8. Following is the diagram of three idealized survivorship curves of animals.

Find the correct match between the group of animals and the respective survivorship curves.

(1) Marine pelagic fish and large mammals -lll and l, respectively

(2) Marine pelagic fish and large mammals- l and ll, respectively.
(3) Some birds and large mammals – l and lll, respectively.
(4) Marine pelagic fish and some birds – l and lll, respectively.

Matching Animal Groups to Survivorship Curves: Marine Pelagic Fish, Large Mammals, and Birds

Understanding how different animal groups survive and reproduce is fundamental to ecology. One powerful tool for visualizing these patterns is the survivorship curve, which plots the proportion of individuals in a population surviving at each age. There are three main types of survivorship curves—Type I, Type II, and Type III—each associated with distinct life history strategies and animal groups. This article explains these curves, matches them to the correct animal groups, and explores the ecological reasoning behind these patterns.

What Are Survivorship Curves?

Survivorship curves are graphs that show the proportion of individuals in a cohort (a group born at the same time) surviving from birth to each subsequent age. These curves help ecologists understand age-specific mortality and the life history strategies of different species.

The Three Main Types

• Type I (Convex) Curve:

  • Low mortality in early and middle life, with most deaths occurring in old age.

  • Typical of species with high parental care and few offspring, such as large mammals and humans.

• Type II (Diagonal) Curve:

  • Constant mortality rate throughout life.

  • Seen in species like some birds and rodents, where the risk of death is similar at all ages.

• Type III (Concave) Curve:

  • High mortality in early life, with those that survive to adulthood having a much lower risk of death.

  • Common in species that produce many offspring but provide little or no parental care, such as marine pelagic fish, insects, and most plants.

Matching Animal Groups to Survivorship Curves

Let’s examine the options provided and determine which matches are correct:

Option 1: Marine pelagic fish and large mammals – III and I, respectively

• Marine pelagic fish:

  • Produce vast numbers of offspring with little or no parental care.

  • Most offspring die early, but those that survive to adulthood have a high chance of living longer.

  • Survivorship curve: Type III.

• Large mammals:

  • Produce few offspring and provide extensive parental care.

  • Most individuals survive to adulthood, with most deaths occurring in old age.

  • Survivorship curve: Type I.

This match is correct.

Option 2: Marine pelagic fish and large mammals – I and II, respectively

• Marine pelagic fish:

  • Should be Type III, not Type I.

• Large mammals:

  • Should be Type I, not Type II.

This match is incorrect.

Option 3: Some birds and large mammals – I and III, respectively

• Some birds:

  • Typically show a Type II survivorship curve, with constant mortality throughout life, though some may approach Type I if parental care is very high.

• Large mammals:

  • Should be Type I, not Type III.

This match is incorrect.

Option 4: Marine pelagic fish and some birds – I and III, respectively

• Marine pelagic fish:

  • Should be Type III, not Type I.

• Some birds:

  • Should be Type II, not Type III.

This match is incorrect.

Why Do These Patterns Exist?

Marine Pelagic Fish: Type III Survivorship

Marine pelagic fish, such as herring, anchovy, and mackerel, release millions of eggs into the water. Most eggs and larvae are eaten by predators or die due to environmental challenges. Only a small fraction survive to adulthood, but those that do often live for several years and reproduce multiple times. This strategy is adaptive in the unpredictable and predator-rich open ocean.

Large Mammals: Type I Survivorship

Large mammals, such as elephants, whales, and humans, invest heavily in each offspring. They produce few young and provide extensive care, ensuring that most offspring survive to adulthood. Mortality is concentrated in old age, as adults are robust and well-protected. This strategy is adaptive in stable environments where resources are reliable and competition is high.

Birds: Type II Survivorship

Many birds, such as robins and sparrows, show a Type II survivorship curve, where the risk of death is relatively constant throughout life. This pattern reflects a balance between moderate parental care and environmental risks. However, some birds with very high parental care may approach a Type I curve, but the classic bird pattern is Type II.

Visualizing Survivorship Curves

A typical survivorship curve graph plots age on the x-axis and the proportion of survivors on the y-axis (often on a logarithmic scale):

• Type I: Starts high, remains high for most of the lifespan, then drops steeply at old age.

• Type II: Declines steadily in a straight line.

• Type III: Drops steeply at the beginning, then flattens out as survivors reach adulthood.

Ecological Significance

Understanding survivorship curves helps ecologists:

• Predict population dynamics: How populations grow, shrink, or recover from disturbances.

• Design conservation strategies: Protecting vulnerable life stages can have a large impact on population recovery.

• Understand species interactions: How competition, predation, and environmental factors shape life history strategies.

Real-World Examples

• Marine Pelagic Fish:

  • Mackerel, herring, and anchovy.

  • Millions of eggs, high early mortality, low adult mortality.

• Large Mammals:

  • Elephants, whales, and humans.

  • Few offspring, high parental care, low juvenile mortality.

• Birds:

  • Robins, sparrows, and kingfishers.

  • Moderate number of offspring, moderate parental care, constant mortality risk.

Summary Table

Why Are These Curves Important?

Survivorship curves summarize the survival and reproduction patterns of populations. They reveal the highest risk periods for mortality and help predict how populations will respond to environmental changes. For example, protecting adult marine pelagic fish is less critical for population recovery than protecting their spawning grounds, since most mortality occurs early in life. Conversely, for large mammals, protecting adults and juveniles is equally important, as most individuals survive to adulthood.

Conclusion

The correct match between animal groups and survivorship curves is:

(1) Marine pelagic fish and large mammals – III and I, respectively

This reflects the classic ecological patterns: marine pelagic fish exhibit a Type III survivorship curve due to high early mortality and low parental care, while large mammals show a Type I curve due to low early mortality and high parental investment. Understanding these patterns is essential for ecology, conservation, and wildlife management.