behavioural ecology of fishes

BEHAVIORAL ECOLOGY

OF FISHES

outline Introduction

Interactions and behaviours Feeding behaviour Predation Parasitism Mutualism Commensalism Neutralism Migration Communication Camouflaging Mating and spawning behaviour

Introduction

Behavioural ecology is the study of the evolutionary basis for animal behaviour due to ecological pressures.

It also includes the study of Interactions like,

Feeding behaviour, Predation , Parasitism, Mutualism, Commensalim,Neutralism,Migration, Communication,Camouflaging,

Mating and spawning behaviour

Feeding Behavior Feeding behaviour is a complex behaviour that is

closely associated with food intake. Fish have a wide variety of feeding habits and

feeding patterns making them good experimental models for the study of the regulation of feeding behaviour.

Feeding behaviour is regulated by a number of environmental factors and also by complex homeostatic mechanisms that involve central and peripheral hormonal factors as well as metabolites.

Example - Sunfish, provide predator with prey of different sizes and different densities, fish respond by foraging optimally (taking the most energetically rich prey under the appropriate conditions)

Optimal ForagingIt is a model that helps predict how an

animal behaves when it's searching for food. Although obtaining food provides the animal with energy, searching for and capturing the food require both energy and time.

• All else being equal, take the largest prey • Don’t choose prey that takes more energy than it provides •it will Be in a habitat that provides the type of food which is looking for

Finding Food

• Visual detection – Diurnal feeders – Means being in the open in bright light • Olfaction – Common in bottom dwelling species

Predation Most fish species are

simultaneously predator and prey

Very few strict herbivores, detritivores (and young usually are insectivores)

Better predator, more elusive prey

Porcupine fishes

Predator Strong beak/teeth

Prey Spiny covering,

toxins

Barracudas

Predator Sharp teeth

Prey Sleek bodies

Minnows

Predator Pharyngeal teeth

Prey Fear scents

Herrings

Predator Fine gill rackers

Prey Schooling behavior

Predators control prey

Typical situation E.g., largemouth bass control bluegill -

regulate population abundance, size structure

Prey control predators

A typical situation E.g., bluegill in Lake Winona eat bowfin

eggs, young ones, to control the population density.

Prey switching behaviorOptimal foraging theory

Alternate prey present- switch as needed to maximize energy intake vs. energy expenditure

E.g., bluegill - zooplankton, benthos

Intra specific Predation Competition among members of the

same species is known as intraspecific competition,

while competition between individuals of different species is known as interspecific competition.

Cannibalism - bluegill males may consume eggs, young of nest neighbors

Competition competition can be defined as an

interaction between organisms or species, in which the fitness of one is lowered by the presence of another.

 Limited supply of at least one resource (such as food, water, and territory) used by both usually facilitates this type of interaction,

although the competition may also exist over other 'amenities', such as females for reproduction (in case of male organisms of the same species).

Food, habitat, mates,etc..

Competition Resource

partitioning via some approach

Behavioral, morphological

E.g., feed in different habitats, or at different times

Character displacement

Alewife invasion(herring) of Lake Michigan shifted ciscoes sp.from planktonic to benthic feeding (and reduced number of gill racers)

Competition Differential exploitation

One species more efficient than another at using a resource

Brown bullhead and pumpkinseed both prefer benthos, but bullhead more efficient

Forces pumpkinseed to switch to zooplankton

Competition

Predation can both decrease and increase competition among fishes

Decrease by reducing numbers so that resources no longer are limiting

Increase by forcing fish together into restricted habitats

Competition

Habitat imprinting may be an evolved behavior to minimize interactions, allowing greater coexistence among species or subspecies

Intraspecific Competition

Size segregation - large adults in different habitats than small adults, juveniles

Large adults occupy habitats with highest benthos densities

Symbiosis

Living together Mutualism, commensalism, parasitism

Symbiosis Sometimes it is used only for cases

where both organisms benefit; sometimes it is used more generally to describe all varieties of relatively tight relationships, i.e. even parasitism, but not predation. 

