (poor for rapidly changing messages), and limited directional information.

Give the characteristic advantages and disadvantages of acoustic signaling.

Advantages: rapid transmission, travels around obstacles and in darkness, can convey complex/rapidly changing information, and provides directional information. Disadvantages: high energy cost and easily intercepted by predators/eavesdroppers (conspicuous).

Why is sound attenuation and the choice of frequency important in acoustic signaling?

Low-frequency sounds attenuate less and travel farther through dense habitats (e.g., elephant infrasound, forest birds use lower pitches), whereas high frequencies attenuate quickly. Animals tune signal frequency to their habitat to maximize transmission (the acoustic adaptation hypothesis).

What are the trade-offs of visual signaling?

Advantages: fast, can be precisely directional, and can be rapidly switched on/off (e.g., posture, colour). Disadvantages: requires light/line of sight, blocked by obstacles, ineffective at night or in turbid water, and conspicuous to predators.

Distinguish a badge of status from a handicap signal.

A badge of status is a (often arbitrary) signal of dominance/fighting ability cheap to produce but maintained honest by social cost (e.g., bib size in house sparrows). A handicap signal is costly to produce and honest because only high-quality individuals can afford the cost (Zahavi's handicap principle, e.g., peacock train).

State Zahavi's handicap principle.

Signals are honest because they are costly: only high-quality individuals can afford to produce or bear an exaggerated, costly trait, so the cost guarantees the signal cannot be faked by low-quality individuals.

What is a recognition system in behavioural ecology?

The mechanism by which an animal identifies and classifies individuals or categories (kin, mates, species, group members) by matching perceived cues against a learned or innate template, then acting on the match.

Name the three components of a recognition system.

(1) Expression of cues/labels by the individual being recognized, (2) Perception and comparison of those cues against a template by the recognizer, and (3) Action/response based on the degree of match.

What are the two main mechanisms of kin recognition?

(1) Indirect/environmental cues such as spatial location ('whoever is in my nest') and association/familiarity, and (2) Direct phenotype matching, including comparison to self or known relatives, sometimes via 'green-beard' genetic recognition.

What is foraging behaviour?

The set of behaviours by which an animal searches for, captures, handles, and consumes food. It includes decisions about what to eat, where to feed, and how long to stay in a food patch.

What is Optimal Foraging Theory (OFT)?

A framework predicting that natural selection favours foraging strategies that maximize net energy (or fitness) gain per unit time, balancing energy gained against the costs and time of searching, handling, and predation risk.

In the optimal diet (prey choice) model, what determines whether a prey type should be included in the diet?

A prey type should be included if its profitability (energy/handling time, $E_i/h_i$) exceeds the overall expected rate of energy intake from continuing to search for and eat more profitable prey. Inclusion depends on encounter rate with higher-ranked prey, not on the prey's own abundance (the zero-one rule).

Define the profitability of a prey item in optimal foraging.

Profitability is the net energy gained per unit of handling time, $P_i = \dfrac{E_i}{h_i}$, where $E_i$ is the energy content and $h_i$ is the handling time of prey type $i$. Prey are ranked by profitability.

State the long-term rate of energy intake equation used in the optimal diet model.

For a forager encountering prey types at rates $\lambda_i$ with energy $E_i$ and handling time $h_i$, the rate of intake is $$R = \frac{\sum_i \lambda_i E_i}{1 + \sum_i \lambda_i h_i}$$ which selection acts to maximize.

What is the Marginal Value Theorem (MVT) and who proposed it?

Proposed by Eric Charnov (1976), the MVT predicts the optimal time to leave a depleting food patch: a forager should leave when the patch's instantaneous (marginal) intake rate drops to the average intake rate for the whole environment, maximizing overall gain given travel time between patches.

How does travel time between patches affect optimal patch residence time under the MVT?

Longer travel time between patches increases optimal residence time (the forager should stay longer in each patch), because the average environmental intake rate is lower, so it pays to deplete each patch further before leaving.

