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 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
in some cases, as in mutualistic relationships, a parasite’s survival can depend
upon exploitation of its host
many parasite-host interactions can be considered to be specialized
predator-prey relationships because one population of organisms feeds on another
- most of these parasites differ from predators, because they do not usually directly kill their prey; a dead host is not a continuing source of nourishment
blood feeding insects
represent less than 1% of all identified species of insects
- warm blooded ones ingest more than cold blooded ones
parasitoids
- fall somewhere between true parasitism and predation
- LIVE ON EXTERIOR OF HOST
- a female parasitoid lays her eggs in a larva or pupa of another insect species, and her young consume the tissue of the living host
endoparasites
- tapeworms, flukes, and roundworms live WITHIN a host
- many endoparasites acquire their hosts passively when a host accidentally ingests the parasites’ eggs or larvae
- endoparasites generally complete their life cycle in one or two host individuals
ectoparasites
- leeches, aphids, and mosquitoes
- feed on the EXTERIOR of the host, most animal ectoparasites have elaborate sensory and behavioural mechanisms allowing them to locate specific hosts; they feed on numerous host individuals during their lifetime
plants such as mistletoes live as
ectoparasites
- on trunks and branches of trees; their roots penetrate the host’s xylem and extract water and nutrients
birds laying their eggs in the nests of conspecifics (members of the same species)
- leaving the host species to invest energy and resources in raising young that are
1) not their own
2) don’t contribute towards increasing their species’ population
i.e. brown headed cowbirds through blood parasitism have played a role in contributing to the precipitous population decline of Kirtland’s Warbler populations
photosynthesis
trapping light from the Sun Rays and converting it to chemical energy
- some animals harvest chloroplasts for example, solar sea slugs harvest chloroplasts for them to emulate green plants
- some plants (pitcher plants) use it to obtain energy and nitrogen from animal excretory products
Nepenthes Lowii VS Nepenthes hemsleyana
provide pit toilets for tree shrews
- nectaries around the pitcher attract the shrews and provide them with a snack as they deposit feces and urine in the pitcher
Nepenthes Hemsleyana
- pitchers are modified to accommodate roosting bats
- which urinate and defecate into the pitcher
IN BOTH CASES
- isotopic analysis reveal that nitrogen from the tree shrews and bats is used by the plants
herbivores adaptations
- adapted to locate and process their food plants
- insects use chemical sensors on their legs and mouth parts to identify edible plants and sharp mandibles or sucking mouthparts to consume plant tissues or sap
Herbivores mammals
- specialized teeth to harvest and grind tough vegetation, herbivores such as farmer ants, ruminants and termites may co-opt other species to gain access to nutrients locked up in plant materials
optimal foraging theory
- predicts that an animal diet is a compromise between the costs and benefits associated with diff types of food
- assuming that animals try to maximize their energy intake at any meal, their diets should be determined by the ratio of cost to benefits; the cost of obtaining food versus the benefits of consuming it
what are the costs and benefits in an animals diet
- Costs are the time and energy it takes to pursue, capture, consume, and digest a particular kind of food
- benefits are the energy provided by the food
- cougar will invest more time and energy hunting and attacking a mountain goat than a jackrabbit but the payoff for the cat is a bigger meal
important element in food choice
relative abundance of prey
= encounter rate
- influenced by population density of prey and can influence a predators diet
i.e. when rabbits are more abundant they are a more economical meal for scarer prey for cougars
food abundance affects food choice
- when prey are scarce, animals often take what they can get, settling for food with a higher cost-to-benefit ratio
- when food is abundant, they may specialize, selecting types that provide the largest energetic return
i.e. Bluegill sunfishes eat Daphnia ssp. and other small crustaceans
- when crustacean density is high, these fishes take mostly large Daphnia, which provide a higher energetic return than small ones
- when prey density is low, bluegills eat Daphnia of all sizes
What do rattlesnakes use to detect warm blooded prey
face sensors
- the snakes deliver venom through fangs by open-mouthed strikes on prey
- after striking, the snakes wait for the venom to take effect and then use chemical sensors on the roofs of their mouths to follow the scent trail left by the dying prey
what is venom
- produced in the snakes’ salivary glands
- typically a bunch of proteins, including neurotoxins that paralyze prey ad protease enzymes that begin to digest it
- the specific components vary among venomous species
- elastic ligaments connect the bones of the snake jaws to one another and the mandibles to the skull allow snakes to open their mouths very wide to swallow prey larger than their heads
snails and insulin
- two species of cone snails use insulin to immobilize fish, facilitating the challenge of catching them
