GATE Ecology and Evolution Ecology Syllabus

In a life table, what do the symbols $l_x$ and $m_x$ represent?

$l_x$ is survivorship: the proportion of the original cohort surviving to age $x$. $m_x$ (or $b_x$) is the age-specific fecundity: the average number of offspring produced per individual of age $x$.

Write the formula for net reproductive rate $R_0$ from a life table and interpret it.

$$R_0 = \sum_x l_x m_x$$ It is the average number of offspring per individual per generation. $R_0 > 1$ means growth, $R_0 = 1$ replacement, $R_0 < 1$ decline.

Name the three idealized survivorship curve types and give an example organism for each.

Type I (low juvenile mortality, high late mortality — e.g., humans, large mammals); Type II (constant mortality across ages — e.g., many birds, rodents); Type III (high juvenile mortality, few survive to adulthood — e.g., many fish, invertebrates, plants).

Define mutualism and give an example.

Mutualism (+/+) is an interaction benefiting both species. Example: mycorrhizae between fungi and plant roots, or pollination of flowers by bees.

Distinguish symbiosis from mutualism.

Symbiosis is any close, long-term physical association between two species (it can be mutualistic, commensal, or parasitic). Mutualism specifically refers to associations where both partners benefit; thus mutualism is one form of symbiosis.

Define commensalism with an example.

Commensalism (+/0) is an interaction where one species benefits and the other is unaffected. Example: epiphytic orchids growing on tree branches, or barnacles attached to a whale.

Define parasitism and contrast it with predation.

Parasitism (+/-) is an interaction where the parasite benefits at the host's expense, usually without immediately killing it and living on/in it. Predation (+/-) involves a predator killing and consuming prey. Parasites are typically smaller than hosts.

Summarize the signs (+, -, 0) for the main interspecific interactions: competition, predation/parasitism, mutualism, commensalism, amensalism, neutralism.

Competition (-/-); Predation & Parasitism (+/-); Mutualism (+/+); Commensalism (+/0); Amensalism (-/0); Neutralism (0/0).

State the competitive exclusion principle (Gause's principle).

Two species competing for the exact same limiting resource cannot coexist indefinitely at constant population values; the more efficient competitor will exclude the other. Complete competitors cannot coexist.

Distinguish interference competition from exploitative (resource) competition.

Interference competition involves direct antagonistic interaction (e.g., aggression, allelopathy, territoriality) preventing access to resources. Exploitative competition is indirect, occurring through depletion of a shared limiting resource.

What is resource partitioning and how does it relate to coexistence?

Resource partitioning is the differential use of resources (in space, time, or type) by competing species, reducing niche overlap and allowing coexistence by avoiding competitive exclusion. It can drive character displacement.

Write the Lotka–Volterra predator–prey equations and define the parameters.

$$\frac{dN}{dt} = \alpha N - \beta NH, \qquad \frac{dH}{dt} = \delta \beta NH - \gamma H$$ where $N$ = prey, $H$ = predator, $\alpha$ = prey growth rate, $\beta$ = predation rate, $\delta$ = conversion efficiency, $\gamma$ = predator death rate.

What characteristic dynamic do the Lotka–Volterra predator–prey equations produce?

Coupled, out-of-phase oscillations (cycles): predator peaks lag behind prey peaks. The populations cycle around a neutral equilibrium, with predator abundance trailing prey abundance by roughly a quarter cycle.

Give the equilibrium (isocline) point values of the Lotka–Volterra predator–prey model.

Prey nullcline gives predator equilibrium $H^* = \frac{\alpha}{\beta}$; predator nullcline gives prey equilibrium $N^* = \frac{\gamma}{\delta\beta}$. The two nullclines intersect at this neutral equilibrium.

Write the Lotka–Volterra competition equations for two species.

$$\frac{dN_1}{dt} = r_1 N_1\left(\frac{K_1 - N_1 - \alpha_{12}N_2}{K_1}\right), \quad \frac{dN_2}{dt} = r_2 N_2\left(\frac{K_2 - N_2 - \alpha_{21}N_1}{K_2}\right)$$ where $\alpha_{12}, \alpha_{21}$ are competition coefficients.

