Transcript Document
Today: Community Ecology • Overview • Brief history • Selective examples • Background for papers Ecological Hierarchy • Organismal ecology = autecology: Evolutionary ecology, Behavior, ecophysiology, morphological adaptations of individuals. • Population: group of conspecific individuals: Population regulation, intraspecific interactions. • Community: multiple species in same area. Interplay of multiple species, interspecific interactions. • Ecosystem: biotic and abiotic factors in a bounded but open system. Energy flow, recycling. • Landscape, Global, Macroecology… Class Poll? Community Ecology is the quintessential study of ecology… It is the proprietary domain of ecologists… (very little sharing or co-option by other sciences or managers) Traditional Ecological Hierarchy • Organismal ecology – strong links to physiology, evolution, systematics… (Endangered Species Act) • Population – strong management implications…Resource management • Community – the how and why of plants, animals and microbes in space and time, and their interactions (biotic and abiotic)…historically, not very “applied” • Ecosystem – Interdisciplinary combining geology, soils, atmospheric studies…also strong management links…Ecosystem services, Ecosystem management… Within vs. Among Trophic Level Approaches… Focus on the biota…. In the Ecological hierarchy, typically mechanistic explanations come from below… Genetics, Ecophysiology, Demography used to explain community patterns… “Hierarchical one-upmanship” = One scientist’s mechanism is another’s pattern…. But – historically, community structure has been ignored in Ecosystem Studies – the black box approach Only recently, have the consequences of altered community composition on ecosystem structure and function been emphasized… Community Ecology Roots are: Pattern Mechanism Observation Theory ---------------------------------------------------------------------------------Focus is on “interactions”…. Ghosts of paradigms past - The degree of interaction among species and populations in communities differentiates the more Holistic perspectives of communities from the more Individualistic perspective (think Clements vs. Gleason). Community: An association of interacting populations, usually defined by the nature of their interaction and the place in which they live. A community is "an assemblage of species populations which occur together in space and time" (Begon, Harper & Townsend). (Community + environment = 'Ecosystem') Most ecologists today are between these two extremes. Largest subdiscipline of Ecology at ESA is community ecology (data source: me!) Interests and domain: Historically: Succession, Niche and niche partitioning, community and diversity patterns, Island biogeography…temporal & spatial aspects of community dynamics… Today: Community assembly rules/restoration ecology Trophic interactions Invasive species Biodiversity and ecosystem stability and function Mechanisms of species coexistence in communities Impacts of species loss….conservation issues Interesting & long history… 1898 - Frederick Clements publishes "The Phytogeography of Nebraska", first American "ecology" book 1899 - Henry Chandler Cowles - studies dune succession and develops “dynamic ecology”, U. of Chicago School 1900-1930 - Clements, with support of the Carnegie Institute publishes numerous volumes on succession, research methods in ecology, phytogeography Early 1900s William Skinner Cooper - a student of Cowles at Chicago, Ph.D. thesis on forests of Isle Royal; studied succession in Glacier Bay; joined University of Minnesota; Rexford Daubenmire was student 1913 - Victor Shelford publishes book on Animal Communities of the Chicago area, Shelford is first president of Ecological Society of America (1915) “Shelford’s law of tolerance” 1926 Henry Allan Gleason - publishes on individualistic hypothesis in ecology 1927 Charles Elton, famous British animal ecologist - refines concepts of ecological niche, proposes negative relationship between diversity and invasion… 1940-78 G.E. Hutchinson - limnologist and zoologist, publishes many influential books and papers, wrote on niche, Ph.D. advisor for Robert MacArthur (Yale School) 1940s-50s John Curtis - developed concept of importance values, strong inductive approaches to vegetation analysis (Wisconsin school) 1956 R.H. Whittaker publishes ordination study of Great Smoky Mountains; becomes major influence in ordination, gradient analysis and succession 1950s- 1960s Robert MacArthur, mathematical/theoretical ecologist, developed island biogeography theory, Ph.D. student of Hutchinson. Thus, major scientists in this subdiscipline of ecology: Historically-F. Clements H. Gleason G.E. Hutchinson E. Lucy Braun (1st female ESA president and award named after her) R. MacArthur R. Whittaker More contemporary--Connell (Intermediate Disturbance Hypothesis) Paine (Food webs and Keystone Species concept) Grime (Species trade-offs and coexistence) Tilman (Resource ratio hypothesis for species coexistence and Biodiversity-Ecosystem function studies) Hubble – Neutral Theory Historically: Strong interest in describing and categorizing communities GRADIENT ANALYSIS (Wisconsin School and Whittaker) Gradient analysis - the portrayal and interpretation of the abundances of species along environmental gradients of physical conditions. Examples of environmental gradients: plants: •soil nitrogen •soil temperature •soil moisture •soil depth •annual precipitation animals: •prey availability •soil texture (for burrowing animals) •height above low tide (for intertidal organisms). Classification and Ordination: Objective ways to seek trends and patterns in community data. Classification