this causes hypoglycaemic shock and immobilizing the prey
how do plants prevent themselves from being eaten
- spines
- thorns
- and irritating hairs to protect themselves from herbivores
plant tissues often contain poisonous chemicals that deter herbivores from feeding
(example)
milkweed plants exude a milky irritating sap that contains poisons that affect the heart
- even small amounts of cardiac glycosides are toxic to the heart muscles of some vertebrates
- other plants have compound that mimix the structure of insect hormones, disrupting the development of insects that eat them
- some plants increase the production of toxic compounds in response to herbivore feeding
what do plants produce that are dangerous and even deadly
chemicals
- dangerous to humans to some other plants
size and defence
size can be a defence
- being too small to be considered food
- being so big that few predators can succeed in attacking and killing the prey
- relative size of predator and prey is central to this situation
first line of defence of animals
- avoiding detection
- not moving
- keeping a sharp lookout for the danger presented by approaching predators
- animals that live in groups benefit from the multitude of eyes and ears that can detect approaching danger, so the risk of predation influences group size and social interactions
camouflage
- another line of defence for animals
- camouflages so that a predator does not distinguish them from the bg.
- i.e. the stripes of a zebra make the animals conspicuous at close range, but at a distance, patterns break up the outline, rendering the animals almost invisible
- some caterpillars look like bird droppings whereas other insects look like thorns or sticks, because these aren’t usually eaten by insectivores
what do animals do when they’ve already been discovered and recognized
- take refuge in a shelter and getting out of a predators reach are alternatives
- African pancake tortoises are flat
- when threatened, they retreat into rocky crevices and puff themselves up with air, becoming so tightly wedged that predators cannot extract them
if cornered by a predators
- displays intended to startle or intimidate by making the prey appear large and/or ferocious
- may dissuade a predator or confuse It long enough to allow the potential victim to escape
- may animals use direct attacks in this case, with whatever weapons they have these are not a good primary defence because they usually involve getting very close to the predator, something prey usually avoid doing
other organisms use active defence
- in the form of spines or thorns
- porcupines release hairs in quills
- some organisms are armoured
chemical defence
- smelling or tasting bad
- skunks and bombardier beetles escalate this strategy by producing and spraying a noxious chemical
- some animals vomit and defecate on their attackers
- some produce dangerous toxins ad deliver them directly to their attackers
- these toxins may be synthesizes by the user or sequestered from other sources, often plants or other animals
i..e caterpillars of monarch butterflies are immune to the cardiac glycosides in the milkweed leaves they eat
- they extract, concentrate, and store these chemicals, king the caterpillars themselves poisonous to potential predators
aposematic displays
- many noxious or dangerous animals are aposematic
- they advertise their unpalatability with an appropriate display
- designed to teach predators to avoid the signaller, reducing the chances of harm to would-be predators and prey
- predates that attack a brightly coloured bee or wasp and are stung learn to associate the aposematic pattern with the sting
- predators quickly learn to avoid these animals (skins, yellow banded wasps, etc)
T/F: some predators will eat mainly dangerous prey
- T
- bee-eaters are birds that eat hymenopterans
- some individual African lions specialize in porcupines, and animals such as hedgehogs seem able to eat almost anything and show no ill effects
- some hedgehogs first lick toads and then their own spines, anointing them with toad venom
- hedgehog spines treated with toad venom are more irritating than untreated ones, enhancing their defensive impact
Mimicry
- since predators learn to recognize warning signals, many harmless animals defences are based on imitating dangerous or distasteful species
- mimicry occurs when one species evolves to resemble another
Batesian mimicry
- named for English naturalist Henry W. Bates, occurs when a palatable or harmless species resembles an unpalatable or poisonous one
- any predator that eats the poisonous model and suffers accordingly should subsequently avoid other organisms that resemble it
- however, the predator must survive the encounter
Mullein mimicry
- named for German zoologist involves two or more unpalatable species looking the same, presumably to reinforce lessons learned by a predator that attacks any species in the mimicry complex
what is needed for mimicry to work
- the predator must learn to recognize and then avoid the prey
- the more deadly the toxin, the less likely an individual predator is to learn by its experience = bc they’ll die
- predators learn by watching the discomfort of a conspecific that has eaten or attacked an aposematic prey
predators learning to circumvent defences
- many predators learn to deal with a diversity of prey species and a variety of defensive tactics
