APES Video Notes 3.3 - Survivorship Curves

Summary

In this video, Mr. Speeds explains survivorship curves, building on concepts of R and K-selected species. He describes how these curves illustrate the survival rates of individuals within a cohort over time. The video outlines three types of survivorship: Type 1, with high survival rates due to parental care (e.g., humans); Type 2, showing steady mortality (e.g., birds); and Type 3, where high early mortality is offset by producing many offspring (e.g., insects). Mr. Speeds emphasizes the importance of understanding these trends for ecological studies and concludes with a call to practice data analysis of survivorship patterns.

Takeaways

• 😀 Survivorship curves illustrate the survival rates of a cohort of individuals of the same species over time.
• 📈 There are three main types of survivorship curves: Type I, Type II, and Type III, each reflecting different survival strategies.
• 👶 Type I species, such as humans and whales, experience high survivorship in early life, with rapid decline in old age due to high parental care.
• 🐦 Type II species, like birds and rodents, have a constant mortality rate throughout life, indicating moderate parental care and vulnerability to predation.
• 🌱 Type III species, including many insects and plants, exhibit high mortality rates in early life but can produce numerous offspring to offset low survivorship.
• 🧑‍🏫 The script emphasizes the importance of parental care in determining the survivorship type, with K-selected species showing Type I curves due to their nurturing behaviors.
• ⚖️ R-selected species, in contrast, produce many offspring with little to no care, leading to Type III curves characterized by high early mortality.
• 📊 The y-axis of survivorship graphs represents the number of individuals or proportion still alive, while the x-axis represents relative age.
• 📉 The slope of the curve indicates the rate of survival: a steep decline shows rapid mortality, while a gentle slope indicates higher survivorship.
• 📝 The practice application involves analyzing graphs of survivorship curves to identify trends and classify the type of survivorship represented.

Q & A

What is the main topic of the video?

The main topic of the video is survivorship curves, which relate to the survival rates of individuals within a species.

How do survivorship curves relate to R and K-selected species?

Survivorship curves illustrate how R-selected species, which produce many offspring with little care, typically show a type 3 survivorship curve, while K-selected species, which invest more parental care, show a type 1 survivorship curve.

What does the Y-axis represent in a survivorship curve graph?

The Y-axis represents the number of individuals or the proportion of individuals that are still alive at each age.

What are the three basic types of survivorship curves mentioned?

The three basic types of survivorship curves are Type I, Type II, and Type III.

Can you describe the characteristics of Type I survivorship?

Type I survivorship is characterized by high parental care, high survival rates in early and middle life, and a rapid decline in survivorship as old age sets in.

What types of organisms typically exhibit Type II survivorship?

Type II survivorship is typically seen in organisms like birds and rodents, which experience a steady decline in survivorship throughout their lives.

How do Type III species offset their high mortality rates?

Type III species, such as insects and plants, offset their high mortality rates by producing a large number of offspring, knowing that only a few will survive to adulthood.

Why is it important to understand the relative age in survivorship curves?

Understanding the relative age is important because it allows us to compare survivorship patterns across species with different lifespans without implying they live the same amount of time.

What practical exercise do students undertake in this lesson?

Students engage in data analysis to describe the trends in survivorship shown in a graph and justify which type of survivorship curve the data represents.

What example is given to illustrate K-selected species in the video?

An example of K-selected species given in the video is the mother grizzly bear, which fiercely protects her cubs.