22.3: Selection Pressures and Drivers

Botany Lab Manual · LibreTexts

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    From LibreTexts, under CC BY-NC 4.0, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.

    1. Competition for sunlight. Seedless vascular plants were able to reach heights up to 100 feet tall. In the lineage leading to the gymnosperms and angiosperms, some plants developed the ability to grow wider as they grew taller. This secondary growth allowed for increased stability and, eventually, to reach heights over 300 feet.
    2. Drought. Dry conditions would have selected for plants with thicker cuticles, leaves with less surface area to evaporate from, and propagules that could disperse without water and survive through dry periods to germinate when water was available.
    3. Herbivory. In addition to leaves that could resist drought, the presence of insects would have driven selection for plants that could defend against herbivory. The thick cuticle and tough texture of xerophytic leaves made them difficult to eat, while resin canals in both leaves and stems provided another line of defense.

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    This page titled 22.3: Selection Pressures and Drivers was last modified on Wed, 17 Jun 2020 21:53:26 GMT and is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Maria Morrow (ASCCC Open Educational Resources Initiative) .