i.e. orb web spiders confronting a captive in a web adjust their behaviour according to the prey
- they treat moths differently from beetles, and they treat beetles in yet another way
- when threatened by a predator, headstand beetles raise their rear ends and spray a chemical from a gland at the tip of the abdomen
how does a mouse circumvent beetle mechniasms
grab the beetle
- avert its face to avoid the spray
- turns the beetle upside down so that the gland discharges into the ground
- eat the beetle from the head down
intraspecific competition
- when access to resources limits populations, individuals of the same species may compete among themselves for limiting resources such as food and shelter
- can reduce the size and population growth rate of one or more of the competing populations
interspecific competiton
- individuals of different specie using the same limiting resources experience
interference competition
- individuals of one species directly harms individuals of another species
- animals may fight for access to resources, as when lions chase smaller predators, such as hyenas, jackals, and vultures from their kills
- many plant species, including creosote bushes release toxic chemicals into the soil, preventing other plant species form growing nearby
exploitative competition
- 2+ populations use the same limiting resource, and the presence of one species reduces resource availability for others
Lotka and Volterra experiment
- independently proposed a model of interspecific competition, modfyipgin the logistic equation to describe the effects of competition between 2 species
- in their model, an increase in the size of one population reduces the population growth rate of the other
- in the 1930s, Russian biologist GF Gause tested the model experimentally, he grew cultures of two Paramecium species under constant laboratory conditions, regularly renewing food and removing wastes
- both species ate bacteria suspended in the culture medium
WHEN GROWN ALONE
- logistic growth
WHEN GROWN TOGETHER
- one species persisted at high density whereas the other one was almost eliminated
what did the results of Gause’s experiment lead him to define
the competitive exclusion principle
- populations of two or more species cannot coexist indefinitely if they rely on the same limiting resources and exploit them in the same way
- one species inevitably harvests resources more efficiently and produces more offspring than the other which negatively affects the other species
ecological niche
- concept to visualize resource use and the potential for interspecific competition in nature
- a species’ niche is defined by the resources it uses and the environmental conditions it requires over its lifetime
what does a niche include
- food
- shelter
- nutrients
- non-depletable abiotic characteristics of an ecosystem such as light intensity and temperature
an infinite variety of conditions and resources contributes to what
species’ niche
- in practice, ecologists usually identify the critical resources for which populations might compete
what are important resources for plants and what can they cause differences in?
- sunlight, soil moisture, and inorganic nutrients are important resources for plants so differences in leaf height, area, and root depth can affect their access to resources
fundamental niche
- the range of conditions and resources it (a species) could tolerate and use
realized niche
the range of conditions are resources that a species actually uses in nature
- these are smaller than fundamental niches because all tolerable conditions aren’t always present in.a habitat and some resources are used by other species
what does it mean if fundamental niches overlap between species
they MIGHT compete in nature
- not certain for ex. all terrestrial animals consume O2 but don’t compete for it bc its plentiful
resource partitioning
- when several sympatric species use different resources or the same resources in different ways
ex. although plants might compete for water + dissolved nutrients, they may avoid competition by partitioning these resources, collecting them from different depths in the soil
character displacement
- evidence when comparing species that are sometimes sympatric and sometimes allopatric
- evolutionary change that occurs when two similar species inhabit the same environment NS favours a divergence in characters
allopatric populations
morphologically similar
- use similar resources
sympatric populations
morphologically different
-use different resources
differences between sympatric species allow them to
coexist without competing
What did Allen Keast study
- honeyeaters (group of birds from Australia)
- in mainland=6 species
- on coast of Kangaroo Island=2 species
when species are sympatric
- each feeds in a wider range of situations than when 6 species live in the same area, reflecting the use of broader niches
- behavioural and morphological differences are evident when species are compared between the different situations
what does data on resource portioning and character displacement suggest (BUT NOT PROVE)
Interspecific competition is an important selective force in nature
- to demonstrate that interspecific competition limits natural populations, one must show that the presence of one population reduces the population size or density of its presumed competitor.
