Lecture 21 - Living on Land (Ecology of Land Plants)

03/07/25

why are seed plants more diverse than seedless plants

• seed dispersal is more effective than spore dispersal because it is only through wind

• pollen also increases genetic recombination

angiosperm vs gymnosperm

angiosperm

• has flowers to attract pollinators

• fruits surround seeds and help with dispersal

• mutualisms with animals help to increase fitness

how does mutualism drive angiosperm diversity

• flowers are specialized shoots with modified leaves

• fruits are modified ovaries

  • when their ovules are fertilizes, the ovary walls thicken

• flowers and fruits are under selection by animal mutualists

how is plant landscape changing

seedless vascular plants used to be dominant, so the microbes that break down lignin and cellulose hadn’t evolved yet (meaning there was just giant dead trees everywhere because they didn’t fully decay and just turned into coal)

they were replaced by gymnosperms and then angiosperms became dominant in milder climates

how are plants used as medicine

• treating pain (aspirin, oxytocin)

• treating cancer (taxol)

• treating heart disease (digoxin)

plant ecology interactions

plant-plant

• competition, facilitation, allelopathy

plant-fungi

• mycorrhizae

plant-animal

• pollinators, dispensers, herbivores

plant-fungal mutualism: mycorrhizae

symbiotic relationship between fungi and 90% of plant species

fungi increase the nutrient uptake for plants, and plants provide carbohydrates for fungi

how did mycorrhizae help early plants live on land

early plants lacked roots so it was difficult to extract nutrients from soil

plant-animal mutualisms

flowers and fruits led to many interactions such as pollination (movement of pollen through animals increases chance of mating), seed/fruit dispersal (after animals eat fruit and drop seeds somewhere

plant-animal antagonism: herbivory

herbivores significantly impact plant fitness so plants produce physical and chemical defense (secondary metabolites - which we look for when making medicine to prevent herbivory) or develop mutualisms with bodyguards