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