is the allocation of species to groups so that members of the same group share many species in common, and members of different groups share relatively few species. This assumes species can be grouped into relatively distinct groups (communities have abrupt boundaries). Ordination is an alternative approach to analysis and is based on the idea that the environment, and therefore species composition, changes gradually, rather than abruptly. Ordination describe gradients in species composition and often relate these to known or suspected environmental gradients. Ordination of plant communities of the Jackson Purchase Region of Kentucky: A. Bottomland Hardwoods; B. Swamps; C1. Flatwoods-Wet Phase; C2. Flatwoods-Dry Phase; D. OakHickory (Open or Savanna-Like); E. Oak-Hickory (White Oak and/or Black Oak); F. Mixed Mesophytic; G. Transitional (disturbed or successional); H. Former Barrens. The purpose of ordination is to assist one in uncovering pattern in data sets that are otherwise too complicated to interpret. Ordination should identify the most important dimensions in a data set, and minimize the "noise", in order to show these patterns. However, ordination techniques are meant primarily as exploratory tools,not for testing hypotheses. Concepts of Community Ecologists: CENTRAL CONCEPT Niche: An organism’s place in the community and what environmental factors limit it to that space (Grinnell) – environmental emphasis An organism's role in its community (Elton) – species emphasis An organism's "ecological position in the world" (Vandermeer 1972). Today: environmental requirements for species as well as the impact of a species on other organisms in the community (Leibold 1995 Ecology) Fundamental vs. realized niche… As always seems to be the case… Despite its strong synthetic role and its crucial importance in community theory, the niche concept remains unclear: "most [ecologists] would agree that niche is a central concept of ecology, even though we do not know exactly what it means" (Real and Levin 1991). The word niche is a “pseudocognate”. A pseudocognate is a term in which each individual who uses it feels that all readers share his/her own intuitive definition, but in reality each individual has their own distinct definition. A long running major interest: explaining why so many species co-exist and patterns of species diversity Many concepts based on the Equilibrium paradigm… Gause – competitive exclusion principle - two species cannot coexist if they share the same resource (Gause 1934) resource partitioning… Hutchinson – niche (multi-dimensional) can be defined and quantified Principle of limiting similarity -how different do the niches of two species have to be in order for them to coexist? (1.3 ratio?) niche partitioning… Today -Functional trait approach – traits that are easily measured and highly informative regarding ecological and life-history strategies. Plant examples: seed size vs. number, Specific leaf area (area/mass)… Can two species co-exist if they occupy the same niche? Stoichiometric axes….and homoeostasis… Experimental addition of N & P to calculate H Yu et al. 2010 Ecology Letters H over time (27 years) H over space (2700 km) Equilibrium paradigm MacArthur & Wilson – Species area and island biogeography Paine – Keystone species Tilman – Resource ratio hypothesis Non-equilibrium components creep in… Connell – Disturbance regimes Ricklefs – Regional vs. local processes and history Keystone species concept Keystone species is one whose impacts on its community or ecosystem are large and greater than would be expected from its relative abundance or total biomass In contrast, dominant species (foundational species)- trees, giant kelp, prairie grasses, and reef-building corals all have impacts that are large but not disproportionate to their total biomass, and therefore they are not keystone species Keystone species can reduce or increase diversity Problem with concept: Difficult to quantify Few actual comparative studies Concept important because it convinced managers and conservationists alike that the ecological impact of single species matters. To manage, understand, and restore ecological assemblages, the roles of individual species have to be understood and considered Thursday Discussion: Hutchinson – conceptual and reflective Ricklefs – regional perspective Hairston et al. – one big idea – Why is the world green? But first – Finish lecture…a bit more of the world of community ecology according to me… And then the story of Joe Wright… Species co-existence: SPECIES-AREA RELATIONSHIPS One of the most fundamental ecological relationships is that as the area of a region increases, so does the number of different species encountered Simply put, the number of species increases with area (not exactly astounding!). But, a less obvious insight occurred later: the increase in species occurs at a decreasing rate Important issue for conservation: the loss of species numbers occurs at an increasing rate as area gets smaller… “z” (the slope of increase or decrease) can vary by taxa and by site Link to Island Biogeography Island Biogeography MacArthur and Wilson proposed the "equilibrium model of island biogeography" in the 1960s. The basic idea of the model is that the number of species on an island is determined by the immigration of new species and the extinction of species already present; when these two rates balance one another, the species number is at equilibrium Single island Extinction rate greater Large vs. small Immigration rate reduced Near vs. far Testing Island Biogeography Theory – Whole Island “species removal” experiments Community saturation experiments Conservation issues – Can reserves be viewed