INB 373 Exam 3 (lecture)

community

a group of interacting species that occur toegther in the same time and space

species interactions can be…

• positive

• negative

• neutral

predation

one species feed on or eats another species (±)

types of predation

• carnivory: animal eats animal

• herbivory: animal eats autotroph

• parasitism: symbiosis of parasite and host→ host is harmed not immediately killed

• parasitoid: symbiosis of parasitoid and host→ single host is always killed

optimal foraging theory

food benefits depends on encounter rate and handling time

• most carnivores are generalists→ low encounter rate + short handling time

• most herbivores are specialists→ high encounter rate + long handling time

herbivores look for more nutrient foods (leafs and seeds)

carnivore capture tactics & physical features

tactics?

• foraging, move: wolves, lions, shark

• wait & ambush: some snakes, eels

• set traps: spiders, antlions

physical features?

• speed

• teeth

• vemon

• tolerate posion

• mimicry

adaptations against carnivores

• large size (elephant)

• speed

• poisons (monarch butterfly)

• mimicry

• camouflage (peppered moths)

Batesian vs Mullerian Mimicry

Batesian: try to mimic species that is toxic but you are NOT toxic (king snakes mimics venomous coral snake)

Mullerian: unpalatable species tries to look more like another unpalatable speies (heliconias and monarch butterfly)

plant defense against herbivore

• structural (tough leafs, thorns)

• compensation (new growth)

• secondary metabolites (poison or compounds that attract predator)

Lotka-Volterra model

suggests that predator-prey populations have inherent tendency to cycle bc of abundance of one pop is dependent on the other

ex. Hare & Lynx populations

what prevents predators from driving prey to extinction?

• habitat complexitu and limited predator dispersal

• prey switching

  • spatial refuges

effects of predator-prey interaction

alter community interactions

**change outcome of competition→ remove starfish and mussels outcomepete all other competitors

endo vs ectoparasites

endo→ live in the intestinal tract or within host tissue/cell

ecto→ live in the outter body surface of the host

symbiosis

interaction between two different organisms living in close physical association

animal mechanisms against parasite

• protective other covering (skin)

• immune sustem (innate + adaptive)

plant mechanisms against parasite

• secondary metabolites

• resistance genes

• chemical signals to warn near by cells

parasite counter defense

• Parasitoid wasps

  • Host defense: some insects hosts can encapsulate endoparasites using specialised blood cells lamellocytes

  • Parasitoid wasps avoid encapsulation by injecting virus like particles that infect lamellocytes and cause them to self-destruct

• Plasmodium causes malaria

  • Mosquito→ vector that transfers sporozoite stage to humans

  • Human fence→ RBC dont import nutrients & infected RBC are destroyed by spleen

  • Plasmodium has genes for→ RBC transport proteins & make RBC “sticky” so they don't reach spleen

coevolution

populations of two interacting species evolve together, each in response to selection pressure imposed by the other

ex. gene-for-gene arms race between wheat and wheat rust→ wheat mutates to be resistant to wheat rust and wheat rusts mutates so wheat is no longer resistant

effects of parasites

• reduce survival, growth, reproduction of host

• population dynamics→ cycling of pop

• alter other species interactions→ too weak to hunt/defend

• alter ecological community→ weaken engineer species

competition

non-trophic interactions between individuals in which all parties are negatively affected by the reduced availability of a resource

Interspecific vs Intraspecific competition

• Interspecific: between members of different species

• Intraspecific: between individuals of a single species

resources & their limits

components of the environment that are required by species for growth, reproduction, and survival

multiple resource can be limiting but there is ONE most limiting resource

ex. water in drought, N/P in Hawaii

Fundamental vs realized niche

• Fundamental niche: full set of resources, plus other biotic and abiotic requirements of a species

  • ex. chipmunk species can survive over entire mountain

• Realized niche: restricted set of resources that a species is limited to due to species interactions

  • ex. chipmunk species only occupies very top of mountain bc competing for resources with 2 other chipmunk species

types of interspecific competition

• Interference competition→ direct interactions bt individuals where one species interferences with the ability of its competitors to use a limited resource

