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Evaluates the importance of biodiversity and the various services ecosystems provide to human society.
Imagine an airplane in mid-flight. If you pop out one rivet, the plane stays aloft. If you pop out fifty, the wings fall off. How many 'rivets'—or species—can our planet lose before the system crashes?
To manage ecosystems, we must first measure them. Biodiversity isn't just a count of species; it involves species richness (the number of different species) and species evenness (how close in numbers each species is). A forest with 100 oaks and 1 pine is less 'diverse' than a forest with 50 oaks and 50 pines. We use the Simpson’s Diversity Index () to calculate this. The value of ranges from 0 to 1, where 1 represents infinite diversity and 0 represents no diversity. The formula accounts for the probability that two individuals randomly selected from a sample will belong to the same species.
Let's calculate the diversity of a small pond with two species: 10 Bluegill and 20 Catfish.
Quick Check
If two ecosystems have the same number of species, but Ecosystem A is dominated by one species while Ecosystem B has equal numbers of all species, which has a higher Simpson's Index?
Answer
Ecosystem B has a higher index because it has greater species evenness.
Ecosystems are biological factories providing ecosystem services essential for human survival. We categorize these into four types: 1. Provisioning Services: Physical products like food, timber, and medicinal plants. 2. Regulating Services: Natural processes that act as 'buffers,' such as carbon sequestration, water purification by wetlands, and pollination. 3. Cultural Services: Non-material benefits including recreation, spiritual value, and aesthetic inspiration. 4. Supporting Services: The 'behind-the-scenes' processes that make all other services possible, such as nutrient cycling, soil formation, and primary production.
A mangrove forest provides multiple services simultaneously: 1. Provisioning: Local communities harvest fish and shrimp living in the roots. 2. Regulating: The dense roots break storm surges and protect the coastline from erosion. 3. Supporting: The forest traps sediment and cycles nitrogen, maintaining water quality. 4. Cultural: The area is used for eco-tourism and kayaking.
Quick Check
Is 'Photosynthesis' a provisioning service or a supporting service?
Answer
Supporting service, because it is a fundamental process (primary production) that enables all other services to exist.
Why does biodiversity matter for stability? The Insurance Hypothesis suggests that biodiversity acts as a safety net. In a highly diverse system, there is often functional redundancy—multiple species performing the same role (e.g., five different types of pollinators). If an environmental stressor, like a drought or disease, wipes out one species, others can step in to maintain the ecosystem's function. This ability to recover from disturbance is called resilience. Low-diversity systems (like agricultural monocultures) are fragile because they lack these 'backup' species.
Consider two plots of land facing a severe drought: 1. Plot A (Monoculture): Contains only Kentucky Bluegrass. The drought kills the grass, leading to soil erosion and total loss of productivity. 2. Plot B (Diverse Prairie): Contains 20 species of grasses and forbs. The shallow-rooted grasses die, but the deep-rooted legumes survive and thrive in the heat, maintaining soil nitrogen and preventing erosion.
Result: Plot B exhibits higher ecosystem stability due to the presence of drought-resistant functional traits.
Which of the following would result in the HIGHEST Simpson's Diversity Index ()?
A wetland filtering heavy metals out of runoff is an example of which service?
According to the Insurance Hypothesis, functional redundancy decreases the resilience of an ecosystem.
Review Tomorrow
In 24 hours, try to list the four categories of ecosystem services and provide one real-world example for each without looking at your notes.
Practice Activity
Find a patch of grass or a local park. Count the different types of plants in a 1x1 meter square and estimate their numbers. Try to calculate a rough Simpson's Index for that patch.