Joseph Connell (what did he examine)
- competition between 2 barnacle species
- he first observed the distributions of both species of barnacles in undisturbed habitats to establish a reference baseline
(1 species- shallow water on rocky coasts, where its periodically exposed to air Chthamalus Stellatus
1 species- typically lives in deeper water, where it is submerged) Balanus Balanoides
*w/o Balanus, Chthamalus colonize the area
- Balanus usually displace Chthamalus from rocks
- interference competition from Balanus appears to prevent Chthamalus from occupying areas
CONCLUSION: that there was competition between the two species but competition was asymmetrical because Chathamalus did not affect the distribution of Balanus, whereas Baluns had a substantial affect on Chthamalus.
K-selected species VS r-selected species
K-selected species:
- generally believe that competition has a profound effect on species distributions and resource use
r-selected species:
- agree that competition is not the major force governing community structure, pointing instead to predation or parasitism and physical disturbance
what can predators influence
the species richness and structure of communities by reducing the sizes of prey populations
- in BC, mussels are the strongest competitors for space often excluding other species from the community
- at some sites, predatory sea stars eat mussels, reducing their numbers and creating space for other species to grow
Robert Paine
- used removal experiments to evaluate the effects of predation of sea stars
keystone species
defined as species with a greater effect on community structure than their numbers might suggest
i.e. snowshoe hares
- prey for a range of predators
I.e. bats
- are also often keystone species because they eat insects and fruit and nectar
Jane Lubchenco
- studied herbivory in a periwinkle snail, believed to be a keystone species on rocky shores in Massachusetts
- features of plants and algae and the food presences of animals that can eat them can influence community structure, both increasing and decreasing species diversity
Frederic Clements
- of University of Minnesota championed an interactive view of communities
- he described communities as super organisms assemblages of species bound together by complex population interactions
= according to this view, each species in a community requires interactions with a set of ecologically different species, just as every cell in an organism requires services that other types of cells provide
what did Clements believe
- once a mature community was established, its species composition, the particular combination of species that occupy the site–was at equilibrium
- if a fire or some other environmental factor disturbed the community, It would return to its pre-disturbance state
Henry A. Gleason
- proposed an alternative, individualistic view of ecological communities
- he believed that population interactions do not always determine species composition
- a community instead is just an assemblage of species that are individually adapted to similar environmental conditions
HYPOTHESIS: communities do not achieve equilibrium, rather they constantly change in response to disturbance and environmental variation
Robert Whittaker
- suggested that ecologists could determine which hypothesis was correct by analyzing communities along environmental gradients, such as temperature or moisture
According to Clements interactive hypothesis, species that typically occupy the same communities should ___________
always occur together
- thus their distributions along the gradient would be clustered in discrete groups with sharp boundaries between them
According to Gleason’s individualistic hypothesis, _________
each species is distributed over the section of an environmental gradient to which it is adapted
- different species would have unique distributions and species composition would change continuously along the gradient
- in other words, communities would not be separated by sharp boundaries
What do most gradient analyses support
Gleason’s individualistic view of ecological communities
- environmental conditions vary continuously in space, and most plant distributions match these patterns
why do species occur together in assemblages
- because they are adapted to similar conditions, and the species compositions of the assemblages change gradually across environmental gradients
The individualistic view does not fully _______
explain all patterns observed in nature
