Fish Ecology Flashcards
Trophic ecology
Fish don’t have hands, constraint on what they can eat, gape limited predation, profound effect on structure of fish communities.
Exceptions like cookie cutter shark.
Trophic level increases as a function of body size
Consistent relationship between the size of a predator and its prey, Predator prey mass ratio.
On average fish consumers a 100-10,000 times larger than their prey.
Blue fin tuna grows over 6 orders of magnitude over its life, implies that it goes through at least 3 whole trophic levels through its lifespan.
Doesn’t make sense to assign a trophic level so we use body size in marine food webs.
Flow of energy
10%, trophic transfer efficiency
Biomass and body size are related by PPMR/transfer efficiency, able to predict what the biomass should be of a species.
PP are small cells
Primary consumers need to be able to use short lived and dispersed carbon stores.
Transfer efficiency at low trophic levels may be higher than 10%
V small offspring feed at low trophic levels where C is concentrated, use higher efficiency.
Movement
Inertial drag increases with speed, and fish can’t change body shape to counteract it.
Slow speeds are energetically efficient powered by small amount of muscle.
White muscle can be very costly, after anaerobic swimming, must recover oxygen debt and excrete carbon dioxide.
Swimming speeds can be too high to be sustained by red muscle, oxygen after white = post excerecise oxygen excess.
While trying to regain, less scope for other activities for digestion or evasion.
Reynold’s number
Big fish swimming relatively fast has a high R, drag is largely inertial
Small fish fights against viscous drag
Energetic cost of swimming a given distance is much greater at small body sizes.
Larvae are small, energetically costly laminar flow, as they grow energetic cost decreases exponentially, as you grow fewer bigger than you, major incentive to grow quickly
Diet and movement in life history
Small larvae for efficient tissue production but:
Lots of predators.
High mass specific metabolic rate and oxygen demand
High energetic cost of swimming
Problems reduced as body size increases, maximise growth rate and live somewhere with few predators.
Energetic cost of swimming at surface is less than it would be for a fish swimming against inertial drag.
Larvae benefit from surface, shallows and time period where food is most available.
Habitat needs change through life stages.
Most fish will show ontogenetic migration between feeding and spawning areas.
Migration
Persistent and straightened out movement effected by the animal’s own locomotry exertions.
Migration behaviour depends on some temporary inhibition of station keeping responses but promotes their eventual recurrence.
Types of migration
Adopted, behaviour from experience to young individuals
Differential, change in behaviour related to demographic attribute.
Homing, directed movement to a previous location.
Irruptive, coincident expansion in abundance and spatial distribution.
Ontogenetic, movement randomly at specific life stages or gradually over the lifetime of individuals.
Partial, coexistence of two or more life cycles within a population
Philopatry, multi-generational return of a population to a breeding site that leads to reproductive isolation.
Connectivity
When an animal moves or migrates, links different places.
Connectivity can lead to food subsidy, where animals move nutrients from one area to another.
Connectivity is genetic, populations can be linked through movements of individuals between populations.
Connectivity tends to increase resilience to local disturbance, but is problematic for virus spread.
