MIS Lectures 3-4

Where are invasions likely?: NIS attributes

vector/propagule supply, high growth/colonization rates (r selected species), higher resource use efficiency, trait plasticity

where are invasions likely?: recipient community attributes

species diversity, resource availability, disturbances in ecology

niche concept

organisms environmental requirements (living and non living)

n dimensional

includes as many requirements as organism needs to survive (empty niches rarely seen, disturbances may open up niches)

fundamental vs realized niche

fundamental: all combos of conditions a species could occupy, realized: actual combo of conditions a species occupies, adds in competition factor)

Crab example

abiotic factors: water temp, salinity, habitat, tides, pH, oxygen availability

biotic: predators/prey, competition, parasitism/disease

Elton’s biotic resistance hypothesis

expect lower invasion in species rich communities (less opportunity for invasive species to establish, less niches available)

sampling effect

as species diversity within a patch increases, so does the chance a patch contains a species that provides biotic resistance (through competition or predation)

Niche complementary

diversity enhances native species community stability across conditions

disturbances

events that cause mortality or change in resource availability for 1 or more species (unpredictable, vary widely in scale/intensity

intermediate disturbance hypothesis

moderate disturbances prevent competitive exclusion, found in communities structured by competition/colonization tradeoffs (key in sessile communities to replenish the area)

biotic resistance

disturbance leads to resource opportunity for invasive tunicates

factors influencing invasive species establishment

species richness, available space, percent of native species in the community

factors influencing invasive species

communities with higher resource availability can support more species (and more invasive species)

effects of invasive species on ecosystems

direct competition with native species, loss of species diversity (natives can become endangered), disrupt natural food web, affect nutrient/water cycles

competition and invasion success

successful when: strong competitors for food and shelter, direct predation/smothering on native species, functionally similar native species are absent or uncommon, utilize resources differently from natives, fill empty niches- example: coral killing sponge by smothering

enemy release hypothesis

successful invaders perform better in invaded ranges (grow bigger and reproduce more) because they lose natural predators and parasites

evolution of increased competitive abilities

in native range: natural enemies present, invest in defenses, competition is balanced

introduced range: competition tipped, natural enemies not present, invest less in defenses and increased investment in reproduction

Darwins novel weapons hypothesis

in native range: competitors co-evolve, weapons are less effective

introduced range: native competitors naive, weapons are effective

parasite transfer

many lost during invasion process, some can spread to new native species (parasite spillover)

island biogeography

islands are smaller and isolated, unique habitats for testing

endemic species

specific habitat, only found there (due to humidity, temp, etc.), usually lack predators and have lower genetic diversity (can cause native species to become locally extinct)

invasion meltdown hypothesis

establishment of first species (often ecosystem engineers) facilitates invasions of other species

Positive effects of NIS on native species

at beginning of oyster establishment, mussels provide a substrate to settle on. after larval attachment to mussels, oysters smother the mussels. with increasing oyster abundance and size, oyster larvae tend to prefer settlement on oyster beds, mussels can now hide under the oysters (changed from competitive displacement to accommodation)