56.2

56.2 Biodiversity and Ecosystem Functioning

Overview

  • Biodiversity influences ecosystem organization, productivity, and resilience.

  • Key concepts examined include:

    • Organization of ecosystems affected by species diversity.

    • Productivity of ecosystems due to different species with various niches.

    • Resilience of ecosystems in response to natural disturbances.

Biodiversity Effects on Ecosystem Organization

  • Species diversity significantly impacts ecosystem structure.

  • Ecosystems with low species diversity may only have producers, while more diverse ecosystems can support various consumer levels:

    • Primary consumers

    • Secondary consumers

    • Tertiary consumers

  • Removal of keystone species can drastically alter ecosystem organization:

    • Example: Sea otters in North America.

      • Sea otters control sea urchin populations.

      • Without otters, sea urchins overconsume kelp, leading to habitat loss for young fish.

  • Decline in sea otter populations due to hunting resulted in increased sea urchins and reduced kelp forests:

    • Kelp forests provide habitat and protection for many marine species.

  • Threats remain for sea otters due to diseases that could cause further ecosystem reorganization.

Biodiversity Effects on Ecosystem Productivity

  • Ecosystem productivity refers to the total biomass produced by all producers in a year.

  • Studies show that higher species diversity correlates with increased producer biomass:

    • Researchers conducted experiments in Minnesota, manipulating grassland species diversity (0-32 species).

    • Results showed a dramatic increase in total biomass with more plant species until a plateau was reached.

    • Increasing species leads to a greater diversity of niches:

      • Some species thrive in high sunlight.

      • Others prosper in shade or different seasons (early spring vs. summer/fall).

      • Certain plants are better at accessing nutrients and water from various soil depths.

  • Mycorrhizal fungi also enhance productivity:

    • These fungi assist plants in nutrient uptake while benefiting from photosynthesis.

    • Studies show as fungal species increased, so did plant biomass and phosphorus extraction.

Biodiversity Effects on Ecosystem Resistance and Resilience

  • Resistance: the ability of an ecosystem to withstand environmental disturbances.

  • Resilience: the capacity to recover after disturbances.

  • Example from Minnesota grassland studies (11-year duration):

    • Plots with varying plant species (1 to 16 species) tracked insect species abundance.

    • Higher plant diversity corresponded to increased stability in herbivore numbers and predator/parasitoid species.

  • Implications for human-constructed ecosystems, like agriculture:

    • Traditional monoculture systems (single genotype) risk high vulnerability to pests/pathogens.

    • Higher genetic diversity in crops may offer a more stable agricultural yield.