How is the optimal patch residence time found graphically in the Marginal Value Theorem?

By drawing a line from the origin point at the end of the travel-time axis tangent to the cumulative gain curve $g(t)$. The tangent point gives the optimal leaving time, where the patch's marginal gain rate equals the average rate (slope of the tangent).

What is the 'cost of sex' (the twofold cost)?

Sexual reproduction has a roughly twofold fitness disadvantage relative to asexual reproduction: a sexual female passes only half her genes to each offspring and (in anisogamous species) 'wastes' half the population producing males who don't bear young, so an asexual lineage can grow about twice as fast.

Besides the twofold cost of males, list other costs of sexual reproduction.

Recombination breaks up favourable gene combinations, the cost of finding/courting mates, risk of sexually transmitted diseases, predation risk during mating, and the energetic cost of producing courtship traits and gametes.

Name major hypotheses for why sex is maintained despite its costs.

The Red Queen hypothesis (sex generates variation to evade coevolving parasites), Muller's ratchet (sex purges deleterious mutations that accumulate irreversibly in asexual lineages), and the production of novel beneficial gene combinations to adapt to changing environments.

What is Muller's ratchet?

In asexual populations, deleterious mutations accumulate irreversibly because there is no recombination to recreate mutation-free genotypes once they are lost; the genome 'ratchets' toward ever-higher mutation loads. Sex/recombination halts this by reconstituting cleaner genomes.

What is sexual dimorphism?

Systematic differences in form, size, colour, or ornamentation between males and females of the same species, beyond the sex organs themselves. Examples include the peacock's train, the lion's mane, and larger male body size in elephant seals.

How does anisogamy relate to the origin of distinct sexes and sex differences?

Anisogamy is the production of gametes of unequal size: females produce few large, costly eggs and males produce many small, cheap sperm. This asymmetry in gamete investment underlies differing reproductive strategies, with females typically the choosier sex and males competing for mates.

State Bateman's principle.

Male reproductive success increases steeply with the number of mates (mating success), while female reproductive success is limited mainly by egg/offspring production and plateaus quickly. Hence males generally compete for mates and females are choosy.

What is mate choice and why is it usually exercised by females?

Mate choice is the selective preference of individuals for certain potential partners based on their traits. Because females typically invest more per offspring (anisogamy, parental care), they are the limiting sex and benefit most from choosing high-quality mates.

Distinguish direct from indirect (genetic) benefits in mate choice.

Direct benefits improve the chooser's own survival or fecundity (e.g., nuptial gifts, good territory, parental care, disease-free mate). Indirect benefits improve offspring genetic quality (e.g., 'good genes' for viability, or 'sexy sons' that inherit attractiveness).

Define sexual selection and name its two main mechanisms.

Sexual selection is selection arising from differential mating success. Its two mechanisms are intrasexual selection (competition among members of one sex, usually male-male combat) and intersexual selection (mate choice, usually females choosing among males).

Distinguish intrasexual from intersexual selection with examples.

Intrasexual selection is competition within one sex for access to mates, favouring weapons and large size (e.g., antlers, large male body size in elephant seals). Intersexual selection is mate choice by the opposite sex, favouring ornaments and displays (e.g., the peacock's train chosen by peahens).

Explain Fisher's runaway selection (the sexy son hypothesis).

A genetic correlation builds between a female preference for a male trait and the trait itself. Once both are coupled, the preference and the exaggerated trait reinforce each other and co-evolve at an accelerating ('runaway') rate, driving the trait far beyond its naturally selected optimum until checked by survival costs.

Contrast Fisher's runaway model with the 'good genes' (handicap) model of sexual selection.

In Fisher's runaway model the ornament is arbitrary and self-reinforcing through a preference-trait genetic correlation (attractiveness is the only benefit). In the good genes/handicap model the costly ornament honestly indicates heritable viability, so choosing females gain offspring with higher survival, not just attractiveness.