Better if Browsed?


Behold the glory and splendor of scarlet gilia (Ipomopsis aggregata)! This gorgeous species is native to much of western North America from British Columbia south to Texas. Far from being just a beautiful red wildflower, scarlet gilia has some life history traits that are quite fascinating. Did you know that there is some evidence to suggest that this species actually benefits from natural levels of herbivory?

We are all too familiar with herbivore damage. Countless times I have been awaiting a bloom to burst only to have the buds nipped off the night before they opened. While this can be devastating to most plant life (not to mention my sanity), for scarlet gilia, an encounter with a hungry deer may actually increase its reproductive fitness! Scarlet gilia is most often a biennial. It spends its first year photosynthesizing as a rosette, saving up energy for next year's reproductive effort. Starting in July of its second year, most scarlet gilia will throw up a single flower stalk. In at least one study, 77% of flowering plants were dined upon. Whereas this would spell disaster for most other flowering plants, the removal of the single flower stalk stimulates the production of, on average, 5 new flowering stalks.

Each new flowering stalk sees no decrease in fitness either. This means that each plant that gets browsed subsequently benefits from a five fold increase in reproductive ability. Interestingly enough, plants that have already been browsed once don't seem to be browsed again. It is believed that the initial browsing signals the plant to begin producing secondary compounds that render its tissues either distasteful or even toxic. Some authors suggest that this increase in fitness due to herbivory is site specific and only will occur at highly productive areas. More work needs to be done to shed light on this matter.

Just when you thought scarlet gilia couldn't get any cooler, now we will consider pollinators. A cursory glance will suggest that the long, red, tubular flowers are pollinated by hummingbirds. This is true, at least for part of the year. Scarlet gilia blooms from July through September but its hummingbird pollinators are gone by the end of August. Why would the plant continue to flower after its pollinators have left? If you were to watch a patch of scarlet gilia from July until September, you would notice that, on average, flowers produced from July to August are deeper red than those produced after August, which are much paler with white spots. 

What is happening is the plant is switching its cues. Whereas hummingbirds are attracted to red, moths on the other hand are attracted to flowers towards the white end of the spectrum. After the hummingbirds migrate south, scarlet gilia produce lighter colored flowers to take advantage of white-lined sphinx moths, which are available for pollination well into September. WOW!

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