  • Ex. wolves and bear have aggressive interactions over access to wolf-killed prey

• Exploitation competition→ indirect interaction through one or more shared resources where individuals reduce the supply of a resource as they use it

  • Ex. cow and sheep– both eat same grass

• Apparent competition→ indirect interaction through one or more shared enemies

competition intensity depends on…

resource availability

is competition symmertrical?

effect of competition are often unequal or asymmetrical: one species is better at using resource, the other is harmed more than the other

amensalism

symbiotic relationship where one species is harmed while the other is unaffected

ex. cows step on grass when roaming

Lotka-Volterra Model of Competition— outcomes

1. Species 1 outcompetes species 2

2. Species 2 outcompetes species 1

3. Non-stable coexistence: either species might win

4. Stable coexistence

Lotka-Volterra Model of Competition— competitive exclusion principle & competitive coexistence

• competitive exclusion principle→ two species using a limiting resources in the same way cannot coexist

  • dominant species uses resources— inferior species locally extinct

• competitive coexistence: occurs when species use resources differently enough to avoid direct exclusion

Lotka-Volterra Model of Competition— stable coexistence when…

1. alpha and beta are equal or close to 1 (large

2. alpha and beta are small

alpha? effect of species 2 on species 1

beta? effect of species 1 on species 2

Gause 3 species conditions

• Competitive exclusion principle: two species that use a limiting resource in the sam way cannot coexist indefinitely

• Resource partitioning→ species using a limited resource in different ways are able to coexist

• Character displacement→ two species compete for resources, natural selection may favor phenotypes that allow them to partition their limiting resources– decreasing the intensity of competition

how can disturbances can alter the outcome of competition?

• Example. Algae vs Mussels

  • Brown also fugitive species (sea palm) coexist with mussels, a superior competitor, in rocky intertidal zone

  • Large waves sometimes remove mussels creating temporary opening of the algae

  • Low disturbance areas→ competition with mussels causes algae pops to decline or go extinct

fugitive species

they do well in recently disturbed zones, constantly need to move around

mutualism

mutually beneficial interactions between individuals of two species (+/+)

Ex. Pollinators & plants– food & higher reproductive rate

commensalism

individuals of one species benefits: individuals of the other species do not benefit but are not harmed (+/0 relationship)

ex. bacteria on human skin

types of mutualisms

• Trophic mutualism→ both species benefit through the exchange of energy or nutrients

  • ex. mycorrhizal fungi and plants — the fungi receive carbohydrates from the plant, while the plant gains enhanced access to soil nutrients

• Habitat mutualism→ one partner provides the other with shelter, living space, or favorable habitat

  • Example: Ants living in acacia trees — the tree provides shelter and nectar, while the ants defend the tree from herbivores

• Obligate vs facultative mutualisms

  • Obligate→ at least one species is entirely dependent on the other for survival or reproduction

    • ex. fig tree and wasps

  • Facultative→ both species benefit but are not dependent on each other for survival

    • ex. Bees pollinating various flowers

where are mutualisms more common/beneficial?

• positive interacts are more common in colder, more stressful environments

• more common in resource poor areas

mutualism— cheaters and penalties

Cheaters→ individuals that increase offspring production by overexploiting their mutualistic partner

If happens– interactions probably will not persist

Penalties→ imposed on cheater– these interaction are likely highly controlled in nature through selective pressures

Ex. yuccas and yucca moths→ obligate mutualism, flowers get aborted (penalty) when moths lay too many eggs (cheater)

ecological impact of mutualism

• influences the distribution of that species

• interaction on species diversity

• Example: Cleaner Fish

  • Eat from parasites from other fish

  • Removal of cleaner fish– overall species diversity of reef decreases

  • Heavy penalty of removing cleaner fish

landscape ecology

two communities interacting

how do we describe communities?