- ecologists recognize certain assemblages of species as distinctive communities
ecotones
- borders between adjacent communities are often wide transition zones
- are generally rich with species because they include plants and animals from both neighbouring communities as well as some species that thrive only under transitional conditions
i.e. chemical differences between soils derived from rock and sandstone establish boundaries between communities of native cali. wildflowers and introduced grasses
biological communities are shaped by both
biotic and abiotic characteristics of ecosystems
- they vary in ecosystem structure, the number of species present, the roles those species play, the relative abundances of those species, and the ways in which these species interact
Growth forms of plants _________
- vary markedly in different environments based on the selection pressures of the ecosystem
different environments and the correlated characteristics of plants
- warm, moist environments= support abundant plant growth
- plants here compete for light, and create communities with complex and varying vegetation structure and multiple vertical layers
- tropical forestes include a canopy formed by the tallest trees, an understory of shorter trees and shrubs, and an herb layer under openings in the canopy
Physically harsh environments are occupied
only by plants able to survive such conditions
- leading to communities with plants characterized by low vegetation with relatively simple structure
species richness
- communities differ in species richness which is the number of specifies that live within them
i.e. harsh environment on a windy mountainside may support just a few species, while tropical forests that grow under milder physical conditions include many thousands of species
temperate deciduous forest
- southern Quebec, red oak trees and sugar maples might together account for nearly 85% of the trees
- in contrast, a tropical forest in Costa Rica may have more than 200 tree species, each making up a small percentage of the total
species evenness
- the relative abundance of species in an ecosystem is referred to as species evenness
how evenly individuals are distributed among the different species in a community
relationship between species diversity, evenness, and ecosystem functioning
positive
- ecosystem with higher species evenness are considered more diverse than ecosystems with lower species evenness
species diversity of species richness
- number of species
- simplest measure of diversity
i..e a forest with four tree species has higher species richness than one with two tree species
Shannon’s Index of Diversity
H’=-summation s I Pi ln Pi
- indices of diversity
S= total number of species in the community
Pi=proportion of S made up by species I
Higher the value of H’, the higher the diversity
Shannon evenness
EH= H’/lnS
Lower values of H’ and EH suggest
communities with few species (low H’ values) or uneven distribution (low EH values)
Higher values of H’ and EH suggest
suggest a rich array of species with evenly distributed individuals
alpha diversity
Beta diversity
alpha diversity: refer to species richness of one community as alpha diversity
(i..E number of species in 1 park)
beta diversity: refer to the species richness of one ecosystem as beta diversity
(i.E. number of species in the country which the park is located)
trophic levels
- visualize the trophic structure of a community as a hierarchy
- defined by the feeding relationships among its species
consumers
acquire energy and nutrients by eating other organisms or their remains
tertiary consumers
animals that eat secondary consumers make up the fourth trophic level
detritivores
scavengers
- form a separate and distinct trophic level
- extract energy from organic detritus produced at other trophic levels
decomposers
- type of detritivores
- small organisms. such as bacteria and fungi, that feed on dead or dying organic material
Will lose 10-15% of their energy due to respiration
why are simple straight line food chains rare in nature
- because most consumers feed on more than one type of food and because most organisms are eaten by more than one type of consumer
food webs
complex relationships
- sets of interconnected food chains with multiple links
biological hot spots
areas with many species
- coral reeds
- tropical forests
- icebergs
Robert MacArthur
- analyzed food webs to determine how the many links between trophic levels may contribute to a community’s stability
community stability def.
