Possible Interactions Species 1  Species 2 Species 2  Species Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease

Herbivory as a Tool Invasive Opuntia in Australia Impact of biocontrol insect Cactoblastis

Defenses against Herbivory Physical structures Trichomes Spines Non-digestible tissues Secondary chemical compounds Toxins Hard to digest chemicals (e.g., tannins)

Inducible Defenses

Possible Interactions Species 1  Species 2 Species 2  Species Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease

Seymeria cassioides Mistletoe Dodder Plant Parasites

Strangler Figs

Possible Interactions Species 1  Species 2 Species 2  Species Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease

Possible Interactions Species 1  Species 2 Species 2  Species Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease ?

Possible Interactions Species 1  Species 2 Species 2  Species Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease Ammensalism/ Allelopathy

Allelopathy: A controversial topic

Possible Interactions Species 1  Species 2 Species 2  Species Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease ? Ammensalism/ Allelopathy

Possible Interactions Species 1  Species 2 Species 2  Species Neutral Mutualism Commensalism Herbivory/ Parasitism/ Disease Ammensalism/ Allelopathy Competition

Competition between different species Potentially assymetrical! Light Space H20 Nutrients Space

Possible Interactions Species 1  Species 2 Species 2  Species Mutualism Commensalism Herbivory/ Parasitism/ Disease Neutral Ammensalism/ Allelopathy Competition

Experimental Studies of Competitive Interactoins

The Design Matrix Density of species i Density of species j

The Design Matrix Treatment combination indicating densities of both species i and j

The Design Matrix

Commonly Used Designs Partial AdditiveReplacement Series AdditiveComplete Additive

The Partial Additive Design Target species Competitor

The Partial Additive Design Commonly used design to study the impact of weeds on a crop plant

The Partial Additive Design Yield drops as density of competitor increases

The Partial Additive Design

Problems with the Partial Additive Design Target species only studied at one density Effects of density confounded with a change in the ratio between the two species Species 1 Species 2 Density Ratio 200 1: :2 50 0:1

The Replacement Series Design Density is fixed Ratio of two species systematically altered

The Replacement Series Design Species 1 Species 2 Treatment 1 Treatment 3 Treatment 2 Treatment 6 Treatment 5 Treatment 4 Density = 5

Monoculture Experiments as a Control

Monoculture treatment Replacement Series Experiment

Monoculture treatment Replacement Series Experiment Competition treatment Impact of Competition

Monoculture treatment Replacement Series Experiment Competition treatment Impact of Competition

Monoculture treatment Replacement Series Experiment Competition treatment Avena fatua has a large competitive effect A. barbata has little competitive effect

Monoculture treatment Replacement Series Experiment Competition treatment Assessing the interaction Total yield in treatment

Additive Competitive Effects I = J

Additive Competitive Effects I = J I > J

Additive Competitive Effects I = J I > J I < J

Non-Additive Competitive Effects Combined effects of competition have a greater negative effect than when plants are grown alone Species i has a bigger effect on species j than it has on itself Species j has a bigger effect on species i than it has on itself

Non-Additive Competitive Effects Combined effects of competition are less in combination than when plants are grown alone Both species impact themselves more than their competitor does

A Non-Additive Example Relative yield total = Sum of yields in competition Sum of yields in monoculture

A Non-Additive Example