Basics of Ecology and Evolution II: Ecological Interactions Lecture Objectives: 1. Learn basic concepts of Ecology 2. Learn 5 major categories of interactions 3. Be introduced to ways humans alter interactions
Environment can be divided into biotic and abiotic factors
Biotic - Living portions of the environment
Predation, parasitism, competition, etc.
Abiotic - Nonliving factors
Rain, soil type, temperature, etc.
All organism have a range of requirements that determines where they can live The biotic and abiotic factors of any particular place determine where they do live
Tolerance Limits – refer to minimum and maximum levels beyond which a particular species cannot survive or reproduce.
Niche – Total set of environmental factors that determines a species ’ distribution.
The House Sparrow was introduced into Brooklyn, New York, in 1851. House Sparrow Native to Europe
Interactions among organisms What are some biotic factors that contribute to this differential survival and reproduction? 1. Predation 2. Competition 3. Parasitism 4. Commensalism 5. Mutualism
1. Predation (positive for consumer, negative for prey) One animal consumes another organism Interactions among organisms
Types of predators Active predators: chase & overpower prey http://www.youtube.com/watch?v=iarsmqA3dck
Antlion Sit-and-wait predators: motionless until prey close enough to strike
Cryptic Coloration: blend in with environment Many prey items have traits that reduce predation http://www.youtube.com/watch?v=SCgtYWUybIE
Warning Coloration: conspicuous to convey threat Many prey items have traits that reduce predation
Batesian Mimicry: defenseless species (mimic) is protected from predation by its resemblance to a species that is dangerous fly (bee mimic) bumble bee Many prey items have traits that reduce predation
Mullerian Mimicry: 2 or more distasteful or harmful organisms resemble each other Many prey items have traits that reduce predation
Interactions among organisms 1. Predation
Prey is harmed (-) by being eaten
Predator benefits (+) from food
Predation is a (+ / - ) relationship
Competition: organisms compete for the same limited resource Ex. light, food, mates, habitat, etc. 2. Competition Competition is a (- / - ) relationship Note: book makes it more complicated by calling it a ( ±/±) relationship Interactions among organisms
Intraspecific competition — Members of same species competing for resources
Members of different species competing for resources
May lead to competitive exclusion
Photos: Alex Wild
3. Parasitism 1 organism ( parasite ) living in or on another organism ( host ), from which it derives nourishment Ex. Tapeworm Interactions among organisms Parasitism is a (+ / - ) relationship
3. Parasitism (+,-)
Ectoparasites —Live on host ’s surface
(e.g., Fleas, lice, some molds)
Endoparasites —Live inside host.
(e.g., worms, protozoa, bacteria, fungi)
Ex. Heartworm 3. Parasitism (+,-)
Malaria carrying mosquito
Vectors : animals that carry parasite from one host to another
Examples: Malaria, Lyme Disease, West Nile Virus, Bubonic Plague
Nest Parasitism Common Yellow-throat Adult cowbirds don ’t build nests Cowbird
Interactions among organisms 4. Commensalism — One organism benefits, while the other is unaffected. Commensalism is a ( + / 0 ) relationship Remora and shark
Interactions among organisms 5. Mutualism - Both species benefit (+/+). Acacia and ants *Tree provides nectar that the ants eat *Ants defends tree against grazers
Summary of 5 major Interactions Predation Competition Parasitism Commensalism Mutualism Ind. 1 Ind. 2 Explanation Example
Food webs: All species in a community are interconnected to varying degrees.
An estimate of interactions among species between only 2 trophic levels (10,000 plants and 100 herbivores) in Hawaii Sheppard et al. 2004 Mol. Ecol.
From Cohen et al. 2003 PNAS
Producers convert sunlight to biomass 90% of useful energy lost as heat from one trophic level to the next Some energy always lost whenever it is converted between forms (2nd law…)
Keystone species : a species that plays an essential role in community stability. Indicator Species : a species that provides information about the quality of an area. (could be rare or a habitat specialist) Umbrella species : a species that can be used as a surrogate for the heath/status of the entire community. (tend to need a lot of area)
Do all species matter? Is there redundancy in communities? On average, there are only 2 degrees of separation between any two species in a food web. Paul Ehrlich made an analogy between species in communities and rivets on the wing of an airplane. Removing a few rivets from an airplane is undoubtedly safe. How many are you willing to remove?
Percentage of threatened or endangered species in the U.S. imperiled by: Why are species declining? Disease - 3% Overexploitation - 17% Pollution - 24% Invasive species - 49% Habitat degradation and loss - 85% Dave Wilcove et al. 1998 BioScience
Photo: Darren Irwin
How have people changed these interactions? 1) Introduced species 2) Habitat destruction or alteration Introduction of novel predators and parasites can devastate natural communities. 3) Hunting / exploitation
Over 2,000 species of birds have gone extinct on islands as a result of habitat loss and the introduction of predators and parasites.
Hawaii: Habitat loss, malaria, rats and mongoose
Practice exam question: In the trophic pyramid, the relationship between an herbivore (primary consumer) and a producer is best described as which type of ecological interaction? a) Commensalism b) Mutalism c) Interspecific competition d) Predator-prey e) Host-parasite
By the end of this lecture you should be able to:
Define biotic and abiotic environmental factors and explain how each influence a species ’ niche.
List the 5 main types of species interactions and tell who benefits from each type of interaction (e.g., +/+, +/-, etc.)
Recognize examples of the types of species interactions.
Understand food webs and degrees of separation within them
Explain how humans influence these interactions.
List some strategies used by prey species to avoid being eaten.