Question

Which of the following species is most likely to have a Type III survivorship curve? a. humans, Homo sapiens b. common lizards, Zootoca vivipara c. thale cress plants, Arabidopsis thaliana d. lynx cats, Lynx canadensis

Short answer

The species most likely to have a Type III survivorship curve is c. thale cress plants, Arabidopsis thaliana, as they typically exhibit high juvenile mortality rates and low survival probability early in life, followed by higher survival probability in later stages.

Step-by-step solution

Understand the survivorship curves

Survivorship curves are used to display the proportion of individuals surviving at each age for a given species or group. There are three types of survivorship curves: 1. Type I - species with low juvenile mortality and high survival probability until old age, followed by a rapid decline in survival (e.g., humans). 2. Type II - species with constant mortality rates and survival probabilities across all ages (e.g., some birds and reptiles). 3. Type III - species with high juvenile mortality and low survival probability in the early stages of life, followed by a relatively higher survival probability in later stages of life (e.g., many plants, fish, and insects).

Analyze each species

We will analyze each provided species and assess which type of survivorship curve they most likely follow: a. humans, Homo sapiens: As mentioned earlier, humans typically follow a Type I survivorship curve, with low juvenile mortality and high survival probability until old age. b. common lizards, Zootoca vivipara: Most reptiles have a Type II survivorship curve, with a constant mortality rate across all ages. c. thale cress plants, Arabidopsis thaliana: Many plants exhibit a Type III survivorship curve, characterized by high juvenile mortality and low survival probability early in life, followed by higher survival probability in later stages. d. lynx cats, Lynx canadensis: Most mammals, like lynx cats, exhibit a Type I or Type II survivorship curve, characterized by low juvenile mortality rates and high survival probability over time.

Determine the species with a Type III survivorship curve

Given our analysis of the provided species, we can conclude that thale cress plants, Arabidopsis thaliana (option c), are most likely to exhibit a Type III survivorship curve. These plants typically have high juvenile mortality rates and low survival probability early in life, followed by higher survival probability in later stages.

Key concepts

Type III Survivorship

The Type III survivorship curve is a common model used in population ecology to describe certain species' life patterns. In this curve, the focus is on the dramatic decrease in population size due to high juvenile mortality. This means many individuals die soon after birth.
However, those who survive the early stages tend to live much longer.
This pattern is frequently observed among species like plants, fish, and insects.

Type III species generally produce a large number of offspring in hopes that a few will survive to adulthood.

• This is an evolutionary strategy to ensure that at least some of the offspring manage to overcome the challenges faced in the initial stages of life.
• Species like Arabidopsis thaliana (thale cress plants) exemplify this as they produce numerous seeds, but only a few mature into adult plants.

These species often adapt to unpredictable environments where the survival of offspring depends heavily on sheer numbers, rather than parental care.

Juvenile Mortality

Juvenile mortality is a term used to describe the high death rate among young individuals of a species, especially those following a Type III survivorship curve.
High juvenile mortality can be attributed to several factors:

• Environmental factors: Harsh conditions, predators, and limited food resources can increase the death toll among young individuals.
• Lack of parental care: Many species with Type III curves do not provide significant parental care to their offspring, exposing the young to higher risks.

As a result, only a small percentage of the original number of juveniles typically survives to maturity. Once these survivors reach a certain age, their likelihood of surviving into older age dramatically increases.

Survival Probability

Survival probability refers to the likelihood of surviving from one stage of life to the next. In species with a Type III survivorship curve, the survival probability is quite low during the early life stages.
However, this probability increases substantially once individuals reach adulthood.

Species that follow this curve tend to experience a 'bottleneck effect' whereby only those that survive the initial high-risk period have a much better chance of living into older age. This can have various causes:

• Natural selection: It ensures that only the fittest survive early life challenges, leading to a more resilient adult population.
• Adaptation and experience: The surviving individuals often develop adaptations or strategies to better cope with environmental pressures.

Understanding these factors is key to grasping why certain species adopt this strategy, ensuring the continuation of their genetic line despite early challenges.