Species Interactions
Important in determining –
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population dynamics
community composition
landscape spatial pattern
ecosystem function
T. Kittel, W. Bowman
Univ of Colorado
General Categories
Assigned by effect on the two individual organisms interacting:
+, + = mutualism
+, 0 = commensalism
– , 0/+ = amensalism
–, +
= parasitism
N2 fixation, mycorrhizae
Nurse plants
Allelopathy
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
Plant-Animal
• Pollination
Rhinoceros Hornbill eating
Strangler Fig fruits, Borneo
Mucuna holtonii, Central America
• Insects
• Birds
• Hummingbirds
• Bats
• Fruit dispersal
• Defense
• Ants
Azteca Ants on Cecropai, Panama
Rufous Hummingbird
“The Forgotten Pollinators”
Lesser Long-nosed Bat
Long–distance migratory pollinators
• Threatened – habitat loss
• Keystone species
“Nectar corridors”
• Sequence of flowering plants
Monarch Butterfly
White-winged Dove
Arizona-Sonoran Desert Museum
www.desertmuseum.org/pollination/
B. Commensalism (+,0)
Plant-Plant
1) Vines
2) Epiphytes
• Bromeliads
• Orchids
• Cacti
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Ferns
Lichen
Moss
Algae
moss v. lichen
Atlantic Forest, Brazil
Staghorn fern
Exceptions – Commensalism goes
to Mutualism –
Lichen with cyanobacteria: N
leaching, benefit to tree
 goes bad –
Detrimental overburden
Competition
• Strangulation
• Overtopping
Strangler fig
Kudzu
– “the vine that ate the south”
• Introduced 1876 from Asia
• Planted for soil conservation 1930’s
Pueraria montana var. lobata
Oriental Bittersweet
• Vine, introduced from e. Asia
• Invasion in eastern US
Celastrus orbiculata
A. Commensalism – continued
2) Nurse plants
• Saguaros under Palo Verde
• Desert annuals under shrubs
• Piñon pine under Sagebrush
Plant-animal commensalism – Habitat
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nesting
roosting
hunting for other animals
shelter from other animals
Red-footed Booby in Mangrove
Galápagos Is.
Oropendola nests, Roraima Brazil
Iran Jaya's People of the Trees
Titi monkey, São Paulo Brazil
C. Amensalism (– , 0/+)
Allelochemical Interactions
• Plant–Plant
• Allelopathy
Larrea tridentata - Creosote
 Difficult to show in field
• Plant–Animal
• Herbivory defenses
Big sagebrush with
native bunchgrasses growing under
canopy
• 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
Arceuthobium americanum
Carpellate plant on Pinus contorta
Mistletoe –
• stem parasite
• differing degrees of chlorophyll
• with chlorophyll = hemiparasite
• w/o  holoparasite
Dwarf mistletoe – holoparasite
Arceuthobium cyanocarpum
Staminate plant (left) and carpellate plant (right)
on Pinus ponderosa
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 association
 they 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
on the trunk are Arums &
Philodendrons with heart-shaped leaves
 Low
Keystone species
• Presence of a species determines community structure
disproportionately to population size
Summary – Species Interactions
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Plants and animals engaged in interactions with wide range of
other taxa
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Positive, detrimental, or neutral effects of one species on another
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Reflected in spatial patterns – random vs. even vs. uniform
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Reflected in community structure – Keystone species