Biological Themes Recurring in Ecology and Evolution: (Campbell: Chapter 1)

 Ecology and Evolution:

Aristotle (384-322 B.C.) can be viewed as the first "ecologist". Aristotle's ideas dominated western thinking about the natural world, and their widespread acceptance inhibited development of both ecological and evolutionary thinking for 2000 years. Four postulates in particular were not seriously challenged until the 18th, 19th and 20th centuries:

 Acceptance of the Aristotle's first three postulates was sufficient to inhibit development of evolutionary thinking before the late 17th century, while acceptance of the fourth postulate effectively prevented development of modern ecological thinking before the 20th century. Belief in the balance of nature meant that even late 19th century ecologists were concerned mainly with static patterns, rather than with fundamental processes.

Aristotle's ideas became increasingly unsatisfactory beginning with the 15th century voyages of exploration that eventually forced Europeans to reconsider many ideas:

By the late 17th century, many Aristotilean assumptions were being undermined, and European scholars were primed for a revolution in thinking. The final trigger was probably the Industrial Revolution, which demonstrated that, well within human lifespans, all aspects of the natural world could be altered drastically, without invoking divine intervention. A few key contributors were:

None of these people would have understood the distinction between what we call ecology and evolution today: they thought about both simultaneously. The fields were not clearly separated until after Louis Pasteur showed experimentally in the late 1800s that microbes did NOT generate spontaneously, and Gregor Mendel's work on inheritance became known at the turn of the 20th century, providing the basis of modern genetics. Nevertheless, Ernst Haeckel (1879) had already coined the term "oekologie" as a non-evolutionary concept, to describe studies of interactions between living organisms and their environments.

1. Linear Hierarchies: (standard for most textbooks)

2. Dichotomous Hierarchies: (standard late 20^th century view)

Ecology is inherently interdisciplinary; it is concerned with syntheses among most branches of biology, as well as with many other sciences (e.g. geology, meteorology, oceanography, physics, chemistry…); it deals with complex questions spanning many spatial and temporal scales.

ECOLOGY (Campbell: Chap. 46)

1. Scientific Study: In practice, two general methods are used in ecology, but the second is preferred wherever possible:

Both methods can use one or more of four approaches:

B. Interactions: Modern ecology is concerned with understanding Processes rather than with describing Patterns. It deals with changes in space and time.

C. Organisms: Ecology is concerned mainly with whole organisms as individuals, and as groups of individuals (i.e. populations, communities and ecosystems)

D. Environment: In ecology, environment refers to all factors external to the organisms being studied:

Originally the concept of environment was applied equally to individuals, populations, communities and sometimes even to ecosystems. The modern concept, dating from Andrewartha and Birch (1954), is that only an individual has an environment. This means that all other members of an individual’s own species are considered part of its environment. Andrewartha and Birch also introduced a classification of environmental factors under four general components. This classification has proven extremely useful for organizing ecological studies, and for defining field and experimental protocols. These components are:

Aristotle was recognizably an ecologist who studied nature solely by applying inductive reasoning to a strictly observational approach (e.g. he concluded from external morphology and seasonality that stalked barnacles were juvenile geese!). Because his postulates were the basis of ecological thinking for nearly 2500 years, they also delayed development of modern ecological thinking well into the 20th century. Belief in the balance of nature meant that ecologists tended to emphasize static patterns, rather than recognizing changes as fundamental ecological processes. Aristotlean postulates, especially the balance of nature, persist in popular thinking about ecology and the environment. The "Gaia Hypothesis" is perhaps it's most recent manifestation..

Plant and animal ecology developed along largely independent lines until the 1960s. Plant ecology developed relatively early in the 19th century, with strong biases to wards questions of distributions. Plants are large, easily seen, long-lived, and don't move (as adults). Their limits of distribution are readily detected and mapped. Plant ecology developed first as descriptive "plant sociology" before shifting its emphasis in the 20th century towards physiological studies concerned with identifying the physical or chemical factors limiting those distributions. Hence plant ecology emphasized low density populations in marginal habitats near the physiological limits of tolerance of the species.

Animal ecology developed towards the end of the 19th century, with its primary emphasis on questions of abundance rather than on distributions. This was reasonable, considering that most animals are very difficult to find or catch: they are usually small, highly mobile, often cryptic and secretive, and short lived. Since animals could be found easily only where they were abundant, animal ecology tended to concentrate on high density populations in favorable habitats. In most cases, animals' limits of distribution are unknown and very difficult to determine. By the 1920s, animal ecology was concerned with interactions among species (community ecology) and starting to recognize demography, the study of the structure and growth of populations (Elton, 1927)

Animal and plant ecology began to merge in the 1950s. Andrewartha and Birch (1954) merged the concepts of distribution and abundance by defining the limits of distribution as the place where the abundance falls to zero. In the 1960s, experimental studies of animal distributions became well established; and plant demography (concerned with the structure and abundance of plant populations) became an established discipline by the mid 1970s.

Like many other sciences, ecology diverged during the 20th century into many specialized fields (animal, plant, physiological, population, community, ecosystem, behavioral....ecologies) that tended to advance independently of the others. This trend has been reversed over the last 25 years, and the specialties are increasingly drawing on one another to form a synthesis in which each approach is treated more as looking at a different facet of the same phenomena. Similarly, the 20th century saw partitioning of evolution into many distinct disciplines (mendelian, quantitative, population, and molecular genetics; taxonomy and phylogenetics...) that are now coming together again in new syntheses. Finally, the late 19th century divergence between ecology and evolution, cast in concrete by the r spread of Mendelian genetics in the early 20th century, is also disappearing in such fields as "evolutionary ecology" or "ecological evolution".