- Slides: 25
Ecological Restoration (BIO 409) Dr. Mc. Ewan Restoration Theory and Practice
Dynamics & Equilibrium in Ecosystems Ecological energy is expressed over time. Composition shifts – Why? How? Ecological trajectory • • Ecological trajectories Basins of attraction Threshold models Hysteresis models Successional models Alternative stable states Biotic feedbacks Resilience
F. E. Clements was, during his prime, the most influential ecologist in the world. During ten year periods at the University of Nebraska and University of Minnesota he developed and refined theory for which he is best known: ecological succession. The notion that community systems might go through a dynamic and orderly (and almost organic) set of stages leading to a stable assemblage of species known as the climax was the first attempt at a universal understanding within ecology, and proved an irresistible unifying force among its workers even as an increasing number of studies demonstrated various limitations to theory. Clements left academia in 1917 to join the staff of the Carnegie Institution of Washington as a research associate; from this point on he moved in an increasingly Neo. Lamarckian direction, including attempting to demonstrate that acquired traits could be passed on to descendants. This work isolated him from the mainstream (and ended up unsubstantiable), but it did provide a target for workers involved in the Neo-Darwinian synthesis. The Biographical Dictionary of American and Canadian Naturalists and Environmentalists (1997), p. 157, succinctly lists Clements' major contributions as "development of formal theoretical framework for plant ecology, creation of system of ecological nomenclature, introduction of quantitative methods to the study of vegetation, " and "extensive field research in plant ecology. " http: //people. wku. edu/charles. smith/chronob/CLEM 1874. htm
F. E. Clements Put forth the idea that ecosystems arrive, ultimately, at a stable composition/structure, that is dictated by climate. The “Climatic Climax” community. When to exhaustive lengths describing the orderly phases ecosystems move through prior to arrival at the climax. Was influenced by vegetation zonation, where if you at a certain elevation and aspect you see the same vegetation type over, and over, again across the landscape. This idea is a predecessor to the idea of “Equilibrium Communities. ” A more nuanced idea, to be sure, because it implies “balance” but, still emphasizes a deterministic process leading to a stability http: //people. wku. edu/charles. smith/chronob/CLEM 1874. htm
1 & 2 are “equilibrium concepts. ” In number one the systems is passing through an orderly series of stages arriving at a common endpoint (box D) after that point the system does not change. In two, the system is a bit less orderly, but still arrives at a stable endpoint. Another way to think about equilibrium is a ball and cup model.
Christensen and Peet (1984) provided some evidence to support convergence. They measured forests of a variety of ages across North Carolina and found that they were converging on a endpoint condition. Journal of Ecology Vol. 72, No. 1 (Mar. , 1984), pp. 25 -36 Published by: British Ecological Society http: //www. jstor. org/stable/2260004
Most of eastern North America has been heavily disturbed, but the disturbance was NOT uniform. Some sites were burned 5 times, cut over, and then farmed, and then returned to forest. Some were cut only once. Some were only burned. Etc. Yet, we see really similar forests across a broad range… Equilibrium forces at work?
Manipulating ecosystem dynamics is an essential part of ecological restoration. In many cases, you start from a system that is complete disarrayequilibrium forces are what you need to manage to drive the system toward the desired state. But, what if the system has multipleequilbria?
Manipulating ecosystem dynamics is an essential part of ecological restoration. In many cases, you start from a system that is complete disarrayequilibrium forces are what you need to manage to drive the system toward the desired state. But, what if the system has multipleequilbria as demonstrated in 4 (or in a ball and cup diagram)?
