Species InteractionsSpecies Interactions

Important in determining –•population dynamics•community composition•landscape spatial pattern •ecosystem function

T. Kittel, W. BowmanUniv of Colorado

General Categories

Assigned by effect on the two individual organisms interacting:

+, + = mutualism N2 fixation, mycorrhizae

+, 0 = commensalism Nurse plants

– , 0/+ = amensalism Allelopathy

–, + = parasitism herbivory / predation

–, – = competition Intra & interspecific

Think about these interactions in the context of species geography!

Can be more complicated than direct interactions of 2 individuals

mediated through a 3rd individual or species • soil microbes, herbivores influence competitive

interactions

A. Mutualism (+, +)

Plant-Microbe

•Mycorrhizae•N–fixation•Lichen

Rhinoceros Hornbill eating Strangler Fig fruits, Borneo

Mucuna holtonii, Central America

Plant-Animal

•Pollination

•Insects•Birds

• Hummingbirds•Bats

•Fruit dispersal

•Defense•Ants

Azteca Ants on Cecropai, Panama

“The Forgotten Pollinators”Rufous Hummingbird

Monarch Butterfly

White-winged Dove

Arizona-Sonoran Desert Museumwww.desertmuseum.org/pollination/

Lesser Long-nosed Bat

“Nectar corridors”•Sequence of flowering

plants

Long–distance migratory pollinators•Threatened – habitat loss•Keystone species

moss v. lichenAtlantic Forest, Brazil

B. Commensalism (+,0)

Plant-Plant

1) Vines

2) Epiphytes

•Bromeliads•Orchids•Cacti

•Ferns•Lichen•Moss•Algae

Staghorn fern

Exceptions – Commensalism goes

to Mutualism –

Lichen with cyanobacteria: N leaching, benefit to tree

goes bad –

Competition

• Strangulation • Overtopping

Detrimental overburden

Strangler fig

Pueraria montana var. lobata

Kudzu – “the vine that ate the south”

• Introduced 1876 from Asia• Planted for soil conservation 1930’s

Oriental Bittersweet

• Vine, introduced from e. Asia• Invasion in eastern US

Celastrus orbiculata

2) Nurse plants

• Saguaros under Palo Verde

• Desert annuals under shrubs

A. Commensalism – continued

• Piñon pine under Sagebrush

Plant-animal commensalism – Habitat

Oropendola nests, Roraima Brazil

Titi monkey, São Paulo Brazil

Red-footed Booby in MangroveGalápagos Is.

Iran Jaya's People of the Trees

• nesting• roosting• hunting for other animals• shelter from other animals

C. Amensalism (– , 0/+)

Allelochemical Interactions

•Plant–Plant•Allelopathy

Larrea tridentata - Creosote

• Plant–Animal • Herbivory defenses

Big sagebrush with native bunchgrasses growing under

canopy

Difficult to show in field

• Plant–Decomposer• Litter composition soil pH soil biota:

Conifer low pH fungi favored, Temperate Deciduous neutral

bacteria• Plant leakage of compounds detrimental to soil biota

D. Parasitism (–,+)

Dodder (Cuscuta) –

•stem parasite•no chlorophyll = holoparasite

Coral root orchid - Corallarhiza maculata root parasite on pines

Mistletoe –

•stem parasite•differing degrees of chlorophyll

•with chlorophyll = hemiparasite•w/o holoparasite

Arceuthobium americanumCarpellate plant on Pinus contorta

Arceuthobium cyanocarpumStaminate plant (left) and carpellate plant (right) on Pinus ponderosa

Dwarf mistletoe – holoparasite

Broadleaf (Hairy) mistletoe - hemiparasite

Phoradendron tomentosum on hackberry (Celtis laevigata), preferred host

More hemiparasites:

•Indian paintbrush – Castilleja spp.

•Root parasite

Inference of species interactions on the landscape

• If species interactions are important to plant species – Should be reflected in the spatial patterns of individuals (inter and intraspecific)• if mutualisms among plant species occur, should be a

positive associationthey should occur closer together (clumped) than predicted by chance (random)

Landscape spatial patterning (con’t)

• if amensalism occurs, should be pushed away from each other giving an even distribution

Larrea tridentata - Creosote

Landscape spatial patterning (con’t)

• Under competition – competitive exclusion leads to • range separation • niche partitioning

Non-overlapping geographic ranges of five species of large kangaroo rats

Within–canopy distribution

Amazonian tree –

The long roots dangling from the crown probably belong to Philodendrons

On the middle and upper branches cluster groups of orchids, bromeliads, and ferns – including staghorn fern

Low on the trunk are Arums & Philodendrons with heart-shaped leaves

Keystone species

• Presence of a species determines community structure disproportionately to population size

Summary – Species Interactions

Plants and animals engaged in interactions with wide range of other taxa

Positive, detrimental, or neutral effects of one species on another

Reflected in spatial patterns – random vs. even vs. uniform

Reflected in community structure – Keystone species