- stability of a community is defined as its ability to maintain species composition and relative abundances when environmental disturbances eliminate some species from the community
interspecific competition can cause what
local extinction of species or prevent new species from becoming established in a community, reducing its species richness
i.e. invasive species
what idea does research support
that communities are not in equilibrium and that species composition changes frequently over time
Joseph Connell and his colleagues conducted what study
long-term study of the effects of disturbance on coral reefs, they tracked the fate of the Heron Island Reef at the south end of Australia’s Great Barrier Reef, they found that coral communities in exposed areas were always in a flux
what are coral reefs
shallow tropical marine habitats that are among the most specific-rich communities on Earth
Cyclones and Reef (Joseph Connell)
- 5 major cyclones crossed the reef during the 30 year study period
- Coral communities in exposed areas of the reef were in a nearly continual state of flux
- in exposed pools, four of the five cyclones reduced the percentage of cover, often drastically
- on exposed crests, almost all corals were eliminated
- corals in sheltered areas suffered much less storm damage
- their coverage also declined steadily during the study as a natural consequence of the corals’ growth
they saw that the rate at which new colonies developed was almost always higher in sheltered than in exposed areas
what does the long-term study of coral reefs illustrate
that frequent disturbances prevent some communities from reaching an equilibrium determined by interspecific interactions
- changes in the coral reef community at Heron Island result from the effects of external disturbances that remove coral colonies from the reef, as well as internal processes that eliminate or establish colonies
= in these communities, growth and recruitment are slow processes and disturbances are frequent therefore, community never attains equilibrium and moderate levels of disturbance can foster high species richness
intermediate disturbance hypothesis
proposed by Connell in 1978
- species richness is greatest in communities experiencing fairly frequent disturbances of moderate intensity
- moderate disturbances create openings for r-selected species to arrive and join the community while allowing K-selected species to survive
communities that experience intermediate levels of disturbance contain
a rich mixture of species
where disturbances are severe and frequent
communities include only r-selected species that complete their life cycles between catastrophes
where disturbances are mild and rare,
communities are dominated by long-lived K-selected species that competitively exclude other species from the community
Colin R. Townsend and his colleagues studied what
- the effects of disturbance at 54 stream sites in the Taieri River system in New Zealand
- disturbance occurs in these communities
- measured amount of substrate moved in diff streambeds
= the results indicate that species richness is highest in areas that experience intermediate levels of disturbance
species-rich communities recover from disturbances…
more readily than less diverse communities
succession
ecosystems change over time in a process called succession
- the change from one community type to another
primary succession
- begins when organisms first colonize habitats without soil, such as those created by erupting volcanoes and retreating glaciers
- lichens are usually the first colonists and they derive nutrients from rain and weathering of bare rock, they secrete mild acids that erode rock surfaces that initiate the slow development of soil, which is enriched by the organic material lichens produce
- once lichens modify a site, mosses colonize patches of soil and grow quickly
- later successional stages are often dominated by K-selected species
climax community
long-lived species, which replace themselves over time, eventually dominate a community and new species join it only rarely
- this relatively stable, late successional stage is called a climax community
secondary succession
- occurs after existing vegetation is destroyed or disrupted by an environmental disturbance, such as a fire, storm, or human activity
- presence of soil make disturbed sites ripe for colonization and may contain numerous seeds that germinate after disturbance
aquatic succession
where debris from rivers and runoff accumulates in a pond, filling it to its margins
- ponds are first transformed into swamps, inhabited by plants adapted to a semisolid substrate
- as larger plants get established, their high transpiration rates dry the soil and allow other plants species to colonize
- the site may become a meadow or forest in which an area of moist, low-lying ground is the only remnant of the OG pond
microclimate
- climate of a small or restricted area
- because plants influence the physical environment below them, the community itself increasingly moderates its microclimate
- shade cast by a forest canopy helps retain soil moisture and reduce temperature fluctuations and wind speed
- but short vegetation
facilitation hypothesis
- suggests that species modify the local environment in ways that make it less suitable for themselves but more suitable for colonization by species typical of the next successional stage
inhibition hypothesis
- suggests that new species are prevented from occupying a community by species that are already present
- according to this hypothesis, succession is neither orderly nor predictable because each stage is dominated by the species that happened to have colonized the site first
tolerance hypothesis
asserts that succession proceeds because competitively superior species replace competitively inferior ones
- according to this model, early-stage species neither facilitate nor inhibit the growth of later-stage species
- as more species arrive at a site and resources become limiting, competition eliminates species that cannot harvest scarce resources successfully
- therefore, the climax community includes only strong competitors, tolerance may explain the species composition of many transitional and mature communities