• Physical characteristics→ all species in a sand dune, mountain stream, or desert

• Biological characteristics→ all species associated with a kelp forest or a coral reef

• Question→ arbitrary

community structure

set of characteristics that shape communities

species diversity vs biodiveristy

• Species diversity→ is the most common measure of community structure

  • combine richness (# of species) and eveness (relative abundance)

• Biodiversity→ diversity at multiple scales from genes to species to communities

Shannon Diversity index

H=Higher value→ more diverse

flatter line→ more even community

combines relative abundance and evenness

species importnace

• foundation

• keystone

• ecosystem engineer

• redundant species→ have no specific role but add to diversity

Competitive networks

interactions among multiple species in which every species has a negative effect on every other species (comp) no one species dominated the interaction→ allowing coexistence

Competitive hierarchy

ordered ranking of species based on their ability to outcompete others

ex. species A always wins over B→ B always wins over C→ etc {false

agents of change

• Biotic agents: species interaction

  • Ecosystem engineers/keystone species influence community change

• Abiotic agents:

  • Disturbance→ events that physically injure or kill some individuals and create opp for other individual (ex/ tsunami)

    • sudden/short term

  • Stress→ abiotic factors that reduce growth, reproduction, or survival of individuals (ex. Increasing temp)

    • Long term

Abiotic and biotic factors often interaction to product community change (ex. Keystone engineer causes changes in abiotic conditions that result in species replacement)

succession

change in species composition in communities over time towards a climax community

types of succession

• Primary succession: colonization of habitats devoid of soil or soil-like material (volcanic rock)

  • Initial conditions are very inhospitable

  • Can be very slow

  • First colonizers (pioneer or early successional species) tend to be stress-tolerant

• Secondary succession: reestablishment of a community in which some, but not all, organisms have been destroyed

  • Often faster than primary succession

  • Secondary succession occurs after fores, storms, logging, etc

  • Legacy of preexisting species and their interactions with colonizing species play larger role than primary succession 

how to study primary succession

Space for time substitution→ assume that plant assemblages farthest from the lakes edge were the oldest, the nearest the lake were the youngest, representing a time series of successional stages

Chronosequence

observed a similar sequence of events in different succession environment

Example: primary succession in sand dunes in lake michigan by Henry Cowles 1899

• Marram grass→ dominated by various grades & forbes → dominated by various shrubs→ dominated by white pine stress→ dominated by deciduous broadleaved trees

• Climax community→ deciduous broadleaved trees

Example: secondary succession in abandoned field in North Carolina

• Dominated by annual forbs→ dominated by perennial grasses & forbes→ dominated by loblolly pine trees→ dominated by deciduous broadleaved trees

• Climax community→ deciduous broadleaved trees

how species interact during succession

• Facilitation of later species by earlier arriving species (usually +/-)

  • Ex. N fixation→ higher soil N benefits later species

  • Ex. slowing sand movement in a sand dune

• Inhibition of later species by earlier-arriving species (usually -/-)

  • Ex. first species prevent later species from settling in intertidal rocks

• Tolerance by later species of earlier-arriving species (usually 0/-)

  • Effect caused by early species and felt by later species

Early vs Late successional species

• What kind of life history do early successional species have?

  • Faster, shorter, smaller, many

• What kind of life histories do late successional species have?

  • Slower, longer, fewer, larger

Five successional stages: Glacier Bay, Alaska

1. Pioneer species establishment: dominated by lichens, mosses, horsetails, fireweed

2. Intermediate species: Dryas community develops→ N fixation

3. Forest regeneration: Alder stage→ dryas and alder are N fixers

4. Mature forest: Spruce forest→ most diverse stage

5. Climax community: Western hemlock→ climax is most resilient

how species interactions contribute to succession

• Facilitation interactions are often important drivers of early succession, especially when physical condition are stressful

• Inhibitors appear later species such as alders have negative effects on later species— comp important later on

• Tolerance→ spruce dominates due to slow growth and long life, succession is driven by life history characteristics

Competitive, facilitation and tolerant traits are all critical causes of successional stages at Glacier BayFacilitation interactions help early succession by enhancing conditions for later species, inhibition refers to negative impacts on later species, and tolerance informs how species coexist.

