Chapter 27: Species interactions and Community Ecology Flashcards
mutualism
- describes close interactions between organisms that benefit both participants
- common example: tick birds, the oxpeckers that eat ticks (parasites) they find on their hosts, large mammals such as giraffes
parasitism
- describes close interactions between organisms In which one organism benefits at the cost of another
oxpecker and tick birds example
- Paul Weeks, a zoologist @ Cambridge;
- expected that if hosts, in his case cattle were well served by oxpeckers, the incidence of ticks would be higher on cattle w/o oxpeckers
- he found that exposure to oxpeckers did not coincide with lower tick infestations in cattle
- wounds on cattle exposed to these birds took longer to heal than those on cattle that weren’t exposed
= raised possibility that oxpeckers feed at wounds where their actions would give them access to blood, and would result in slower healing
- oxpecker could obtain insects at wounds
- data don’t support the suggestion that the hosts benefit from the interaction with oxpeckers
*oxpeckers don’t reduce tick infestations and even eat the hosts blood
- situation is not mutualistic because there is little if any benefit to the host
cleaner fish example
- remove parasites from the bodies and gills of other fish
- on coral reefs, cleaner stations are sites where fish find the cleaner fish and benefit from their feeding activity
- interact btwn cleaner fish and their hosts = mutualistic
- both appear to benefit from cleaning behaviour
ecological community
- an assemblage of species living in the same place, the presence or absence of certain species may alter the effects of such interactions in almost unimaginably complex ways
sympatric
- organisms interconnected by the flow of energy and wastes that are by-products of energy production and use
although sometimes neutral, interactions among species
- typically benefit or harm the organism involved
many relationships we witness today are the products of long-term evolutionary modification
interactions amog spcecies occur at what level? interactions among individuals?
- interactions among species occur at the individual level, and interactions among individuals are constantly changing, as are selection pressures in ecosystems
New adaptations that evolve in one species
exert selection pressure on another
- which then evolves adaptations that exert selection pressure on the first
co-evolution
occurs when genetically based, reciprocal adaptations occurs in two or more interacting species
- many good examples of co-evolution are provided by interactions amongst plants and their animal pollinators
how do ecologists describe co-evolutionary positions
- describe co-evolutionary positions between some predators and their prey as a race in which each species evolves adaptations that temporarily allow it to outpace another
when antelope population suffer predation by cheetahs
natural selection fosters the evolution of faster antelopes
- faster cheetahs may be result of this situation, and if their offspring are also fast then antelopes will also become even more fleet of foot
flower structures of many different flower species
monkey-flower species, have evolved characteristics that allow them to be visited by specific pollinators, such as either bees or hummingbirds
population interactions and their effects
Predation: +/- predators gain nutrients and energy; prey are killed or injured
Parasitism: +/- parasites gain nutrients and energy, hosts are injured or killed
Herbivory: +/- Herbivores gain nutrients and energy, plants are killed or injured
Competition: -/- both competing populations lose access to some resources
Commensalism: +/0 One population benefits; the other population is unaffected
Mutualism: +/+ Both populations benefit
How does Symbiosis occur
when one species has a physically and functionally close ecological association with other
- biologists define three types of these interactions
COMMENALISM
MUTUALISM
PARASITISM
Commenalism
one species benefits from and the other is unaffected by the interaction
- appears to be rare in nature because few species are unaffected by interactions with another
Mutualism
both partners benefit
- appears to be common among animal partners as well as plant and animal interactions, including xo-evolved relationships between flowering plants and animals pollinators and animal seed disperses
- animals that feed on a plant’s nectar or pollen carry the plant’s pollen from one flower to another
- animals that eat fruits disperse the seeds and plants them in piles of nutrient-rich feces
what do mutualistic relationships not require
active cooperation, as each species exploits the other for its own benefit
- some common association between bacteria and plants are also mutualistic
- association w/ Rhizobium and leguminous plants such as peas, beans, and clover is very important for introducing an essential nutrient into terrestrial ecosystems
bull horn acacia tree mutualism example
- relationship between the bull horns Acacia tree of Central America and small ants
- each acacia is inhabited by an ant colony that lives in hollows in the tree’s swollen thorns
- ants swarm out of the thorns to sting, and sometimes kill, herbivores and competitors, and occupied trees grow faster and produce more seeds than unoccupied trees
IN RETURN
- plants produce sugar rich nectar consumed by adult ants and protein rich structures that the ants feed to their larvae
the bull horn acacia tree mutualism example is described as being
OBLIGATORY
- at least for the ants ***
- the ants can’t subsist on any other food sources
- where one species depends entirely on another, the extinction of one must lead to change or the extinction of both, an important aspect of ecosystem functioning that informs our understanding of the myriad risks of human-driven species extinction
Honeyguide birds
- use a special guiding display to lead humans to beehives
- individuals in a Kenyan tribe, the honey-gathering Borans call honeyguides with a special whistle
- Boran honey gatheres that follow greater honeyguides are much more efficient at finding beehives than those working alone
- when the honey gatherer goes to the hive and raids it to obtain honey, greater honeyguides help themselves to bee larvae, leftover honey and wax
prokaryotes that inhabit the digestive tracts of animals
significantly expand the capacity for extracting nutrients and other important factors from ingested food, including by humans
parasitism
- one species, the parasite, uses another the host in a way that harms the host
is the oxpecker sceario mutualism or parsitism
MUTUALISTIC:
- if the oxpecker benefit from eating ectoparasites taken from their hosts, and if the hosts benefit by incurring fewer ectoparasites , then the relationship is mutualistic
PARASITISM:
- but if the oxpeckers benefit at the hosts’ expense, then the relationship is parasitic