Forbes & Cowles - Ecology emerging in the late 19th Century

Forbes 1887 – The Lake as a Microcosm

Forbes begins with an introduction in which he makes some general observations about lakes and the animal life found within them. The notion of the sensibility of the complex of life in such environments is emphasized, by which Forbes seems to mean the interaction and interdependence of all the organisms in the local ecosystem, suggesting it is impossible to really understand any individual species without some concept of its place in the community as a whole. He states his purpose of examining the lacustrine life of northern Illinois within the context of this idea, based on his and colleagues’ observations and sampling of watershed lakes in the uplands of northern Illinois. Differences between watershed and fluviatile lakes are described. The latter are characterized by seasonal overflows and fluctuating conditions, with effects cascading through trophic levels and resulting in oscillating population cycles. Forbes considers this one of the best examples of the how the system of organic life can adapt.

Forbes then gives some contextual description for the seven more isolated watershed lakes that are the primary focus of his paper, including a brief mention of the methods of observation used. He goes on to describe the animal life found in these lakes, including the fishes, molluscs, arthropods, and crustaceans (esp. Entomostraca), remarking on their relative abundance and diversity, the habitats within the lakes different life forms occupy, and how these compare to other lakes in the region and in Europe. Forbes then gives several examples of the organic relations among the lacustrine fauna, including the common black bass and all its food prey, competitors, and predators, as well as the bladderwort – a carnivorous plant which apparently competes with fish by feeding upon many of the same crustaceans and insects. These relations are then placed in the evolutionary context of all the species’ struggle for existence against one another and the severe conditions this creates. But in spite of this, Forbes emphasizes that natural selection in fact promotes a community of interest even among species with seemingly antagonistic relationships due the interdependence and food relationships in the community. He concludes by remarking on the apparent contradiction that exist in natural systems, where organisms that are seemingly hostile or indifferent to one another produce cruel conditions, but conditions that nonetheless appear to promote life and a balanced harmonious equilibrium.

Kingsland’s introduction describes Forbes as being influenced by both Darwinian evolutionary biology, and by the Victorian natural history idea that natural systems tends to be stable and self-regulating (articulated by Spencer). The Lake as a Microcosm provides a good synthesis of these ideas, as well an early articulation of the concepts of a biological community and of food webs. I was surprised at the sophistication of the thinking Forbes exhibited in an era when ecology was not yet a formal field of study. Though his methods were different from what would be considered sufficient today - largely qualitative – I found it challenging to identify misconceptions in Forbes’ thinking. Examples could include the notion that aquatic ecosystems are completely isolated and oblivious to their terrestrial counterparts, as well as an overemphasis on equilibrium – population/ecosystem/community dynamics have become major themes in ecology. Here are some additional thoughts and questions to consider:

·         Are there other misconceptions you noticed in The Lake as a Microcosm?

·         Both traditional natural history and evolutionary biology seem to play key roles in the origins of ecology. How does ecology, and Forbes in particular, depart from these earlier fields? In what ways does Forbes’ thinking seem more like natural history, rather than ecology? Is there a place for natural history in ecology today?

·         What are Forbes’ methods and data? Is he justified in making the conclusions he does based on this?

·         Kingsland describes Forbes’ motivations as being both practical (build scientific basis for agriculture) and basic (use theoretical framework of evolutionary biology; pg. 3). What do you think was the stronger motivation in The Lake as a Microcosm? How about in ecology as a whole, both in its early days and today?

Cowles 1899 - The Ecological Relations of the Vegetation on the Sand Dunes of Lake Michigan

Cowles starts by expressing the scientific value of studying plant communities in sand dunes and why sand dunes are an ideal place to learn about ecology. “The sand dunes furnish a favorable region for the pursuit of ecological investigations because of the comparative absence of the perplexing problems arising from previous vegetation.” Essentially the formation of dunes wipes out all pre-existing traces of vegetation thereby creating a clean slate and forcing plants to establish from existing physical conditions.

This papers describes the environment of the sand dunes of Lake Michigan and the ecology of the flora that exist in this habitat. Cowles aims to understand and explain the dynamics of the sand dune phenomena and “uncover the laws which govern the panoramic changes.”  He refers to the sand dune environment as the “dune-complex” where it is a moving landscape – a restless maze always changing. This restless maze advances as a whole in one direction (the direction of prevailing winds) but with individual portions advancing in all directions (small dunes may advance in any direction provided they are protected from winds blowing in other directions).

The main ecological factors influencing floral establishment and persistence:

·         Temperature: In the summers the dunes are hot and sunny where warming begins in early spring and cooling begins in early fall followed by periods of very cold temperatures and severe winds favoring arctic floras.

·        Wind: Wind is the most potent of all factors in determining the character of dune vegetation. The windward sides of the vegetation endure intense sand blasts and are often damaged. Wind is the chief destroyer of plant societies by blowing away soil from underneath exposing roots or by burying vegetation that exists in depressions or low-lying areas with the advancement of dunes impelled by the winds.

·        Soil: The soil is mostly comprised of Quartz sand and is extremely porous lacking nutrition and organic matter.

·        Water:  Overall sand dunes are a very dry environment especially for short root systems and periods of drought favor xerophytic floras.

·        Topography: Sand dune slopes are driest with southern exposures producing more xerophytic flora. Depressions between sand dunes are much wetter and offer the opportunity for humus to accumulate resulting in the presence of different floral species. 

·        Plants and organic matter: Humus can build producing great soil but can also be covered or buried too deeply to be utilized until it is uncovered again someday.

The scanty flora is not due to the lack of water in the soil but to the instability of the soil and to the xerophytic air.

Cowles spends some time discussing plant societies and ecological succession which he terms genetic succession – “….arrange plant societies in order of development - this order more faithfully expresses genetic relationships than any other.” In the dune-complex the beach is the most extreme environment with conditions for plant life becoming less and less severe as they pass through several stages before culminating in the normal climax type of the lake region which is the more genial deciduous mesophytic forest.

Also present in the dynamics of the dune-complex is what Cowles terms Rejuvenation. Rejuvenation is when an established dune has its vegetation destroyed and passes into a state of activity (succession). Rejuvenation most commonly takes place as a result of a wind sweep and the majority of rejuvenated dunes are developed from established coniferous dunes that exist in the windward slopes near the lake. Plants do not succeed in stopping the movement of a dune, only a decrease in wind energy resulting from increased distance from the lake or to barriers can do so. 

In conclusion the sand dune environment is not only variable but reaches more than one extreme – water, temperature, and wind resulting in a dynamic succession of plant communities over relatively short periods of time with various plant species that are each adapted to a particular extreme. 

Questions:

·        What ecological principles are being put to the test, or is Cowles hoping to test, by studying the vegetation of sand dunes?

·        What are the main lessons learned or the main contributions that Cowles made to the discipline of ecology with this study?

·        Do you agree that genetic succession is most faithfully expressed by the order of development of plant societies? Is the term genetic succession still used and if so in what context?  Are genetic and ecological succession synonymous?

Overall questions to consider:

                  What are some similarities and differences between Forbes 1887 and Cowles 1899? How does Cowles appear to build on Forbes ideas, and what new concepts does he bring in? Collectively, what do these two pieces say about the emerging field of ecology in the late 19^th Century?

Note: We will discuss these two pieces on Tuesday. Clements and Gleason will be discussed Thursday, with summaries and questions coming in a separate post.