91Ó°ÊÓ

A researcher has been tracking a population of turtles. The researcher marked 200 young turtles just after hatching. A year later, collection data reveal that about 80% survived. A year after that, collection data revealed that about 60% of the original group was still living. After a third year, about 40% could be found alive. What do these data say about the survivorship curve that would best describe this population? Explain your reasoning. a. Type II survivorship curve because the number of survivors decreases by the same value (20%) every year. b. Type I survivorship curve because the number of survivors decreases by the same value (20%) every year. c. Type II survivorship curve because the number of survivors increases by the same value (20%) every year. d. Type IV survivorship curve because the number of survivors decreases by the same value (20%) every year.

Step by step solution

01

- Understand the Problem

Determine what the different types of survivorship curves represent. There are three main types: Type I (high survival rate of the young, with most individuals dying at an older age), Type II (uniform rate of decline throughout life), and Type III (high mortality rate for the young with few individuals surviving to older age).

02

- Analyzing the Given Data

Interpret the given data: initially, there are 200 young turtles. After the first year, 80% survive meaning 200 * 0.8 = 160 turtles are alive. After two years, 60% of the original remains, which is 200 * 0.6 = 120 turtles. After three years, 40% of the original group remains alive, which is 200 * 0.4 = 80 turtles.

03

- Calculate the Yearly Decline

Recognize the pattern in the decline. Each year, there is a steady decrease of 20% of the initial population. Hence: First year: 200 - 160 = 40 turtles decrease (20% of 200),Second year: 160 - 120 = 40 turtles decrease (20% of 200), Third year: 120 - 80 = 40 turtles decrease (20% of 200).

04

- Determine the Appropriate Curve

Since the decrease of the population is uniform (20% of the original population each year), type II survivorship curve is characterized by a constant rate of mortality throughout life.

05

- Eliminate Wrong Choices

Review options: (a) matches the problem as Type II survivorship curve explains a constant mortality rate. (b) wrong because Type I curve suggests low mortality in young age and high mortality at older age. (c) wrong because increasing numbers do not fit the data, (d) wrong because Type IV is not a standard category and would not be used here.

06

- Choose the Correct Option

The best description of the data is given by option (a) Type II survivorship curve because of the constant annual mortality rate.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

survivorship curves

Survivorship curves are graphs that show the number of individuals of a species that survive at different ages. There are three main types: Type I, Type II, and Type III.

• Type I: Most individuals survive until old age, where mortality rate increases dramatically. An example is human populations in developed countries.
• Type II: This type shows a constant mortality rate throughout an organism's life. Birds and some reptiles often demonstrate this pattern.
• Type III: There is a high mortality rate for the young, but survivors after this initial period tend to live much longer. Many marine invertebrates and fish show this curve.

Each type reflects different strategies that organisms use to survive and reproduce in their environments.

population ecology

Population ecology is the study of how populations of species interact with their environment, including factors that affect population size, density, and growth.
Researchers examine various metrics to understand population dynamics, such as:

• Birth rates: Number of new individuals born.
• Death rates: Number of individuals that die.
• Immigration rates: Number of individuals moving into a population.
• Emigration rates: Number of individuals moving out of a population.

By analyzing these factors, ecologists can predict changes in population size and composition over time and make decisions about conservation and management.

turtle population study

A turtle population study involves tracking the survival and mortality rates of turtle populations over time.
In the given exercise:

• 200 young turtles were marked just after hatching.
• After one year, 80% (160 turtles) survived.
• After two years, 60% (120 turtles) survived.
• After three years, 40% (80 turtles) survived.

The observed data shows a steady annual decline, indicative of a Type II survivorship curve. Researchers use this data to understand the life cycle and threats faced by turtles, allowing them to develop strategies to protect them.

mortality rate analysis

Mortality rate analysis helps researchers understand how and why individuals in a population die. This is crucial for conservation and management efforts.
In the study of the turtle population, the mortality rate is consistent each year:

• 20% in the first year
• Another 20% (of the initial population) in the second year
• Yet another 20% in the third year

This consistent decline aligns with the characteristics of a Type II survivorship curve, which shows a constant mortality rate across different life stages. By analyzing these rates, scientists can identify specific life stages that may require additional protection and better understand the population's overall health.