State the condition for stable coexistence in the Lotka–Volterra competition model.

Stable coexistence occurs when interspecific competition is weaker than intraspecific competition for both species: $K_1 < \frac{K_2}{\alpha_{21}}$ and $K_2 < \frac{K_1}{\alpha_{12}}$ (i.e., $\alpha_{12}\alpha_{21} < 1$).

Define a functional response and name Holling's three types.

A functional response describes how a predator's per-capita prey consumption rate changes with prey density. Type I: linear; Type II: decelerating to a plateau (handling-time limited); Type III: sigmoidal (S-shaped, with prey switching/learning).

What is ecophysiology (physiological ecology)?

Ecophysiology is the study of how organisms' physiological functions and adaptations respond to and are shaped by abiotic environmental factors (temperature, water, light, salinity, oxygen), linking physiology to ecological distribution and performance.

Distinguish poikilotherms/ectotherms from homeotherms/endotherms.

Ectotherms (poikilotherms) rely on external heat sources and have variable body temperature (e.g., reptiles, fish). Endotherms (homeotherms) generate metabolic heat to maintain a constant body temperature (e.g., birds, mammals).

State Bergmann's rule.

Among endothermic (warm-blooded) species or populations, those in colder climates tend to have larger body size, reducing the surface-area-to-volume ratio and conserving heat.

State Allen's rule.

Endotherms in colder climates tend to have shorter appendages (ears, limbs, tails) relative to body size, minimizing surface area and heat loss; those in warmer climates have longer appendages.

Distinguish osmoconformers from osmoregulators.

Osmoconformers keep their internal osmolarity equal to that of the surrounding medium (e.g., most marine invertebrates). Osmoregulators actively maintain internal osmolarity different from the environment (e.g., freshwater fish, marine teleosts).

Name plant adaptations to water availability: xerophytes, mesophytes, hydrophytes.

Xerophytes are adapted to dry/arid conditions (thick cuticle, reduced leaves, water storage, e.g., cacti). Mesophytes grow in moderate moisture. Hydrophytes are adapted to aquatic or waterlogged habitats (aerenchyma, reduced roots).

What is the difference between C3, C4, and CAM photosynthetic adaptations regarding abiotic stress?

C3 plants fix carbon directly (efficient in cool, moist, low-light). C4 plants concentrate $\ce{CO2}$ spatially, reducing photorespiration in hot, high-light environments. CAM plants open stomata at night to conserve water in arid habitats.

Define ecological succession.

Ecological succession is the gradual, directional, and predictable change in the species composition and structure of a community over time, following a disturbance or the creation of new habitat, culminating in a climax community.

Distinguish primary from secondary succession.

Primary succession begins on a lifeless substrate with no pre-existing soil (e.g., bare rock, lava flow, glacial till), starting with pioneer species. Secondary succession occurs where a disturbance removed the community but soil and some organisms remain (e.g., after fire or abandoned farmland).

What are pioneer species and a climax community?

Pioneer species are the first colonizers of a newly available or disturbed habitat (often hardy, fast-growing, e.g., lichens, mosses). The climax community is the relatively stable, self-perpetuating endpoint of succession in equilibrium with the regional climate.

Name the three classical models of succession mechanisms (Connell & Slatyer).

Facilitation (early species modify the environment making it suitable for later species), Tolerance (later species succeed regardless of earlier ones, tolerating conditions), and Inhibition (early species inhibit colonization by later ones until they are removed).

What is community assembly, and what role do assembly rules and filters play?

Community assembly is the process by which species colonize and organize into a local community from a regional species pool. Abiotic filters (environmental tolerances) and biotic filters (competition, predation), along with dispersal limitation, sequentially screen which species can establish.

What is a keystone species, and how does it relate to community organization?

A keystone species exerts an effect on community structure disproportionately large relative to its abundance. Its removal causes major changes in diversity and organization (e.g., Pisaster sea star controlling intertidal community structure in Paine's experiments).