Midterm Grades and Course Overview

• Midterm grades posted before the break

  • Access on Brockport portal

  • For E and P 202 course:

  • 50% lecture, 50% lab average

  • For School One:

  • Lecture grade up to this point

• Quiz scores not yet factored into final average

  • Slightly lower grades expected due to unrecorded quiz scores

Review of Key Concepts

Diadromous Fishes

• Definition: Fishes that migrate between freshwater and saltwater during their life cycle.

  • Includes anadromous and catadromous fishes

• Anadromous:

  • Born in freshwater

  • Migrate to saltwater

  • Return to freshwater to spawn

• Catadromous:

  • Born in saltwater

  • Live in freshwater

  • Return to saltwater to spawn

• Historical significance of eels as a species

  • Significant ecological and economic impact

  • Current population declines due to human-induced factors

Threats to Diadromous Fishes

Major Threats

• Dams as barriers to migration:

  • Impacts include:

  • Altered hydrology and organic matter movement

  • Obstruction of natural migration paths

  • Pollution preventing access to breeding areas

  • Temperature changes affecting survival

• Habitat destruction and biodiversity loss:

  • Increased human population density leading to habitat degradation

• Overfishing:

  • Economic and cultural factors driving consumption of migratory fishes

Implications of Dams on Ecosystems

Connectivity and Resilience

• Dams destroy connectivity among fish populations:

  • Impedes recolonization from upstream/downstream populations

  • Impacts the ability of populations to recover after disturbances

• Resilience defined:

  • The ability of populations to recover post-disturbance

• Removal of dams may initially lead to:

  • Increased abundance of species

  • Changes in sediment dynamics and habitats

Effects on Oceans and Nearshore Habitats

• Impact of barriers on marine ecosystems:

  • Disruption of migratory path of fish used as prey in marine food webs

  • Potential decrease in nutrients available in coastal marine habitats from decreased fish migrations

• Changes after dam removal include:

  • Altered flow and flooding dynamics

  • Increased diversity over time

  • Nutrient-rich sediments released downstream

Genetic Diversity and Inbreeding

Effects of Dams

• Dams reduce immigration, decreasing genetic diversity:

  • Leads to potential inbreeding and extinction risks

  • Isolation can lead to development of unique subspecies

Ecosystem Functions of Migrating Fishes

Ecosystem Subsidies

• Migratory fishes bring energy and nutrients from oceans to freshwater ecosystems:

  • Supports overall ecosystem productivity, nutrient cycling, and biodiversity

  • Key role in supporting diverse food webs through organic matter transfer

Law of the Minimum

Concept Overview

• Principle stating that the nutrient/resource in least supply limits primary production in ecosystems

• Related hypotheses:

  • Top-down control of primary production

  • Resource-based productivity understanding

• Limiting factor implications for:

  • Biodiversity, sustainability, and ecosystem health

Experimental Evidence

• Phosphorus as a key limiting factor in freshwater ecosystems:

  • Experiment demonstrated higher phytoplankton growth with added phosphorus

  • Evidence supports phosphorus as often limiting in North American lakes

• Connections to anthropogenic impacts on ecosystems:

  • Agricultural runoff contributing to nutrient loading in water bodies leading to algal blooms

Case Studies and Examples

Lake Erie

• Infamous for harmful algal blooms due to nutrient overload from agricultural runoff

  • Western Basin heavily impacted by Maumee River's drainage of agricultural land

  • Distinction between the health of western and eastern basins of Lake Erie

Coral Reefs and Oceanic Ecosystems

• Impacts of nutrient loading on coral reefs:

  • Excess nutrients can harm reef systems by promoting macroalgae growth

  • Disrupts necessary symbiotic relationships with corals

Key Scientists and Studies

• Important figures:

  • David Schindler: Noted for contributions to freshwater ecosystem research

  • Rachel Carson: Focused on environmental impact studies, related to limiting factors and ecosystem health

  Conclusion and Exam Preparation

• Recap on major concepts related to primary production:

  • Importance of phosphorus in freshwater and nitrogen in marine systems

• Avoiding excess nutrient eutrophication is vital for ecosystem health

• Sustainability and fisheries management critical for maintaining productive ecosystems