Chapter 6 Practical 3
Aim:
To depict and analyze the global patterns of biodiversity distribution across latitudinal and altitudinal gradients.
Principle:
Biodiversity is not uniformly distributed across the Earth. Two of the most fundamental and predictable patterns are:
Latitudinal Diversity Gradient: Species richness (the number of species in an area) is highest in the tropics (near the equator) and decreases steadily towards the poles. This is considered one of the most robust patterns in ecology.
Altitudinal Diversity Gradient: Similarly, on a mountain, species richness is highest at the base (low altitudes) and decreases towards the summit (high altitudes). This pattern mirrors the latitudinal gradient on a smaller scale.
Primary Drivers of these Patterns:
Solar Energy and Climate: The tropics receive more consistent solar energy, leading to higher productivity, warmer temperatures, and longer growing seasons, which support more species.
Stability: Tropical regions have experienced less climatic upheaval (like glaciations) over geological time, allowing for longer evolutionary periods and greater speciation.
Spatial Heterogeneity: Tropical and lowland areas often have more complex habitats, providing more niches for species to exploit.
Area: The tropical zone is the largest biogeographical region on Earth.
Materials Required:
Computer with internet access.
Spreadsheet software (MS Excel / Google Sheets).
Data from online biodiversity databases (GBIF, IUCN).
Graphing and visualization tools.
Procedure:
Part A: Depicting the Latitudinal Gradient
Data Collection:
Visit the Global Biodiversity Information Facility (GBIF) website (www.gbif.org).
Use the "Occurrence search" feature. Select a well-studied, widely distributed taxonomic group (e.g., Birds, Mammals, or Amphibians).
Download data for a large number of records (e.g., 10,000 records) or use the built-in mapping tools.
Data Analysis:
If using raw data, in your spreadsheet, create a column for "Latitude" (or use the "Decimal Latitude" field).
Create a frequency table: Count the number of unique species records in latitudinal bands (e.g., 0°-10°, 10°-20°N, 10°-20°S, etc.).
Alternatively, use GBIF's interactive map to visually observe the density of records. The highest density will be evident in tropical regions.
"Go to taxonomy > Group by species > count number of species"
Visualization:
Create a Scatter Plot:
X-axis: Latitude (from -90° South to 90° North).
Y-axis: Number of Species Records (or Species Richness if data permits).
The resulting plot will show a prominent hump, peaking near the equator (0° latitude).
Part B: Depicting the Altitudinal Gradient
Data Collection:
Choose a specific mountain range (e.g., the Himalayas, the Andes, or the Western Ghats).
Research secondary data from scientific literature or databases like GBIF or NCBI.
" Navigate to the Occurrences search page on the GBIF website (
gbif.org/occurrence/search).Use the Filters menu on the left side of the page to refine your search.
Click the Advanced tab to reveal more specialized filters. (latitude 0 to 40 to cover India region > add)
Enter a minimum and maximum value for the Elevation filter (in meters above sea level) to define your altitude range.
Refine your search further by adding other filters, such as a specific species, a higher taxonomic group (e.g., family or genus), a country, or a date range.Click Download once your filters are set. GBIF will process your request and provide a downloadable dataset, which you can use for your analysis"
Find a study or dataset that lists species richness for a specific taxon (e.g., birds, plants) at different elevation zones (e.g., 0-500m, 500-1000m, 1000-1500m, etc.).
Data Analysis:
Compile the data into a simple table with two columns: "Altitude Zone (m)" and "Number of Species."
Visualization:
Create a Line Graph or Bar Chart:
X-axis: Altitude / Elevation (in meters).
Y-axis: Number of Species.
The graph will show a curve where species richness is highest at lower elevations and declines as altitude increases.
Observations:
Table 1: Hypothetical Data Showing Latitudinal Gradient for Bird Species (Based on GBIF data trends)
| Latitudinal Band | Approx. Number of Bird Species Recorded |
|---|---|
| 0° - 10° (Tropics) | 950 |
| 10° - 20° | 800 |
| 20° - 30° | 650 |
| 30° - 40° | 500 |
| 40° - 50° | 350 |
| 50° - 60° | 200 |
| 60° - 70° | 100 |
| 70° - 80° | 50 |
| 80° - 90° (Poles) | 20 |
Graph 1: Latitudinal Diversity Gradient (Birds)
*(A hand-drawn or printed graph based on the table above would be inserted here, showing a strong peak at 0°)*
Table 2: Hypothetical Data from a Study in the Himalayas Showing Altitudinal Gradient for Plant Species
| Altitude Zone (meters) | Approx. Number of Plant Species |
|---|---|
| 500 - 1000 | 400 |
| 1000 - 1500 | 350 |
| 1500 - 2000 | 300 |
| 2000 - 2500 | 220 |
| 2500 - 3000 | 150 |
| 3000 - 3500 | 80 |
| 3500 - 4000 | 40 |
Graph 2: Altitudinal Diversity Gradient (Himalayan Plants)
(A hand-drawn or printed graph based on the table above would be inserted here, showing a steady decline with altitude)
Result:
The analysis of secondary data clearly depicts the two major ecological patterns:
Latitudinal Gradient: Biodiversity, as represented by bird species records, is highest in the tropical latitudinal band (0°-10°) and shows a steady decrease towards the polar regions.
Altitudinal Gradient: Biodiversity, as represented by plant species in a mountain range, is highest at the lowest altitude band (500-1000m) and decreases progressively towards the higher altitudes.
Discussion:
The observed patterns align perfectly with established ecological theory. The results can be attributed to:
Higher energy input (solar radiation) at lower latitudes and altitudes.
Greater environmental stability and reduced seasonality in the tropics.
Historical factors like less disruption from past ice ages in tropical regions.
Exceptions: Some taxa, like penguins, are adapted to polar environments and show a reverse gradient. In some dry mountains, peak diversity might occur at mid-elevations due to cloud forests and optimal moisture levels.
Implications: Understanding these gradients is crucial for conservation planning. The tropics, being biodiversity hotspots, require urgent and focused conservation efforts.
Conclusion:
This practical demonstrates the profound and predictable influence of geographic gradients—specifically latitude and altitude—on the distribution of global biodiversity. By visualizing data from open-access repositories, we can confirm fundamental ecological principles that are vital for understanding and conserving the natural world.
Viva Voce Questions:
What is the Latitudinal Diversity Gradient?
It is the pattern of increasing species richness from the poles to the equator.
Why are there more species in the tropics?
Due to higher solar energy, greater climatic stability, and more complex habitats over evolutionary time.
Does the altitudinal gradient always show a linear decrease?
No, in some cases, diversity can peak at mid-altitudes due to factors like the presence of cloud forests which provide high moisture and moderate temperatures.
Name one exception to the latitudinal gradient.
Marine biodiversity for some groups, like seals or penguins, is higher in colder polar waters.
What is the significance of studying these patterns?
It helps identify biodiversity hotspots, predict the impacts of climate change on species ranges, and prioritize areas for conservation.
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