as islands? Many small vs. few large issues? Connectivity and meta-populations Many factors influencing community composition and key community processes….and many other issues in community ecology Trophic interactions (Top down – bottom up control, food webs) J.H. Brown, Univ. New Mexico J.L. Maron, Univ. California What is the most fundamental question being pondered by community ecologists today? Ecosystem function Do species matter and how do they matter? Species number S. Joseph Wright Community Ecologist: The Dream Job Research Biologist Smithsonian Tropical Research Institute APO AA 34002-0938, United States or Apdo 2072, Balboa, Republic of Presenting Team: Panama Jeremy Sueltenfuss Gloria Summay Chris Davis Ecology 505 Dave Gebben Hutchinson – conceptual and reflective Ricklefs – regional perspective Hairston et al. – one big idea – Why is the world green? General comments? What did you like? What did you find a waste of time? Why are these papers considered “Classics”? Impact – Hutchinson (1959) - cited 1518 times, 29/yr…93 times in 2010 already! Hairston et al (1960) – cited 1325 times, 26/yr… 53 times in 2010. Ricklefs (1987)- cited 784 times, 33/yr…31 times in 2010. Hutchinson Hairston et al. Why do they have such an impact? Hutchinson: Why are there so many species of animals? • Trophic argument – complexity (diversity) leads to stability (?) • Heterogeneity of terrestrial habitats – leads to greater diversity (because heterogeneity can be greater at small scale, small animals are the most diverse…) His long drawn out account of the story of Santa Rosalia conjured up images of an old man spinning tales in front of a fireplace to a less than attentive crown of grandkids. Not usually an image I have reading more contemporary articles. Oncequestions, Hutchinson got into the importance meat of his Fundamental unresolved issues, of scale storytelling (about 3 pages in) it became a bit more Predictions that can be tested broadly…. interesting. Hairston et al…. Trophic Interactions and conflicting evidence Top-down regulation Predator controlling herbivore controlling plants Bottom-up regulation Energy/nutrients limiting plants limiting herbivores limiting predators Why is the world green?model -- predators Hairston regulate herbivores (as indicated by downward solid arrows), but herbivores have relatively little effect on plant abundance (as indicated by dashed lines). • Green biomass accumulates in mature terrestrial ecosystems because predators keep herbivores in check. • Predictions regarding the strength of competitive interactions are also made… Addresses a polarized issue…. Predictions that can be tested broadly… Still generating research today… Ricklefs 1987 “…ecological investigations are largely founded on the premise that local diversity… is the deterministic outcome of local processes within the biological community” “Ecologists have ignored history because it was impractical to do otherwise. “Ecologists must accept the possibility of communities in transition between equilibria; the equilibria may have been shifted by changes in climate….” “Conceivably, the equilibrium…may shift much more rapidly than the community can approach it.” Perhaps it has high impact because of the number of provocative statements… I really liked the Ricklefs article and his view that regionalhistorical viewpoint should be included in ecological studies. Hutchinson's paper annoys me…He drones on endlessly… HSS In a staccato note, the authors assumed the best defense is a good offense and peppered their arguments with preemptive idealogical strikes ( e.g., "the logic used is not easily refuted“) Ricklefs I found Ricklefs article the most interesting I very much enjoyed all 3 papers this week, despite the fact that they were mainly what you would call "armchair ecology". As I read the articles I was struck not so much by the science, but instead by the lack of data that was used to write the papers. It appears that all that was needed was a good idea, a good grasp of the written word and you were off to publishing papers. …a useful, if somewhat long-winded, description of the various mechanisms through which top-down controls on populations are thought to occur. Typical of American Naturalist, there is little actual data… Like so many of the older papers we've discussed, Hutchinson overreaches by relying on logical deduction in the absence of sufficient observational or experimental evidence. Given the enormous complexity of ecological systems, it is unlikely that any simple set of premises can be relied upon without frequent verification, because Perhaps this is why they are cited so much?!?! Should we be publishing more on ideas and be less fixed on data? Hairston (1960): This article provides definitive conclusions from the authors about the factors that mediate populations. However, these conclusions are provided without an ounce of scientific evidence and barely even a citation. We know ecological systems are complex….and we know its really, really, really hard to experiment with, and study systems that are very complex. Are we are drawn to logical statements/concepts/idea that appeal to underlying simplicity and structure?…Particularly if those ideas are amenable to verification or falsification via experiments or by testing predictions? Is this a valuable way to make progress in ecology? It’s amazing how some passionately written ideas can later turn to be invalid, criticized and rejected. I think I will be very careful in concluding the results of my own research, lest I become one of those mistaken examples when this decade becomes history to future ecologists but I am afraid if everybody does so then we will never have