LIFE HISTORIES
All organisms have a life history strategy. For plants you must take multiple factors when assessing life histories. Knowing a species life span (perennial or annual), capability for dormancy, and frequency of reproduction is crucial for understanding its life history. On this page we will go over these factors that shape an organisms life history.
life span
There are two main classifications of life-span—annuals and perennials. Annuals are what they sound like, they go through all of their life stages, from seed to reproductive to death, in the course of one year. Perennials are the opposite of that, they take many years to go through their entire life stages. Two really extreme examples of contrasting life spans are the Bristlecone Pines, which can live upwards of 5,000 to 7,000 years old and the Mariposa Clarkia which goes from seed to flowering to death in nine months. One intermediate example is the Clay Mariposa Lily which can live for several decades.
Bristlecone Pine
Image by MNN
Clay Mariposa Lily
Image by Tatyana Soto
Mariposa Clarkia
Image by Keir Morse
Dormancy
Every seed has a capacity for dormancy, but the amount of time spent dormant varies wildly for every species. After the seed is developed it enters a period of dormancy to prevent germination on the parent plant. Typically, the seed will refrain from germinating until the following season, for example a seed will remain dormant from July until the start of the rainy season. If the seed does not germinate shortly after it is dispersed it enters a new stage of dormancy where it could remain for weeks, years, and even centuries! However, dormancy is not a perfect escape route. Seeds that lay dormant for an extended period of time risk the chance of being destroyed by human and animal traffic or becoming buried so deep they can never reach the surface to germinate. A seed will germinate when environmental conditions are favorable, water is necessary for germination but many species require fire, freezing, or an exact amount of sunlight in a day to germinate.
Frequency of Reproduction
Reproduction is extremely taxing and costly for an organism, so balancing the benefits and costs over ones lifetime is important. Annual species reproduce at the very end of their life span and they produce many offspring during that one reproduction event, this is called semelparity. Annual species typically have a high capacity for dormancy because an individual has that one shot at passing on their genes. If all of the plants seeds germinate in unfavorable conditions they will not survive and the cost of reproduction would have been for nothing. So staying dormant until conditions are perfect is really advantageous for short-lived species. For long lived species, they reproduce multiple times over their life, iteroparity, which increases the chance that at least one of their offspring establishes and survives. This influences the capacity for dormancy, since they have that increased chance, their seeds typically do not remain dormant for long and the environment typically remains more stable than the environment annuals live in. There is one last reproductive strategy some species utilize, the Big Bang strategy. Species that live in extremely stressful conditions will take many years, typically hundreds of years, in order to allocate enough resources to reproduce, and then the energy it takes to reproduce kills them once they have done so.
