Chapter 18 - Lecture

Chapter 18: Primary and Secondary Production

Introduction

• Ecosystem ecology: Studies the flow of energy, water, and nutrients in ecosystems.

Primary Production Definitions

• Primary Production: Production of new organic matter per unit area in an ecosystem over a period of time.

• Gross Primary Production (GPP): Total amount of primary production by all primary producers.

• Net Primary Production (NPP): GPP minus respiration; biomass available to consumers.

• Secondary Production: Biomass production by consumers during a specific period.

Concept Overview

18.1: Terrestrial Primary Production

• Limited by:

  • Temperature: Higher rates in warm conditions.

  • Moisture: Correlation with primary production.

  • Nutrients: Essential for growth.

• Plants require optimal conditions for maximum production.

18.2: Aquatic Primary Production

• Generally limited by nutrient availability.

• Phosphorus: Controls phytoplankton biomass in freshwater ecosystems, significant in determining aquatic productivity.

Trophic Levels

• Trophic Level: Position in a food web based on energy transfer.

  • Primary Producers: First trophic level;

  • Primary Consumers: Second level (herbivores and detritivores);

  • Secondary Consumers: Third level (carnivores);

  • Tertiary Consumers: Fourth level.

Factors Influencing Primary Production

Terrestrial Patterns

• Temperature and Moisture: High correlation with productivity, highest in warm, moist conditions.

• Soil Fertility: Experimentation shows major impacts on production (e.g., fertilization effects on arctic tundra production).

Aquatic Patterns

• Importance of nutrient availability and freshwater ecosystems.

• Whole-lake experiments in Canada show substantial phytoplankton growth with nutrient additions.

• Marine: Concentrated productivity in areas of nutrient availability, especially along continental margins and in upwelling zones.

• Nutrient Enrichment: Studies indicate nitrogen as a limiting nutrient, impacting primary production in aquatic environments.

Primary Producer Diversity

• Increased diversity leads to higher primary production.

• Tilman et al. (2001): Understanding how plant functional groups affect productivity and richness.

• Aquatic ecosystems: More species richness correlates with higher primary production, confirmed by studies from Cardinale (2011).

Consumer Influence on Primary Production

Trophic Cascades

• Bottom-up controls: Physical and chemical factors influence ecosystems.

• Top-down controls: Effects of consumers on production levels.

• Piscivorous and planktivorous fish impact primary productivity in lakes via trophic cascades.

Grazing Effects

• Serengeti: Grazers consume substantial primary production, promoting growth in grasses.

• Compensatory Growth: Occurs at intermediate grazing levels, enhancing production while heavy grazing can inhibit recovery.

Secondary Production

Ecosystem Relationships

• Higher primary production correlates with higher secondary production.

• Energy Transfer: Energy loss occurs at each trophic level.

• Ecological Efficiency: Percentage of energy transferred across levels varies, impacting overall productivity.

Estimation Techniques

• Benke’s approach: Following cohorts over time to estimate secondary production.

• Models: Predict relationships between primary and secondary production based on predator-prey dynamics.

  • Prey-dependent model: Increased primary production affects predator abundance, no change in primary consumers.

  • Ratio-dependent model: Increased primary production leads to increases in both primary and secondary consumers.