Topic 5

Zonation

Where each species flourishes based on their different tolerance ranges for temperature, moisture availability, changing abiotic conditions as well as different abilities to compete w/other species for resources

• can be determined by natural boundaries

Ectone

Sharp changes in environmental conditions over a relatively short distance, accompanied by a major change in the composition of species which creates a boundary

Interdependent communities

Species depend on each other to exist

• moving from one community to the next there will be a whole new composition of species not a gradual gradient

Independent communities

Species do not depend on each other to exist

• composed of species that live in the same in the same place because they have similar adaptations and habitat requirements

• Dominant system found in the wild

Keystone species

Substantially effect the structure of communities even when individuals of that species may not be particularly numerous

• removing a keystone species can cause a community to collapse

• They usually increase and maintain species diversity

• Sea stars, sea otters, gray wolves, bumble bees

Direct effect

Indirect effect

When 2 species interact without involving other species

When two species interact in a way that involves one or more intermediate species

Trophic cascade

When indirect effects are initiated by a predator

Density mediated Indirect Effects

• indirect effects caused by changes in the density of an intermediate species

• High density of sea stars in intertidal community can decrease in mussels which allows other species to occupy limited open space on rocks

Trait mediated Indirect Effects

Indirect effects caused by changes in the traits of an intermediate species

• happens when a predator causes its prey to change its feeding behavior which in turn alters the amount of food consumed by the prey

Bottom up Control

The abundances of trophic groups in a community is determined by the amount of energy available from the producers in that community

Top down control

Abundance of trophic groups is determined by existence of predators at the top of the food web

Accounting for diversity

• productivity measured in terms of biomass of producers or consumers over time

• Most common relationship across productivity vs richness studies is that where there is medium productivity ther is high species richness compared to sites with either high or low productivity

• Added fertility causes decrease in species richness of producers while biomass increases

• Keystone species increase richness

Intermediate disturbance hypothesis

Tells us that mores species are present in a community that experiences occasional disturbances than in a community that experiences frequent or rare disturbances

Succession

Process in a community that is the change in species composition over time

• each stage during the process of succession is known as the seral stage

• Pioneer species- earliest species to arrive at a site→ typically have the ability to disperse long distances and arrive quickly at a disturbed environment

• Climax community- final seral stage in succession→ composed of the group of organisms that dominate a given biome

Primary succession

Development of communities in habitats that are initially devoid of plants and organic soil such as sand dunes, lava flows and bare rock

Secondary succession

Development of communities in habitats that contain no plants but do have organic soil

• occurs in fields that have been plowed or forests that have been uprooted by a hurricane

• Well developed soils with plant roots and seeds that contribute to rapid growth after distrubance

Facilitation

Mechanism of succession in which the presence of one species increases the probability that a second species can become established

• they alter the environmental conditions of the site which makes it more suitable for other species to establish and less suitable for themselves

Inhibition

Mechanisms in which one species decreases the probability that a second species will establish due to competition, predation, and parasitism

• can prevent movement towards a climax community

Tolerance

Mechanism of succession in which the probability that a species can become established depends on its dispersal ability and its ability to persist under the physical conditions of the environment

• dont alter environment in ways that help or inhibit other species but eventually will be affected by other species

Pioneer species characteristics

• lichens and mosses that require no soil and can live on rocks

• Drought tolerant grasses that can colonize dry sand dunes

• They produce buts of organic matter that combine with rock weathering to create soils

• At the end of succession large trees will dominate

Intertidal succession

• Occurs more quickly→ generation time of dominant species is much shorter

• Powerful waves occur that can remove organisms

• Ulva là tu a came to dominate and blocked red algae but attracted crabs to eat it so then red algae came to dominate

Lake succession

• created by receding glacier→ basin full of water

• Overtime erosion of soil and growth/death of organisms for sediments and fill basin

• Plants extend into water and form floating mat of vegetation and underneath partially dead vegetation builds up forming peat

• Microbial decomposition is slow because the water underneath has low oxygen levels

Lake Michigan Succesion

• abandoned field colonized by asters, horsewood, and goldenrod

• San dune by beach grass and bluestem which stabilize sand dunes and add organic matter to the soil

• Wetlands have cattails which produce OM that allow terrestrial plants to colonize after many years

Community stability and resistance

Ability of a community to maintain a particular composition based on community resistance

Community resistance- measure of how much a community changes when acted upon by some disturbance like addition or removal of species

Community resilience

Ability of a community to return to its original state after being disturbed

• Increased amount of plant species increases stability of herbivore richness and abundance

• Communities with high plant diversity provide more consistently available food and habitat for herbivores, predators, and parasitoids

Alternative stable states

When a stable community is perturbed so much that species composition and relative abundance of populations in a community change→ new community structure

• requires large disturbance like removal of keystone species or dramatic change in environment

• Biomes where fires occurs regularly favor this, in aquatic environments high levels of nutrients can cause

Landscape ecology

Focused on spatial arrangement of habitats at different scales and how this influences individuals, populations, communities, and ecosystems

Habitat Heterogeneity

Reflects recent and historical events caused by both natural forces and human activities

Legacy affects

Historical processes that have long lasting influences on current ecology of a known area

• eskers are legacy effects of glaciers

Diversity and heterogeneity

• heterogeneity of habitat types across the landscape of streams supports a higher richness of bird species than any single habitat, conserving a variety of habitats over a large area is critical to conservation of increased bird species diversity

Alpha, Beta, and Gamma diversity

Alpha- local diversity, number of species in a relatively small area of homogenous habitat

Gamma- regional diversity, number of species in all habitats that comprise a large geographic area

Beta- number of species that differ in occurrence btw two local habitats

• stream A has 5 species, steam B has 3 that are different, the streams have a B diversity of 8

Species Area Relationships

• Larger areas tend to contain more species

• Species area curve: graphical relationship in which increased area is associated with increased number of species S=cA^z

• To make it easier to graph take the log of both sides log S= log c + z log A

Ecological Effects of Habitat Fragmentation

• total amount of habitat decreases

• Number of habitat patches increase

• Average patche size decreases

• Amount of edge habitat increases

• Patch isolation increases

• Habitat matrix increases

Island and arthropod experiment

• experiment with tiny islands off the keys

• Tents were built over select islands and they were fumigated w/insecticide that killed almost every arthropod

• removed tents and gathered data every few weeks for a year→ each island was rapidly recolonized by arthropods

• Species richness was similar levels to before fumigation even though the composition was different→ isolation was key factor in how many species could live on an island

Equilibrium theory of island biogeography theory

• number of species on an island reflects balance between the colonization of new species and extinction of existing species

• Rate of new species colonizing an island decreases as a function of how many species have already colonized it

• As more species live on the island its more possible for them to go extinct so rate increases

• Predicts number of species present at equilibrium not particular composition of species

Latitudinal trends of Biodiversity

• in northern hemisphere, number of species in most groups of animals and plants increases from north to south

• Number of mammals and birds increases from east to west in N.A bc greater amounts of habitat heterogeneity in extensive mountain ranges

• Reptiles decline towards the north

• Amphibians and trees are more diversity in the east

• Increased species richness as you go closer to the equator