Insect Apocalypse Lecture 9 - Losing their home – Habitat loss

BSCI 144 Insect Apocalypse Lecture 9: Habitat Loss Notes

Overview of Habitat Loss

• Habitat loss significantly impacts species, particularly the Baltimore Checkerspot butterfly (Euphydryas phaeton), which is endangered in Maryland.

Urbanization Trends

• As global population increases, key needs include:
  • Food
  • Fresh water
  • Housing
• Urbanization vs. Rural Population:
  • 1800: ~5% urban
  • 2000: ~80% urban
• Notable urbanization statistics:
  • California: Most urbanized state
  • Maryland: 14th
  • Maine: Least urbanized
• Global trends show that America, Eurasia, and Australia are among the most urbanized regions globally.

Shifts from Natural Habitats to Urban Settings

• The Eastern Deciduous Forest undergoes a Subtraction Experiment:
  • Diverse natural forests transform into less diverse farms.
  • Farms further develop into housing developments, which may vary in diversity.
  • Housing developments can eventually convert to less diverse urban centers dominated by hardscape.
• Hardscape adversely affects plant life by denying water, leading to reduced forest cover as urbanization progresses:
  • Woodland → Farmland → Open Species → Residential → Offices → City Centers

Insect Fundamental Needs and Dependency on Plants

• Insects rely on:
  • Food
  • Fresh water
  • Habitat
• Plants serve as the foundation of food webs, impacting biodiversity:
  • Insect herbivores often have specialized diets, feeding on specific plant genera or families.

Key Terminology

• Species Richness: The total number of species in a given area.
• Abundance: The number of individuals within a species.

Effects of Urbanization on Plant Diversity and Insect Biodiversity

• Urbanization Gradient Impact on Plant Diversity:
  • Residential Areas:
  • Density: 69,000 plants/km²
  • Diversity: > 100 species
  • City Streets:
  • Density: 48 plants/km²
  • Diversity: 30 species
• Research indicates that declining plant biodiversity may lead to declines in insect biodiversity.

Case Studies on Insect Decline

• Michael Staab et al., 2023:
  • Study on flying insects in Germany across 140 sites from 2008-2017.
  • Higher harvesting intensity negatively affected:
  • Species abundance
  • Herbivore abundance
  • Omnivore richness and abundance
• Ground beetles (Carabidae) meta-analysis:
  • Urban environments exhibit a significant decline in species richness (77.6% of rural richness) and abundance (63.7% of rural abundances).
  • Large beetle populations and predatory beetles decreased significantly with urbanization.

Consequences of Insect Declines

• As populations of large ground beetles, crucial predators, decline, the impact on caterpillar populations may become notable.
• Non-native plant species increase along urbanization gradients, which can affect herbivore relationships:
  • Native plants support native herbivores, while non-native plants often fail to do so.

Importance of Native Plants

• Biodiversity benefits from native plants include:
  • Higher herbivore populations
  • Increased butterfly and bird diversity
• Arthropod Community Composition Study (Shrewsbury et al., 2009):
  • Findings indicate that native landscapes support more chewing herbivores compared to non-native ones, while non-native landscapes have greater populations of sucking herbivores.