Alternative stable states

climax does not really exist→ multiple stable points

resilience vs resistance

• Resilience: ability to return to pre-condition

• Resistance: degree to which a system does not change under stress

Hysteresis

inability to shift back to OG community type even when original conditions are restored

stasis

temporary stability not necessarily full stop/climax

Drives of community change

• Interactions among species at the same trophic level

• herbivory (grazing)

• Fire

• Disturbances of all types

• introduction of new species

• Removal of species (top predators)

Biogeography

study of variation in species composition and ‘diversity’ across geographic location

‘Diversity’ richness— alpha, beta, gamma

• Regional scale: gamma diversity

  • What species do we find, where across the globe?

• Species turnover: Beta diversity

  • How many species do we gain or lose across an area?

• Local scale: alpha diversity

  • How many species are there in the local area?

continental drift

tectonic plates are sections of Earth's crust that move/drift through actions of current generated deep within the molten rock mantle

Latitudinal diversity gradient

Diversity increases towards the equator

higher latitude = lower diversity

Hypothesis proposed to explain LDG?

• Diversification Time→ Tropics are older and therefore have experienced  more speciation bc older region

• Diversification rate→ Tropics have more diversification/speciation events

• Productivity or carrying capacity→ Tropics have greater carrying capacity than temperate→ bc warmer temp and greater space so higher productivity

Island Biogeography

Species richness on islands is related to the size of the island and distance to the mainland

• Smaller island closer to mainland→ easier for orgs to find //colonize

• Large islands→ easier for orgs to find // colonize

• Small and far island→ hard to colonize

Equilibrium theory of island biography

• # of species on an island depends on a  balance between immigration (dispersal) rates and extinction rates

• New island species richness varies over time:

  • New species arrive by dispersal

  • Species go extinct on island

Mangrove islands

• Manipulated island Florida by spraying insecticide to remove all insects and spider

• After one year species # were similar to number found before experiment and islands closest to a source of colonizers had the most species

Krakatau test

• volcanic eruption wiped out all life on Krakatau→ scientists monitored bird species over time

• calculated immigration and extinction rates and predicted the island would support about 30 bird species at equilibrium, with a turnover rate of 1 species per year

• in 40 years, the island reached and maintained this predicted species richness, with an observed turnover of around 5 species.

Community membership depends on…

• Regional species pool

• Species dispersal ability

• Environmental conditions: abiotic filter

  • site too hot, too cold, too wet, too dry…

• Species interactions: biotic filter

  • Other species may prevent a species from joining a community→ biotic resistance

Intermediate disturbance hypothesis

Disturbances can keep the dominant competitor from reaching carrying capacity→ coexistence will be maintained

Species diversity will be greatest at intermediate levels of disturbance

• At low levels of disturbance, competition regulates diversity

• At high disturbance levels, many species cannot survive

ex. Study of communities on intertidal boulders that were overturned waves:

• Most large boulders has two species (rare disturbance→ competitive exclusion by late successional species)

• Intermediate size boulders had 4-7 species (intermediate disturbance, high richness)

• Small boulders were often overturned, most had one species (frequency disturbance, early successional species)

Importance of diversity?

Stability

→ long-standing idea in ecology is that species richness is positively related to community stability

Ex. Tilmen field study in cedar creek minnesota → Plots w/ higher species richness were better able to withstand drought than plots with lower species richness

Hypothesis on species richness and community function

• Complementarity hypothesis: a species richness increases, community function will increase linearity

  • Each species added has a unique and equally incremental effect

• Redundancy hypothesis: the functional contribution of additional species reaches a threshold

  • As more species added→ overlap in function→ redundancy among species

• Idiosyncratic hypothesis: strength of ecological function varies greatly– some species have large effect (foundation/keystone species), some have a minimal effect

landscape

an area which is spatially heterogeneous

ecologically this means multiple (at least 2) ecological communities with a decently large are of space

landscape ecology

study that examines how large scale patterns and ecological processes function together

Include: spatial patterns, processes, and dynamics of landscape

Influence: distribution and interactions of organisms, energy, and materials

Geographic Information Systems (GIS)

• Integrates spatial data from multiple sources

• How? 

