Species interactions
Species interactions
A predator is an organism that feeds directly upon another living organism, whether or not it kills the prey in doing so
Prey most successfully on slowest, weakest, least fit members of target population
Reduce competition and population size
Predation exerts a selective force
Co-evolution
Coevolution – “Arms Race”
Natural selection promotes traits that help prey escape or deter predation
It also promotes traits that make predators more successful at capturing or eating prey
Types of predation
Predator-Prey
Predator-prey in the microscopic world
When the prey (Paramecium) are used up in the test tube, the predator (Didinium) also dies
Population dynamics
Herbivores can have dramatic effects on plant populations.
Major basis of bio-control
Prickly pear introduced into Australia in 1839
By 1925 was in 240,000 km2
Released moth from South America in 1925
Prey adaptation to avoid predation
Prey and predators are not evolutionarily passive
There exist a large suite of adaptation of prey that decreases the likelihood of being consumed
Such variety, and commoness of these traits is evidence of the strong selective pressure of predation on evolution
Prey Defenses
Chemical
Camouflage/crypsis
Catalepsis
Warning coloration
Mimicry
Displays
Morphology
Masting
Chemical
Chemical defenses
Can be used in attack, or following consumption
Cane Toad and native animals
Naïve predators
Camouflage
Crypsis and catalepsis
Coloration and markings to blend in to the surroundings
Development of a frozen posture
Warning coloration
Aposematic coloration
Mimicry
Batesian mimicry - Harmless species evolve characteristics that mimic unpalatable or poisonous species
Mimicry - Batesian
Monarch-Viceroy
Mimicry of a unpalatable species (MODEL) by a palatable one (MIMIC)
Mimic success is dependent upon mimic:model abundance
High mimic abundance can harm model
Mimicry
Mullerian Mimicry - Two unpalatable species evolve to look alike
Mimicry - Mullerian
Evolutionary convergence of unpalatable (or dangerous) species to look and act the same
Yellow-black striping in wasps and bees
There are often Batesian mimics of Mullerian mimicry complexes!
Many harmless yellow/black flies
Intimidation displays
Many organisms can “increase” size in response to danger
Give appearance of being larger – and thus bigger threat
Can also just startle predator – deters ambush predators
Masting
Synchronous production of many progeny by all individuals in a population
Saturates predators
High juvenile mortality, but less than if only a few offspring produced
Morphological
Physical deterrent to predator
Can be induced
Phenotypic plasticity
Daphnia
Spikeless vs Spiked forms
Chemically induced
Behavior to avoid defense
Predator Responses
Predator adaptations include stealth, camouflage, and ways to avoid chemical repellents
Symbiosis
Symbiosis - Intimate living together of members of two or more species
Commensalism - One member benefits while other is neither benefited nor harmed
Mutualism - Both members benefit
Parasitism - One member benefits at the expense of other
Commensalism
Commensalism
Difficult to distinguish
Can cross over into mutualism or parasitism or have characters of both
Mutualism
Both species benefit
Mutualisms can be obligate or facultative
Some are more intimate relationships than others
Yucca and yucca moth
An obligatory mutualism
Each species of yucca is pollinated by only one species of moth
Moth larvae can grow only in that one species of yucca
Rhizobium
Acacia and ants
Ants get nectar and a place to live
Ants provide protection and reduction in competition
Cleaner fish
Seed dispersal
Mycorrhizae
Association between plant and fungus
Can strongly influence growth and survival
Parasitism
Parasites drain nutrients from their hosts and live on or in their bodies
Defined by size and location on host
Ectoparasites vs. endoparasites
Microparasites vs. macroparasites
Natural selection favors parasites that do not kill their host too quickly
Have complex life cycles
Parasitoid