Tuesday, June 11, 2013



Ecology is the branch of science studying the relationships of the physical and biotic features of the environment.  It is primarily the study of what is happening now with organisms in respect to all features of the world around them.  Ecology goes hand in hand with evolution to give us an understanding of the world around us.

Evolution tells us more about the past and helps us understand the present.  Ecology tells us more about the present and helps us understand the past.  Both can use all other branches of science to contribute to the story.  Basics of ecology combined with the concept of natural selection are particularly valuable to understand the long term course of evolution.


The trophic relationships (or role in the food chain) among producers (mostly plants), herbivores, carnivores, and reducers are fundamental.  If you have not studied ecology you can find out about them in a text such as the one by Dr. Richard Brewer (The Science of Ecology, 1991).  You can find out about his book on his website (http://richardbrewer.org/ ).  His blogging there has gone more to applying ecological knowledge to efforts to preserve biotic communities.  His most recent book, Conservancy: The Land Trust Movement in America (2003, Univ. Press of New England, Dartmouth College imprint) is a product of that interest.

“Jobs” of organisms in an ecological sense

The hypothetical “ecological niche”, though not necessarily a reality, is a useful concept to understand the history of evolution of biotic communities.  Following extinction events that greatly reduce the diversity of plant and/or animal communities, we find that vacated niches are refilled rather rapidly in an evolutionary sense.  But different species do the job.  The same principle is involved in marsupials providing the kangaroo and other large herbivores in Australia whereas other temperate to tropical lands have had deer and other large ungulates evolve to do that herbivore job.  

The complete story for an organism involves its physical dimensions and interactions with many other properties of the organism and its environment.  Thus as animals first emerged the early ones lacking circulatory systems had to be either very small or flattened or with most active tissues on the surface or perforated or somehow adapted to get sufficient oxygen to all tissues needing it.  As size increased they needed some means of support.  They did not know that, but those that had variation providing such needs out-competed their unchanged relatives.

Multiple functions as a base for evolution of complexity and/or primary function

Many things have more than one use.  This is an especially useful concept to help understand evolution.  An appendage can be useful for one or more functions such as movement, sensory input, respiration, feeding, defense, and reproduction.  One example; when appendages are duplicated on many segments as on an arthropod, selection can eventually result in specializations that differ on different segments.  The principle is one reason biology classes often illustrate the concept with study of a sequence including a worm, a crayfish, a grasshopper, and one or more vertebrates.

My study of isopods showed me an example of how some changes occurring in embryos were based on shifts in a tissue with multiple uses.  The realization that changes can occur in an embryo that are essentially independent of adult evolution made it easier for me to understand the reason behind blogs where I will try to explain the origin of the deuterostomes from the protostomes at the annelid level.  It was an old theory that had been abandoned due to the great difference in the embryology.  I hope to show how the shift occurred.  The Lophotrochozoa-Ecdysozoa error might not have occurred if I had been able to publicize the concept more effectively years ago.

Joseph G. Engemann     June 11, 2013

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