Botanical Structures: Plants have evolved many structural adaptations to deal with climate, reproductive needs, and other environmental factors. Structures: Seeds Fruits Flowers Leaves Stems Roots Photosynthetic pathways etc. Plant Predators: Predation benefits the predator, but not the prey (+ - interaction). Plant predation (herbivory, defoliation) takes various forms: Parasites : for example, aphids (suck plant sap) Grazers : for example, deer defoliate parts of plant (eat it). In the case of grass, this can actually stimulate growth because old matter is removed and the meristem (point of plant growth) is at the base of leaf is able to produce new growth. Meristem at base Aphids Deer Grass + + - Plant Defense: Plants have evolved defenses due to stress caused by predators. Defensive responses to predatory stress: Structural Defenses Chemical Defenses Mimicry Predator Satiation Passion flower mimics butterfly egg so leaf appears taken Intraspecific Competition: Stress is also caused by increased competition (- - interaction) due to high population density. (Intraspecific competition is between members of the same species). Responses to competitive stress: Organisms can minimize stress with dispersal. Especially young organisms or when desirable environments are available. -- Interspecific Interactions : Competition is a negative interaction (- -) for all organisms. So organisms evolve to minimize competition. (Interspecific competition is between members of different species). Evolution leads to symbiotic interactions between species. Interactions: Mutualism (+ +) A remarkable 3-way mutualism appears to have evolved between an ant, a butterfly caterpillar, and an acacia in the American southwest. The caterpillars have nectar organs which the ants drink from, and the acacia tolerates the feeding caterpillars. The ants appear to provide some protection for both plant and caterpillar. An example of commensalism in the rainforest is the tremendous numbers of vines, mosses, lichens and climbing plants that use the trunks and branches of trees for support or substrate. Commensalism (+ 0) Interspecific Interactions : Competition is a negative interaction (- -) for all organisms. So plants evolve to minimize competition. Evolution leads to the formation of new species with specialized niches. Resource Partitioning: Niches minimize competition by separating organisms in space and time. An example of this is resource partitioning. Interspecific Interactions : Competition is a negative interaction (- -) for all organisms. So plants evolve to minimize competition A rainforest is a good example of how interactions among plant species can lead to resource partitioning. There is intense competition (- - interaction) for light. All plants lose as they use their energy to grow towards light. Some plants are selected for (emergent layer) and exclude others from best light areas. Plants in lower light areas (understory, forest floor) have evolved to make this their niche--broadening their leaves, maximizing growth during high-light times, etc.