Manipulating ecosystem dynamics is an essential part of ecological restoration. In many cases, you start from a system that is complete disarrayequilibrium forces are what you need to manage to drive the system toward the desired state. But, what if the system has multipleequilbria as demonstrated in 4 (or in a ball and cup diagram)? Or, what if the system had no equilibrium! This is demonstrated in 3, (or via a ball and cup diagram)
Manipulating ecosystem dynamics is an essential part of ecological restoration. In many cases, you start from a system that is complete disarrayequilibrium forces are what you need to manage to drive the system toward the desired state. But, what if the system has multipleequilibria… OR, what if it has settled into a new equilibrium and there is not a clear path back…
In fact, the idea of a climax community and equilibrium conditions has been all but annihilated in the ecological literature. Clements has been over-simplified and is now something of a joke. As an ecologist it is a bit embarrassing to be caught in something that smacks of being Clementsian! Many have put forth the idea that ALL ecosystems are disequilibrium communities. There are no stable enpoints, and things are constantly changing. This is particularly prevalent among paleoecologists who point out that ecosystem drivers are in constant flux. Climate and anthropogenic processes have been dynamic for 15, 000 years in eastern North America and ecosystems are constantly reacting to them. [As an aside, the guy founded ESA and invented the quadrat!! His contributions are enormous…he just got a bit carried away and it has cost his reputation. I think this is a bit like Freud who is sort of a joke now for being wrong so often, but don’t forget Freud more-orless invented the whole idea of psychoanalysis!! The idea that past events can shape current problems and that some of this can be worked through by talking through issues. Before Freud the best idea for someone disturbed was electrocution or sticking a knife up the nose into the brain…hmmmmm] Nevertheless, there are some real distinct patterns (forces) that restorationists have to deal with. Ecosystems near Dayton pretty much want to turn into hardwood forest… for instance.
Transient Dynamics…restorationists must grappled with this!
Concept review. Keystone Species
Keystone. . .
Concept review. Keystone species have a disproportionately large influence on ecosystem structure and function. Remove the species, the whole ecosystem can change Management/Restoration of keystone species (particularly predators) is often an important goal of restoration.
Concept review. Umbrella species are those that have habitat requirements such that managing for that species will de facto protect a much broader suite of species. This is also called a “spillover effect” (see Box 5. 1 in Falk et al) Mussels are the classic umbrella species in our part of the world. Require cold, clean, streams…not a lot of those left http: //fw. ky. gov/pdf/t&ebook. pdf A tiny fraction of federal funds goes to species such as mussels, or plants or insects, or obscure animals. Most funding to charismatic megafauna
Concept review. Flagship species are those that are especially inspirational, thus stand as a representative of a particular ecosystem. These species may be ancillary from an ecological perspective, but they draw attention to the system.
Regional Processes Filter 1) Composition of the species pool and what is the mechanism of species moving into local ecosystems? -lottery model = “more tickets better chance” but still random. -core & satellite = bimodal, many dominant some rare. 2) Dispersal and colonization processes. -priority effects
Local Environmental Filter Restoration relies on creating environmental conditions sufficient to maintain/perpetuate the species assembly desired in the restoration target community. -Abiotic conditions: light levels, soil p. H, water availability, in wetlands hydroperiod; in streams, things like depth and sinuosity. One of the first goals in restoration is to create the appropriate environmental template. -Disturbance regimes: fire, flooding, grazing and other perturbations are critical to the maintenance of some ecosystems. These non-equilibrium processes can reduce competition and create appropriate environmental conditions for restoration success (eg, create exposed soil for seed germination). Can also have a major influence on ecosystem processes. -Habitat complexity: In many cases, restoration seeks to restore some degree of environmental/habitat complexity to systems that have been simplified. Adding sinuosity to streams is an example.
Biotic Filter Abiotic processes, mutualism, competition, etc. , are important in regulating ecological community structure and function. Restorationists must understand (and often manipulate) these processes. -Competition: i) Resource competition. ii) Top-down vs. Bottom-up processes. iii) Invasive species have “changed the game” in many systems. -Food-web/Trophic interactions: Need to understand how target species may be interacting or depending upon other organisms. Will discuss this later in detail (chapter 8) -Mutualism: Grossly underappreciated. Could “make or break” a restoration activity.