Marine Ecology: Predator-Prey Interactions

Ecological and Evolutionary Principles

• Ecology (ECOS) studies interactions between organisms and their environment, and how these influence distribution and abundance.
• Resources can be renewable or non-renewable.
• Ecological hierarchy includes individual, population, community, ecosystem, and biosphere.
• Nutrients can be old or new.

Interactions on the Scale of Individuals

• Ecological interactions can be classified as plus-minus-zero, based on whether species benefit, suffer, or are unaffected.
• Territoriality involves defending a home range.
• Predation involves predators searching for prey using chemical, mechanical, and visual stimuli.
• Mobile predators can adjust hunting behavior to optimize prey ingestion (optimal foraging theory).

Predator Avoidance

• Resistance to predators increases fitness due to natural selection.
• Marine organisms avoid predators through crypsis, deceit, and escape responses or by developing morphological features like spines or tentacles.
• Chemical defense mechanisms, like toxic compounds, acid secretion, and toxins, are often associated with conspicuous coloration.
• Mechanical and chemical defenses change with temperature, location, and oceanic basins.
• Microhabitats can affect vulnerability.

Interactions on the Scale of Individuals: Other Interactions

• Commensalism benefits one species without affecting the other. Benefits are food, substrate or space. (e.g., tube worms, crab larvae or fish larvae)
• Mutualism benefits both participants. It can reduce predation risks or provide food.
• Parasitism occurs when one species (parasite) lives at the expense of another (host), without necessarily killing it. Parasites often have complex life cycles involving multiple hosts.

Complex Life Cycle of Marine Parasites

• Describes the life cycle of a marine parasite, including stages like eggs, miracidium, sporocyst, redia, cercaria, and encysted metacercaria, along with different hosts involved in the life cycle.

The Population Level

• A population is a group of individuals in the same environment, relatively unconnected to other species populations.
• Characteristics of populations can be size, density, or biomass.
• Population change is driven by survival, birth, death, immigration, and emigration.
• Limiting resources can affect population growth.
• Examples of factors are ocean acidification or generation time/year class/growth rings.

Interspecific Competition

• Populations of different species competing for resources can have effects on the populations.
• Observed interspecific competition effects can be studied using Gammarus experiments across different time-scales.

Spatial Variation (distribution)

• Spatial distribution measures spacing among individuals within a given area.
• Populations may show density changes along sampling lines (vertical or horizontal).
• Patterns include random, uniform, and aggregated/patchy.
• Spatial variation in distribution is a reflection of dynamic environments.
• Spatial autocorrelation is the prediction of population density of one site from a neighboring site. Changes in environment, migration, or randomness can affect patterns.

The Ecosystem Level

• An ecosystem consists of interconnected communities in a geographical area.
• Ecosystems are mostly self-sufficient.
• Key factors in ecosystems include primary producers (plants), herbivores, and carnivores and materials escaping from the primary cycle, impacting biomass and productivity.
• Ecosystem studies investigate how materials and energy flow through food webs.

Processes in the Open Sea

• Critical factors affecting plankton abundance are the presence of different plankton types in different areas, and their abundance relative to each other.

Introduction: Seasonal Patterns of Plankton Abundance

• Seasonal changes in plankton abundance are observed in mid-latitudes. Plankton increase in spring and decline in summer, with some increase in the fall.
• Phytoplankton blooms peak during spring, followed by a zooplankton peak in the early summer.

Eutrophic and Oligotrophic Ecosystems

• Eutrophic and oligotrophic ecosystems have distinct seasonal patterns in plankton abundance. The factors affecting these patterns, like physical factors (mixing, ice), grazing, nutrient limitation, temperature, predation, and food limitations are different and can be measured through different periods in a year.

Water Column Parameters

• Light decreases exponentially with depth.
• Photosynthesis is offset by respiration below a certain depth (compensation depth).
• Winter water density is consistent through the water column, making phytoplankton mixing average in depths preventing photosynthesis from causing a population increase.
• Maximum depth and water column stability are critical factors influencing plankton populations.

Stability and Light

• Spring temperature increases, leading to warming surface water, stabilizing the water column.
• Nutrients move to deeper water, hindering phytoplankton blooms.
• Nutrient exchange between the bottom and water column and input from the spring freshet influence phytoplankton growth.
• Productivity, production, and assimilation number are key measurements to understand phytoplankton populations.

Light

• Light inhibition is often observed near the surface, and the intensity of light influences photosynthesis.
• Visible light spectrum is critical for photosynthesis, captured by a series of photosynthetic pigments.

Nutrients Required by Phytoplankton: Nitrogen

• Nitrogen is crucial for protein synthesis and absorbed as ammonium, nitrite, and nitrate.
• Nitrogen cycling involves new production and regenerated production, occurring between phytoplankton and the bottom in shallow water.
• Zooplankton excretion is another major source of recycling.
• Microbial transformation is deeply involved with nitrogen cycling.

Nutrients Required by Phytoplankton: Phosphorous

• Phosphorous occurs as inorganic phosphate in seawater and is a crucial energy source for enzymatic reactions. The ratio of nitrogen to phosphorous is generally 15:1 in the sea, controlled by uptake and decomposition based on pH.

Nutrients Required by Phytoplankton: Silicon

• Silicon is primarily for diatoms.

Nutrients Required by Phytoplankton: Trace Metals

• Trace metals play a vital role in oxidation processes and iron is a cofactor in oxygen evolution during photosynthesis.

Phytoplankton Succession

• Seasonal sequence of phytoplankton species is influenced by nutrient availability. Different species have differing nutrient needs, influencing their succession.

The Microbial Loop

• Heterotrophic and chemoautotrophic phytoplankton utilize molecules, and bacteria are major heterotrophic consumers in the water column. Protists consume water column bacteria, serving as a food source to zooplankton.

Rate of Nutrient Uptake

• Nutrient uptake increases with increasing nutrient concentration up to a plateau.
• Inshore plankton are adapted to high nutrient concentrations while open ocean plankton are more efficient at lower concentrations.
• Stable water columns, nutrient input, and resting stages of phytoplankton promote dense blooms, which involves phytoplankton and some cyanobacteria.

Zooplankton Grazing

• Zooplankton abundance often mirrors phytoplankton availability.
• Zooplankton grazing growth is dependent on phytoplankton growth, and grazing does not always control phytoplankton abundance.
• Feeding behavior varies based on phytoplankton cell size and concentration.
• Copepods have selective feeding and involves plucking rather than straining.

Biomenioskelion

• Different species of plants and animals, such as Phragmites australis, Trapa natans, and Ceratophyllum demersum, can grow in different locations in lakes. These locations can be determined based on the depth of the lake.

Data on Phytoplankton and Zooplankton

• Data and figures on variations in phytoplankton and zooplankton biovolumes and concentrations across several timescales and depths.
• Data on rates of primary primary production and chlorophyll in different ecosystems.
• Food webs and interactions between different species.

Explore ecological relationships in marine environments. Learn how species interact through predation, defense mechanisms, and habitat maintenance. Understand predator-prey dynamics and adaptations for survival in the ocean, including crypsis and morphological defenses.