96. Which one of the following trait set characterizes best ar selected species?
    (1) Usually a type lll survivorship curve, short life spanand density dependent mortality
    (2) Usually a type l survivorship curve, short life span and density dependent mortality
    (3) Usually a type l survivorship curve, long life span and density independent mortality
    (4) Usually a type lll survivorship curve, short life span and density independent mortality

Introduction

In ecology, r-selected species are known for their rapid reproduction, short life spans, and ability to thrive in unpredictable environments. Their life-history traits are shaped by natural selection to maximize population growth in habitats where conditions are often unstable. Understanding these traits is crucial for distinguishing r-strategists from K-strategists and predicting population dynamics.

The Defining Traits of r-Selected Species

Type III Survivorship Curve

• r-Selected species typically exhibit a Type III survivorship curve. This means that most individuals die young, with only a few surviving to adulthood. This pattern is common in species that produce many small offspring and provide little or no parental care.

Short Life Span

• These species usually have short life spans, allowing them to reproduce quickly and take advantage of transient resources and opportunities.

Density-Independent Mortality

• Mortality in r-selected species is often density-independent, meaning that death rates are not strongly affected by population density. Instead, external factors such as weather, predation, or habitat disturbance play a larger role in survival.

Evaluating the Options

Let’s match these traits to the provided choices:

1. Usually a Type III survivorship curve, short life span and density dependent mortality

   • Incorrect. While Type III survivorship and short life span are correct, density-dependent mortality is not typical for r-selected species. Density dependence is more characteristic of K-selected species.

2. Usually a Type I survivorship curve, short life span and density dependent mortality

   • Incorrect. Type I survivorship is typical of K-selected species, not r-selected.

3. Usually a Type I survivorship curve, long life span and density independent mortality

   • Incorrect. This describes K-selected species, not r-selected.

4. Usually a Type III survivorship curve, short life span and density independent mortality

   • Correct. This option best describes r-selected species: they have a Type III survivorship curve, short life spans, and mortality that is largely density-independent.

Why These Traits Matter

• Population Dynamics: r-Selected species can quickly colonize new or disturbed habitats, but their populations often fluctuate wildly due to high juvenile mortality and external environmental factors.

• Ecological Role: These species are often the first to exploit new resources and play a key role in ecosystem recovery after disturbances.

Conclusion

The trait set that best characterizes r-selected species is:
Usually a Type III survivorship curve, short life span, and density independent mortality.

Correct answer:
(4) Usually a Type III survivorship curve, short life span and density independent mortality.