Habitat change or destruction Notes

What Causes a Habitat to Change?

1. A habitat changes when the physical or biological conditions that support life are altered.
2. When these conditions shift, the resources, niches, and interactions that species rely on are affected.
3. Even small changes can force organisms to move, adapt, or decline.
4. Habitat change can involve shifts in:
   1. Temperature
   2. Moisture
   3. Soil structure
   4. Vegetation cover
   5. Available space
   6. Interactions among species

Why Do Small Habitat Changes Cause Large Ecological Effects?

1. Ecosystems function as interdependent networks.
2. Changing one factor ripples outward.

Organisms rely on narrow tolerance ranges

1. Each species survives only within specific limits of temperature, light, moisture, and space.
2. Small shifts can:
   1. Restrict feeding or breeding areas
   2. Slow growth
   3. Increase stress and reduce survival

Species interactions magnify changes

1. When habitat conditions shift, food webs destabilize.
2. For instance:
   1. A slight drop in moisture reduces seed germination → fewer herbivores → fewer predators
   2. Reduced canopy cover changes shade levels → insect populations shift → affects bird nesting success

Keystone species amplify effects

1. Removing one keystone species can alter the entire habitat structure.
2. If a keystone species declines, dependent species also decline
3. The habitat changes structure following keystone loss

What Types of Habitat Change Occur?

1. Habitat change does not always mean destruction.
2. Even subtle shifts can alter ecological balance.
3. Habitat Loss
   1. The physical removal of an environment that organisms depend on.
   2. Losing forest canopy removes shade-dependent niches for insects, amphibians, and understory plants
4. Habitat Fragmentation
   1. A once-large habitat becomes divided into smaller, isolated patches.
   2. Causes include:
      1. Limited movement between populations
      2. Reduced genetic diversity
      3. Higher risk of local extinction
5. Habitat Degradation
   1. The habitat remains, but its quality declines.
   2. Causes include:
      1. Reduced vegetation structure
      2. Lower soil quality
      3. Disrupted microclimates (light, humidity, wind) Note: Degradation here excludes pollution, which is handled in a later chapter.
6. Habitat Shift
   1. Conditions change enough that the habitat transforms into a new type.
   2. Warming temperatures convert grasslands into shrublands as woody plants outcompete grasses

How Fast Can Ecosystems Recover From Change?

1. Factors influencing recovery include:
   1. Biodiversity: higher diversity provides more species able to fill empty niches, speeding recovery
   2. Reproductive rates: fast-reproducing species recolonize quickly (example: grasses recover faster than old-growth trees)
   3. Soil condition: healthy soil accelerates recovery; damaged soil slows it
   4. Remaining survivors: seeds, spores, burrowing animals, or dormant organisms jump-start recovery
   5. Disturbance severity: mild changes → quick recovery; severe changes → slow or incomplete recovery
   6. Disturbance frequency: frequent disturbances prevent full rebuilding

What Is Ecological Succession?

1. Succession describes how ecosystems rebuild after disturbance.
2. Secondary succession in particular, occurs when a habitat is disturbed but soil remains.

Why Do Some Ecosystems Recover Slowly or Not at All?

1. Some ecosystems have low resilience, especially those with:
   1. Highly specialized species
   2. Low biodiversity
   3. Complex food webs that collapse easily
   4. Slow-growing organisms
   5. Limited seed banks or regenerating organisms

How Does Habitat Change Affect Genetic Diversity?

1. Habitat change often reduces population sizes and isolates groups.
2. Consequences:
   1. Lower genetic diversity
   2. Reduced adaptability to new conditions
   3. Greater risk of harmful mutations increasing in frequency
   4. Higher extinction risk, especially in small populations