Population and Community Ecology

Complexity of nature Population: all inviduals that belong to the same species and live in a given area at a particular time Community: all of the populations within a given area; used to see how species interact with one another Ecosystem: all of the biotic and abiotic components in a particular location; used to study flows of energy and matter Biosphere: all of earth’s ecosystems; used to study movement of water, air and heat around the globe

Population Ecology “study of factors that cause populations to increase or decrease Population Size a. (births and immigration) - (deaths and emigration)

Population Characteristics Population size Population density Population distribution Population sex ratio Population age structure

Population Size Total number of individuals within a given area at a particular time Dependent upon density-dependent and density-independent factors Density dependent - depends on how dense the population is - limiting resources ex) plants – nitrogen and phosphorus animals - food - carrying capacity( K): helps in predicting how many individuals a population can sustain Limiting resource: a resource that a population cannot live without and which occurs in quantities lower than the population would require to increase in size http://www.algebralab.org/practice/practice.aspx?file=Reading_CarryingCapacity.xml

d. density-independent factors - does not depend on how dense the population is - ex) tornado, floods, fires

Population Density Number of individuals per unit of area Helps scientists estimate if a species is rare

Population Distribution How individuals are distributed throughout Random, uniform, clustered http://kids.britannica.com/comptons/art-108151/The-way-a-population-is-spaced-across-an-area-is

Population Age Structure How many individuals fit into a particular age category Predicts how rapidly a population will grow Population with a large proportion of old individuals are with a large population of individuals that are too young to reproduce will produce fewer offspring that a population that has a large proportion of individuals of reproductive age http://www.geography.hunter.cuny.edu/~tbw/ncc/Notes/Chapter6.pop/chapter.6.pop.age.structure.outline.html

Population Growth Models Growth rate – (births – deaths) in a given time period - intrinsic growth rate * unlimited resources available (r) * high population growth rate b. Exponential growth model - rapid growth - j shaped curve - continuously increase population growing at a fixed rate Exponential growth: under ideal conditions, the future size of the population depends on the current size of the population, the intrinsic growth rate and the amount of time over which the population grows * Real populations can grow exponentially at first but over time they will reach a carrying capacity http://biology.unm.edu/ccouncil/Biology_112/Summaries/Pop_Growth_and_Reg.html

c. Logistic growth model (k) - incorporates limits on population growth (limiting resources) - s shaped curve - predicts population growth subject to density-dependent constraints - overshoot - die-offs (population crash) - predation (lynx and the hare) Initially exponential and then reaches carrying capacity http://cnx.org/content/m45553/latest/

Reproductive Strategies and Survivorship curves K-selected species (elephant) - low intrinsic growth rate - large organisms, late reproductive maturity, produce few offspring, provide parental care b. R-selected species (dandelions, house mice) - high intrinsic growth - rapid population growth with overshoots and die-offs - small organisms, early reproductive maturity, reproduce frequently with lots of offspring, little or no parental care Population size most commonly increases through reproduction Elephants are example of k-selected species Endangered k-species cannot respond quickly to efforts to save it from extinction

c. Survivorship curve – distinct patterns of survival over time K-selected species: high survival rates throughout most of their lifespan but as they get older, they start to die off (TYPE I) - elephant R-selected species: low suvivorship early in life and very few reach adulthood (TYPE III) - mosquito Squirrels experience TYPE II where there is a constant decline in survivorship throughout their lifespan http://www.uic.edu/classes/bios/bios101/x306_files/textmostly/slide12.html

Community Ecology Species distribution - 3 factors * fundamental niche * ability to disperse * interactions with other species (community ecology)  competition, predation, mutualism, commensalism

Competition “struggle of individuals to obtain a limiting resource” Competitive Exclusion Principle - two species competing for the same limiting resource cannot coexist - having the same realized niche can lead to extinction of one species

b. Resource partitioning - two species divide a resource based on behavior and morphology - ex) birds that eat different seeds - 3 types * temporal * spatial * morphological Temporal – utilizes same resource but at different times of the day Spatial – using different habitats for the same resource Morphological – darwin’s finches Overall: reduces competition for limiting resources

PREDATION One species as a resource of another species Four types - true predators - herbivores - parasites - parasitoids C. lynx-hare relationship D. Defenses - hiding, reduced movement, chemical toxins, thorns, camouflage True predators – kill their prey and consume most of what they kill Herbivores – consume plants as prey; eat only a small fraction without killing it Parasites – live in or on an organism (host); rarely cause death of host Parasitoid – lays eggs within host and they slowly consume host from inside out leading to death http://www.zimbio.com/Nick+Miller/articles/ne-i0DfjTAV/Population+Dynamics+Mammals+Part+2+Nick+Miller

Mutualism “benefits two interacting species by increasing both species’ chances of survival or reproduction” Examples - pollination - coral reefs and algae - acacia trees and ants http://www.marietta.edu/~biol/biomes/symbiosis.htm Acacia tree provides a home for the ants and the ants protect the tree from any predators (herbivores or other plants)

Commensalism “one species benefits but the other is neither harmed nor helped” Example - birds using trees as a perch http://ibc.lynxeds.com/photo/mountain-elaenia-elaenia-frantzii/bird-sitting-small-tree-branch

Keystone Species “species that plays an important role in its community” Exist in low numbers Types a. predators b. sources of food c. mutualistic species d. provider of other essential services

a. sea stars (Pisaster ochraceus) b. flying fox Examples a. sea stars (Pisaster ochraceus) b. flying fox c. beavers (ecosystem engineer) Sea stars – prey on mussels which clears space for other species to attach on the rocks Flying fox – only pollinator and seed disperser for hundreds of tropical plant species Beavers – creates habitat for other species (ecosystem engineer); create dams that convert narrow streams into large ponds, ponds may flood causing trees to die and then creating a habitat for animals that rely on dead trees

Succession Ecological succession – predictable replacement of one group of species by another group of species over time Primary Succession a. surfaces that are devoid of soil Steps: Bare rock is colonized by algae, lichens (can survive with little or no soil) Once these are dead, they become organic matter that allows soil to be created Soil develops on bare surface and can now allow for deep rooted plants to survive First, there are mid-successional plants such as grasses and wildflowers (helps bring up nutrients in the soil) New species colonize the area and outcompete the mid-successional plants Eventually, it is colonized by bigger trees and plant species http://bcs.whfreeman.com/friedlandapes/#668210__690861__

a. areas that have been disturbed but have not lost their soil Secondary Succession a. areas that have been disturbed but have not lost their soil b. pioneer species Pioneer species: trees such as the aspen because of their ability to colonize new areas rapidly and grow well in full sunshine (these trees can disperse easily as well) http://bcs.whfreeman.com/friedlandapes/#668210__690861__

Factors affecting Species Richness Determined by a. colonization of the area by new species b. speciation within the area c. losses from the area by extinction Factors above are influenced by a. latitude b. time c. habitat size d. habitat distance Species richness: # of species in a given area

Latitude a. the further away from the equator, the number of species decline b. no known reason Time a. longer a habitat exists, the more species there will be (colonization, speciation and extinction)

Habitat size and distance a. “Theory of Island Biogeography” - size: larger habitats contain more species * dispersing species are more likely to find larger habitats * larger habitats are less prone to extinction * larger habitats contain wider range of environmental conditions - distance: * islands further from land contain fewer species Species are more likely able to disperse short distances than they are longer distances