Mutualism - both parties benefit Commensalism - one benefits, the

other receives no benefit or harm Parasitism - one benefits, the other is

harmed

Mutualism

Mutualism is an interaction between two or more species, where species derive a mutual benefit, for example an increased carrying capacity.

Minnows shoaling together in streams, lakes of eastern North America

Mutualism

Cleaning behavior Cleaner wrasses

Commensalism

Commensalism benefits one organism and the other organism is neither benefited nor harmed. It occurs when one organism takes benefits by interacting with another organism by which the host organism is not affected.

A good example is a remora living with a shark. Remoras eat leftover food from the shark.

The shark is not affected in the process, as remoras eat only leftover food of the shark, which does not deplete the shark's resources.

Neutralism

Neutralism describes the relationship between two species that interact but do not affect each other. It describes interactions where the health of one species has absolutely no effect whatsoever on that of the other.

Amensalism

Amensalism is an interaction where an organism inflicts harm to another organism without any costs or benefits received by the other.

Parasitism

Pearl fishes - leave in sea cucumbers Enter body cavity through anus - feed on

gonads One host per lifetime - stays alive

Parasitism

Bitterling - lay eggs into freshwater mussels

Embryos develop from nutrients within gill cavities

Parasites & Pathogens

Major outbreaks and fish die-offs are regular occurrences

Parasites and pathogens most “evolved” if they do not kill their host

Parasite Generalities

Pelagic fishes tend to have fewer parasites than benthic, near shore species (snails, copepods)

Bigger fish have more parasites (numbers and types)

Fish Migration

• Reasons for migration – Food gathering – Temperature adjustment – Breeding

Timing of migrations

– Annual – Daily – generational

Classification of Fish Migration

Diadromous – Travel between sea & fresh water

– Anadromous – most of life at sea, breed in fresh water – Catadromous – most of life in fresh water, breed at sea – Amphidromous – migrate between water types at some stage other than breeding

• Potamodromous – Migrate within a fresh water system

Ocenodromous – Migrate to different regions of the ocean

Reasons for Migrations

• Take advantage of different habitats – Feeding – Protection • Avoid adverse conditions • Meet requirements for reproduction

Shoaling and its characteristics Shoal - any group of fishes that

remains together for social reasons School - a polarized, synchronized

shoal (has coordinated, directed movements)

Requires great deal of coordination among individuals in the school

Vision is primary sensory cue for coordinating movement

individual movement is coordinated with movement of some other visually distinctive object - e.g. a spot or a stripe

Benefits of Shoaling

• Gives a predator many moving targets – Confuses predators

– Increases food finding ability • Keeps potential mates in close proximity

•It is the mechanism to escape from predation.

Disrupt the outline of the fish – Make them less visible – Often associated with beds of plants

Also known as “protective resemblance” or “aggressive resemblance”...depends on state of animal.

• Being dark on top, light on bottom – Look like substrate from above – Look like water surface from below

Eye Spots

• Usually at base of caudal fin – Usually used to confuse predators • Common in some fry – Sometimes used for species recognition

Lateral Stripes

• Mid-lateral band usually • Best developed in schooling fish – Keep school oriented while confusing predators – Makes it hard to pick out individuals

Auditory Signals

• Most fish produce sounds • Uses for sound – Courtship singing – Territorial defense – Signaling shoal

Sound Production

• Stridulation – Rubbing hard surfaces together – Low frequency sounds • Vibration of swimbladder – Can give loud croaking • Incidental to other activities

Chemical Signals

• Pheromones released into the water – Reproductive cues – Recognition • Schreckstoff = fear scents – Predator avoidance – Produced in epidermal cells

Refrences

http://en.wikipedia.org/wiki/Behavioral_ecology

Behaviour of fishes-A N Shukla. http://en.wikipedia.org/wiki/

Biological_interaction#Neutralism

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