  • Satellite for gathering imaging data

  • Aerial photography

  • Data gathered on the ground

• Why? Resource distribution and use, community distribution and function

• Ex. lark bunting (bird) → poor condition due to habitat loss and fragmentation

Landscape heterogeneity can be described in terms of composition and structure

• Landscape composition: kinds of elements (communities) or patches and how much of each kind is present

• Landscape structure: physical configuration of the landscape elements

  • Size of patches

  • Whether patches are aggregated or dispersed

  • Complexity of patch shape

  • Degree of fragmentation

landscape, ecology, and disturbances

1. Natural disturbances can shape landscape

2. Landscape affect ecological processes dispersal between patches

Biological Dynamics of Forest Fragments Project (BDFFP)

Brazil studies the effects of habitat fragmentation in the Amazon rainforest

findings?

• Fragmentation led to greater and more complex negative impacts

• Small fragments cannot sustain all their original species

• Edge effects, the surrounding matrix (non-forest areas), and connectivity between patches significantly influence biodiversity

edge effects

caused by fragmentation leading to increasing the amount of edges

• Increased wind disturbance→ increased tree mortality

• Invasion of disturbance-adapted beetles & plants

• Decreased soil moisture

• Increased air temp

• Increases phosphorus content of falling leaves

How effective are habitat corridors?

• Yes? Allow access to some resources

  • Ex. butterfly in woodlands→ connected patches allowed butterflies to do better in environment

• No? Increasing edge effects is bad

Core natural areas

assigned areas where conservation of biodiversity and ecological integrity take precedence over other uses

ex. Ex. Masoala National Park (madagascar) → successful conservation created core areas considering both ecological and socio-economic factors (local villagers)

buffer zones

areas with less stringent controls on land use but still provide habitat for many species→ sorround core areas

primary objectives for creating core areas

• Maintain the largest possible populations

• Provide habitat for species throughout their area of distribution

• Have enough area to maintain natural disturbance regimes

Conservation biology

the scientific study of biodiversity, how human activities impact it, and how to maintain it and prevent its loss

Successful management plans involve working with…

stakeholders

Ecological Society of America (ESA) vs Nature Conservancy

• Ecological Society of America (ESA)

  • Advances the science and practice of ecology and supports ecologist throughout careers

  • Increase scientific knowledge + foster thriving planet

• Nature Conservancy

  • Integrate science and advocacy and on the ground conservation

  • Non profit organization apply science to presence species and ecosystems

Global biodiversity crisis through taxonomic homogenization

ecosystems around the world become more similar to each other, often due to the spread of a few widespread species

distinct regional biodiversity declines, and we end up with fewer differences between ecosystems

current vs background extinction rates

• Background rate is losing one species every 200 years

  • Average species lifespan of 1-10 million years

• Current extinction rate is one species per yr

  • Humans have decreased average species lifespan

Umbrella species

protection of its habitat will serve as an ‘umbrella’ to protect many other species with similar habitat requirements

Usually have large ranges (grizzly bear) specialized habitats (red-cockaded woodpecker), or easy to count (butterfly)

secondary extinctions

When populations are lost from a community, there are consequences for that species predators, prey, and mutualistic partners

Ex. loss of bird pollinators reduces reproductive success in New Zealand shrub

Causes of loss of biodiversity

• Habitat loss

  • Ex. tropical deforestation to create terraced rice fields

• Habitat fragmentation

• Habitat degradation

• Change in disturbance regimes

• Pollution

• Overexploitation→ hunting/harvesting of natural pops at a rate that exceeds their ability to replenish their numbers

• Invasive species→ Increase # at the expense of native species— cause disease, outcompete

  • Ex. feral hog→ smart and non-native, aggressive, and big

approaches of conservation

• Population Viability Analysis (PVA): demographic modeling tool used to estimate a population’s risk of extinction under different scenarios and guide management decisions. It helps identify vulnerable life stages, determine minimum viable population sizes, and set sustainable harvest limits.

• Genetic Rescue – Florida Panthers: (90s) Florida panther population dropped to ~25 individuals, causing inbreeding and health issues→ introduce 8 Texas pumas increased genetic diversity, tripled the population, and reduced genetic defects, alongside habitat and road protection measures.

• Ex Situ Conservation: last-resort strategy where all known individuals of a species are moved to controlled environments like zoos or botanical gardens. While it can prevent extinction, it is costly, limited in capacity, and often doesn't allow for reintroduction into the wild.