Demographic Stochasticity Causes Random Population Growth
Demographic stochasticity refers to random variations in population characteristics resulting from chance events in the survival and reproduction of individuals.
Understanding the Correct Option:
- Option 2 correctly identifies that the "discrete nature of births and deaths" is the reason for random variation. Each birth or death is an individual event. The precise timing and occurrence of these events are subject to chance, especially when the population is small. This randomness in individual fates leads to unpredictable fluctuations in the overall population size and growth rate, introducing uncertainty in population parameters like the birth rate ($b$) and death rate ($d$).
Why Other Options Are Incorrect:
- Option 1 relates to environmental stochasticity, where random changes in the environment (like weather) affect population growth, not the inherent biological events of individuals.
- Option 3 describes density-dependence, a mechanism where population growth rate changes predictably with population density, contrasting with the random nature of stochasticity.
- Option 4 mentions predictable time lags, which relate to deterministic population dynamics or cycles, not random chance variations.
Important Questions from Population growth curves
The population of whirligig beetles in a lake grows or declines exponentially i.e.
$N(t) = N(0)e^{rt}$
where $N(t)$ is the population size at time $t$, $N(0)$ is the initial population size and $r$ is the per capita rate of population change, occurring only due to birth and death.
A researcher tracks population sizes for a year and finds the following:Time interval Number of beetles at start Number of beetles at end January - March 1000 150 April – June 150 3013 July – September 3013 100 October - December 100 2009 Assuming that the individual birth rates remain constant throughout the year and only death rates are affected, which one or more of the following statements is/are true?
(In your calculations, round off the birth and date rates to two decimal places)- The population size at which net recruitment is the highest is also when the greatest amount can be harvested, while ensuring the long-term survival of the population. The amount harvested at this population size is known as
The graphs shown represent the relationship between population size ($N$) and population growth rate ($\frac{dN}{dt}$). Which one of the following growth curves represents a density-dependent population that experiences a strong Allee effect?
Overfishing reduced food availability for sea lions in California, causing a decline in their population size. In 1972, under the US Endangered Species Act, fishing was banned from sea lion foraging areas. Subsequently, the population of sea lions increased in a logistic form as shown in the figure.
The per capita growth rate is highest in the interval __________ and the population growth rate is highest in the interval __________
Consider the logistic population growth model, given by $$ \frac{dn}{dt} = rn \left(1 - \frac{n}{k}\right) $$ where $r$ is the intrinsic growth rate, $n$ is the population size and $k$ is the carrying capacity. Which one or more of the following is/are assumption(s) of the model?