disturbance climax
- disturbance can also inhibit successional change, establishing disturbance climax OR disclimax community
community that remains in non-equilibrium
2 large-scale patterns of species richness
1) latitudinal trends
2) island patterns
equilibrium theory of island biogeography
developed by MacArthur and Wilson
- explains variations in species richness on islands of different size and different levels of isolation
where do parasites gain energy from
a host species
symbiosis
occurs when one species has a physically close ecological association with another
why is commensalism rare in nature
because few species are unaffected by another
i.e. tree frogs using plants for protection (assuming the plant gets no general benefit)
Potato Cod from Great Barrier Reef in Australia
- striped cleaner wrasse will remove and eat ectoparasites attached to lip
- the cod will not eat the wrasse even if it could
= mutual benefit
the cod gets its food from consuming parasites, where the parasite gets to parasitize by chilling on the lip of the cod
Perils of mutualism
- mutualistic situations can place species on the edge of survival
- where one species depends entirely on another, the extinction of one must lead to change or the extinction of both
carnivore etmyology and herbivory etymology
carnivory: “caro” = meat
“ vorare” = to devour
herbivory: “herba” = green plants
what does predation lead to
evolution of defence mechanism
Fundamental niche of species 1 vs of species 2
Fundamental Niche of species 1
contains the realized niche of species 1 which is not restricted by species 2
Fundamental niche of species 2, contains the realized niche of species 2 which is restricted by species 1
area where the fundamental niches overlap they will have to have intense competition which isn’t ideal as its likely that they’ll both lose
what is the interactive hypothesis
- predicts that species within communities exhibit similar distribution along environmental gradients (indicated by the close alignment of several curves over each section of the gradient) and that boundaries between communities (indicated by arrows) are sharp
individualistic hypothesis
- predicts that species distributions along the gradient are independent (indicated by the alignment of the curves) and that sharp boundaries do not separate communities
observations of ecological gradients
- most gradient analyses support the individualistic hypothesis
- i.e. moisture gradients in Oregon and Arizona mountains
Species _______ reflects Species ________ and _________ of species
species DIVERSITY reflects species RICHNESS and RELATIVE ABUNDANCE of species
diversity: distinguish number of unique species to number of individuals per species
i.e. 5 different species, 20% of each so its even
richness: number of unique species
relative abundances: number of individuals per species
Succession after glacial retreat
1) the glacier retreated about 8m / year since 1794
2) the site was covered with ice less than 10 years before this photo was taken. when a glacier retreats, a constant flow of melt water leaches minerals, especially nitrogen, from the newly exposed substrate
3) once lichens and mosses have established themselves, mountain avens grows on the nutrient-poor soil. this pioneer species benefits from the activity of mutualistic nitrogen-fixing bacteria, spreading rapidly over glacial till
4) primary succession: within 20 years, shrubby willow, cottonwoods, and alders, take hold in drainage channels. These species are also symbiotic with nitrogen-fixing microorganisms
5) In time, young conifers, mostly hemlocks and spruce join the community
6) As the years progress, the smaller trees and shrubs are gradually replaced by larger trees
how do patterns of communities change during succession
1) r-selected species are short lived and K-selected species are long lived, species composition changes more rapidly in the early stages and more slowly in the later stages of succession
2) species richness increases rapidly during early stages because new species join the community faster than resident species become extinct
- later on they can stabilize or may even decline
3) in terrestrial communities receiving sufficient rainfall, the maximum height and total mass of the vegetation increase steadily as large species replace small ones, creating this complex structure of the climax community
how can animals show different patterns in succession
- as vegetation shifts, new resources become available and animal specie replace each other over time
- herbivorous insets, often with strict food preferences, undergo succession along with their food plants, and as herbivorous change, so do their predators, parasites, and parasitoids
- i.e. different vegetation will harbour a changing assortment of bird species
what factors are responsible for ecological succession
- dispersal abilities
- maturation rates
- lifespans among species are partly responsible for ecological succession
- early successional stages harbour many r-slected species because they produce numerous small seeds that colonize open habitats and grow quickly
- mature successional stages are dominated by K-selected species because they are long lived
- coexisting populations inevitably affect each other
when does species replacement occur
when individuals of dominant species die of old age or when an environmental disturbance reduces their numbers
- eventually, long-lived species replace short-lived species, but the precise species composition of a mature community is open to question
what factors affect succession
some combination of
- facilitation
- inhibition
- tolerance
- coupled with interspecific differences in:
DISPERSAL
GROWTH
MATURATION RATES
the patchiness of abiotic factors influence what
plant distributions and species composition
what factors play important roles in speeding successional change
disturbance and density-independent factors
i.e. moose prefer to feed on deciduous shrubs in northern forests, which accelerates the rate at which conifers replace deciduous shrubs
how can a disturbance climax be established
through inhibiting successional change
