Introduction to Ecology (Marine Biology)

Introduction to Ecology: Principles and Scopes

• Definition of Ecology: Ecology is defined as the scientific study of the processes that influence the distribution and abundance of organisms. It also encompasses the interactions among organisms and the transformation and flow of energy and matter within biological systems.

• Context within the Tree of Life: Ecology focuses on the biological context of "who" resides within the environment and how they function.

• The Five W's of Ecology: Based on Aristotle's Nicomachean Ethics, ecology addresses five fundamental questions:

  • Who: The specific organisms involved.

  • What: The nature of the biological processes.

  • Where: The spatial distribution of organisms.

  • When: The temporal distribution and timing of events.

  • Why/How: The causal mechanisms driving distribution and abundance.

Organization of Communities and Population Growth

• Limits to Exponential Growth: In real-world environments, populations cannot grow indefinitely. Growth is constrained by several factors:

  • Abiotic Conditions: Non-living environmental factors like temperature and salinity.

  • Limiting Resources: Essential requirements for life that are in short supply.

  • Interactions: The relationships between organisms which can be intra-specific (within the same species) or inter-specific (between different species).

  • Direct vs. Indirect Interactions: Direct relationships involving two organisms versus complex interactions mediated through a third party.

• Population Growth Formula: The doubling time ($T_2$) of a population given a growth rate ($r$) is expressed by the formula:

$T_2 = \frac{\text{ln}(2)}{\text{ln}(1+r)}$

Species Interactions: Direct and Indirect

Direct interactions are categorized by their effect ($+$, $-$ or $0$) on the two organisms involved:

• Competition ($-/-$): Both organisms are negatively impacted as they vie for limited resources.

  • Limiting Resources for Plants: Includes nutrients, light, and space (especially for sessile organisms).

  • Limiting Resources for Animals: Includes food, space, and potentially water (in intertidal zones).

• Consumption ($+/-$): One organism benefits while the other is harmed or consumed. This category includes:

  • Predation: The entire consumption of an organism.

  • Herbivory/Grazing/Browsing: The partial or total consumption of primary producers.

  • Parasitism: One organism lives on or in a host, causing harm but not necessarily immediate death.

• Amensalism ($0/-$): One organism is negatively affected while the other remains unaffected ($0$).

  • Chemical Impacts: Production of waste products such as Hydrogen Sulfide ($H_2S$ or SH2).

  • Physical Impacts: Biological disturbances including trampling or bioturbation.

• Mutualism ($+/+$): Both species derive a benefit from the interaction.

  • Anemone-fish Relation: Amphiprion (fish) provides cleaning services, nutrients, and protection; the Sea anemone (Radianthus) provides physical protection.

  • Hermatypic Corals: Anthozoa (coral) provides stability, space, protection, and nutrients; Symbiodinium (Zooxanthella/dinoflagellate) provides organic carbon and food via photosynthesis.

• Commensalism ($+/0$): One organism benefits while the other is unaffected.

  • Examples: Habitat-formation, protection, and epiphytism (individuals growing on others, sometimes referred to as 'structural parasites').

• Keystone Predation: Identified through Robert Paine’s classic sea star removal experiment (1966). This occurs when a predator prefers to eat a species that is a strong competitor, thereby maintaining biodiversity by preventing the competitor from monopolizing resources.

• Indirect Interactions: These occur when Species 1 indirectly affects Species 3 through its interaction with Species 2. Theoretically, there are an infinite number and type of indirect interactions within an ecosystem.

Marine Life-Styles and Environments

• Life-Style (Functional Groups):

  • Plankton: Organisms that drift with the currents.

  • Nekton: Organisms capable of swimming against currents.

  • Benthos: Organisms living on or in the seafloor.

  • Mobility: Organisms are classified as either mobile (moving freely) or sessile (attached to a substrate).

• Environments (Habitats):

  • Pelagic: The water column environment.

  • Benthic: The seafloor environment.

  • Benthic-Pelagic Coupling: The interaction and exchange of materials/energy between the seafloor and the water column.

  • Subdivisions: Habitats are further classified based on depth, distance from shore, geomorphology, and wave exposure.

Flow of Energy and Materials: Trophic Structure

• Trophic Levels: Energy flows through different levels, and approximately $90\%$ of energy is lost as heat or waste at each successive level.

• Food Chains vs. Food Webs:

  • Food Chain: A simple, linear pathway of energy flow (e.g., short chains in Antarctica).

  • Food Web: A complex network of interconnected food chains (e.g., the complex North Sea web vs. the simpler Antarctic web). Descriptions of webs include the number of links and the size-structure of organisms.

• Primary Productivity: The process by which plants (primary producers) fix inorganic carbon to fuel the rest of the trophic structure.

  • Measurement Methods:

    1. Light-Dark O2 Container Experiments: Measuring changes in oxygen levels to determine metabolic rates.

    2. Fluorescence: Used as an instant proxy for photosynthesis.

Nutrient Cycling

• Nutrient Cycling (CNP): The movement of Carbon ($C$), Nitrogen ($N$), and Phosphate ($P$) through the ecosystem.

• Mechanisms:

  • Pools: Amounts of nutrients stored in various parts of the ecosystem.

  • Fluxes: The rate at which nutrients move between different pools.

• Global Significance: Nutrient cycling is linked to primary productivity and global ecosystem health.