Flow chart of Alfalfa Pollination Model

This flow chart helps conceptualize what is happening in alfalfa seed production as a system. It’s not important that you understand all the details; just some important points.

The model consists of two components, the flower pollination component and the bee offspring component. Basically what happens is that a bee population is introduced, flowers are pollinated for some period of time, bees produce offspring, and the result is a seed yield and a bee yield for the next season.

In the flower component, buds come into bloom as open flowers, i.e., the “standing crop” of open flowers, what is available to the bees at a given point in time. If not pollinated within about a week, flowers wilt and leave the system. When flowers are tripped they are also removed from the pool of open flowers, and quickly begin to develop pods, from which we can calculate a seed yield. The rate of flower visitation depends on the number of bees that have been introduced to the field, and the search and handling time of individual bees and some other factors affecting the bees.

In turn, the number of flowers visited by the bees determines how much pollen and nectar they collect which determines how many offspring they make.

Note the feedback loop connecting pods and buds. This is an exponential decline in rate of bud opening as pollination increases. This is consistent with a source-sink model for flower development, where the sink shifts from raceme production to pod development as flowers are pollinated. The exponential decline is also consistent with a phytohormonal model of the influence of mature fruits on new flower and fruit development. A decline in bud opening as fruits increase is a common phenomenon in flowering plants.

Rate of movement into the "open flower" stock depends on pollination. The rates at which flowers move out of the standing crop pool, either to become pods, or not, also depends on pollination because of the difference in longevity of tripped and untripped flowers. This phenomenon may be uncommon among flowering plants, but it has not often been studied.

Top of page

For further information:

Strickler, K. 1996 Seed and bee yields as a function of forager populations: alfalfa pollination as a model system. J. Kansas Entomol. Soc., 69(4) suppl.: 201-215.

Strickler, K. 1997. Flower production and pollination in Medicago sativa L. Grown for seed: model and monitoring studies. In, K.W. Richards, ed. Proc. Int’l Symp. on Pollination Acta Horticulturae 437, ISHS pp. 109-113.

Strickler, K. 2005.  Envisioning Alfalfa Pollination - Let's Move from Color to HDTV to Maximize Yields. Forage Seed News, 12 (1):14-20

Strickler, K. 2007.  Exploring Alternate Conceptions of Flowering Phenology with an Interactive Systems Model.  In. Gardener, C.A.C., M.A.Harris, R.W. Hellmich, H.T. Horner, J.D. Nason, R.G. Palmer, J.J. Tabke, R.W. Thornburg, and M.P. Widrlechner, eds. 9th International Pollination Symposium on Plant-Pollinator Relationships - Diversity in Action: Program and Abstracts.  Iowa State University, Ames, IA, USA  212pp.  
Open the poster (3.5Mbytes; this may be slow.  Requires MSPowerpoint)

New!  The model can now be run on the web.  You don't need a demo or runtime copy from isee systems. 
    Standard version with feedback between fruit development and rate of bloom.
    Modified version with NO feedback between fruit development and rate of bloom (not currently available).
    Advanced version, more realistic features.  Look at this after you are familiar with the first version. 

If you prefer, you can download a free demo copy of isee Player  from isee Systems, and download the model to your computer.   This version contains features that are not supported on the web.

 Right mouse click the hyperlink below  and select "save target as..." :
    Standard version with feedback between fruit development and rate of bloom.
    Modified version with NO feedback between fruit development and rate of bloom.
    Advanced version, more realistic features.  Look at this after you are familiar with the first two versions. 
After downloading, extract the files to run the program with isee Player.

Note copyright.  You are welcome to examine the model.  Contact me for a copy of the model(s) on disk, and for permission to use this model for classroom or research purposes.

Why systems thinking involves a paradigm shift from isee Systems.