C
CraftExam
high importancemedium8 min

Patterns of Biodiversity: Latitudinal Gradient and Species-Area Relationship

Patterns of biodiversity are regular trends in species richness, especially the increase in diversity from poles to tropics and the increase in species number with sampled area, expressed by the species-area relationship.

Concept Practice Coming Soon

Learn the concept

Student-friendly explanation

Two major biodiversity patterns are important for exams. The latitudinal gradient shows that species richness generally increases from high latitudes towards the equator because tropical regions have had more stable climate, longer evolutionary time and greater solar energy input. The species-area relationship shows that larger areas usually contain more species because they include more habitats and niches. On a log scale, the relationship is written as log S = log C + Z log A, where S is species richness, A is area, C is a constant and Z is the slope. For very large areas, the slope becomes steeper.

How to write this in exams

  1. 1

    Start with the exact idea

    Patterns of biodiversity are regular trends in species richness, especially the increase in diversity from poles to tropics and the increase in species number with sampled area, expressed by the species-area relationship.

  2. 2

    Then show how to use it

    Identify whether the question is about latitude or area. For latitude, compare tropics and temperate or polar regions and give ecological reasons. For area, write the species-area equation, define S, A, C and Z, then explain that increasing area increases available niches and therefore species richness.

  3. 3

    Add one concrete example

    Tropical rainforests have far more species than temperate forests. A small island may have fewer bird species than a larger island because the larger island offers more habitat types and resources.

  4. 4

    Avoid this incomplete answer

    Writing that Z is species richness is wrong; Z is the slope of the line in the log-log species-area relationship.

Definition

Patterns of biodiversity are regular trends in species richness, especially the increase in diversity from poles to tropics and the increase in species number with sampled area, expressed by the species-area relationship.

Example

Tropical rainforests have far more species than temperate forests. A small island may have fewer bird species than a larger island because the larger island offers more habitat types and resources.

Rule to remember

Species-area relationship: log S = log C + Z log A. S means species richness, A means area, C is the y-intercept constant and Z is the slope of the line on a log-log plot.

Memory hook

Tropics are old, warm and stable; bigger area means more niches.

Examples and method

Worked example

If log S = log C + Z log A is given and the question asks what happens when area increases, state that species richness increases because a larger area usually includes more habitats, resources and ecological niches.

Method to apply

Identify whether the question is about latitude or area. For latitude, compare tropics and temperate or polar regions and give ecological reasons. For area, write the species-area equation, define S, A, C and Z, then explain that increasing area increases available niches and therefore species richness.

Diagram support

Diagram required: species-area curve and log-log straight line. Key labels: species richness on y-axis, area on x-axis, log S, log A, slope Z, intercept log C, steeper slope for very large regions.

How CBSE asks it

Asked as formula interpretation, graph labelling, reason for high tropical diversity, or assertion-reason linking stable tropical climate with greater species richness.

Avoid common mistakes

Common confusion

Students often remember the formula but forget what S, A, C and Z represent, or draw the species-area curve as a straight line on the normal scale without mentioning the log transformation.

Common wrong answer

Writing that Z is species richness is wrong; Z is the slope of the line in the log-log species-area relationship.

Exam tip

For species-area questions, always write the formula, define each symbol and mention that Alexander von Humboldt described the relationship between species richness and explored area.

Quick check

Why do tropical regions generally show higher species richness than temperate regions?

Tropical regions generally show higher species richness because they have had more stable climates, longer uninterrupted evolutionary time and high solar energy, which support more niches and speciation.

Answer writing and exam use

1-mark answer

State the pattern, write the species-area equation when relevant, define all symbols, draw or describe the graph with labelled axes, and add one reason such as habitat variety, stable climate or evolutionary time.

2-mark answer

State the pattern, write the species-area equation when relevant, define all symbols, draw or describe the graph with labelled axes, and add one reason such as habitat variety, stable climate or evolutionary time.

3-mark answer

State the pattern, write the species-area equation when relevant, define all symbols, draw or describe the graph with labelled axes, and add one reason such as habitat variety, stable climate or evolutionary time.
Practice

Concept practice is coming soon

Join the waitlist for concept-level MCQs and weak-concept practice.

10 MCQs5 MinutesInstant Results
Join Waitlist for Practice

Help improve this page

Found something confusing, incorrect, or missing?

Open Learning Map