Your Turn : Ecology Lab

1. Your Turn: Ecology Lab You tell me. What is your “Dream Ecology Lab”?

2. Writing. Justifying. Proving. • “More people will die as a result of pollution unleashed by Israel’s bombing of the Palestine than perished in the 24 days of war.” • “there will be population emigration. The human population shifts result in deforestation by cutting or fire, draining of wetlands, nutrient depletion and severe.” • “Refugees frequently come into conflict with wildlife and eventually cause their extinction.”

3. Beware… • Hmm… “Air strikes and ground fighting directly impact on wildlife and human populations. For strategic reasons, warfare often takes place in mountain, river and forest regions, where there are high concentrations of wildlife. The noise and disruption, results in the wildlife migrating to neighboring areas or perishing in the now inhospitable environment.” • Plagiarism. (http://www.informaction.org/cgi-bin/gPage.pl?menu=menua.txt&main=weapons_intro.txt&s=War%20%26%20Weapons)

4. Finishing Chapter 21..

5. Why do larger areas have more species? • Larger areas have greater habitat heterogeneity. • For islands, size per se makes the island a better target for potential immigrants from the mainland. • Larger islands support larger populations, which persist because they have: • greater genetic diversity • broader distributions over habitats • numbers large enough to prevent stochastic extinction

6. Diversity Indices • Although species richness is a useful measure of biological diversity, it also has certain problems: • the number of species encountered varies with the number of individuals inventoried • species differ in abundance and thus in their functional roles in communities • Diversity indices have addressed the second of these problems by weighting species by their relative abundance...

7. Summary 1 • A biological community is an association of interacting species. • Ecologists consider community diversity and organization of species into guilds and food webs. • Two competing concepts of community organization are holistic and individualistic, predicting closed and open communities, respectively.

8. Summary 2 • In general, ecologists find that communities do not form discrete units. Species tend to distribute themselves independently along environmental gradients in a pattern more consistent with the open community concept. • Ecologists have devised techniques of gradient analysis to study distributions of species with respect to gradients of environmental conditions.

9. Summary 3 • Community structure can be summarized by means of food webs that emphasize various relationships among species. • Consumers can depress abundances in trophic levels below them in a trophic cascade or top-down effect. Bottom-up effects occur when one trophic level affects productivity of higher trophic levels.

10. Summary 4 • In any community, some species are common and some are rare. Patterns of relative abundance have been characterized, but their meanings are poorly understood. • The number of species increases with the area sampled, more strongly so on islands. • Various indices of diversity have been used to compare the number and relative abundances of species between communities.

11. Chapter 22: Community Development

12. A New Beginning • The island of Krakatau in Indonesia exploded on August 27, 1883, destroying all life: • ecologists have found the island to be an exceptional laboratory for studying the development of biological communities on a raw terrain of volcanic ash

13. Succession • the first plants to arrive were sea-dispersed species • other pioneers were wind-dispersed • by the 1920s, forests had developed on the island • birds and bats were soon attracted to forest habitats, eventually bringing seeds of animal-dispersed trees and shrubs • Figure 22.2

14. Communities exist in continuous flux. • Communities are continually in flux: • much of this flux involves dynamics of existing populations and the flux of energy and cycling of materials: • the appearance and composition of the community itself does not change over time • Following a disturbance, the community rebuilds, eventually attaining its former structure and composition.

15. Southern Poland: (a) after clearing; (b) 7; (c ) 15; (d) 30; (e) 95; (f) 150 yrs • Figure 22.3

16. What is succession? • Succession is the sequence of changes initiated by disturbance. • Or the ‘orderly process of change over time in a community’ • What is a community? • Sequence of appearance and disappearance of species • The ultimate association of species achieved is called the climax community. • F.E. Clements pioneered studies of succession: • subsequent studies have emphasized: • processes that underlie successional change • adaptations of organisms to changing conditions • interactions between colonists and species replacing them

17. successional change. • Any new habitat provides a home for a host of pioneer species: • these colonizers change the environment: • environmental changes may favor later successional species at the expense of the pioneers • the character of the community changes through time • The series of successional stages, or sere, has been observed in the Piedmont of North Carolina: • a sere of agricultural fields to climax hardwood forest

18. Several seres may lead to the same climax. • In Indiana, at the southern end of Lake Michigan, several distinctive seres lead to the climax beech-maple forest: • succession on sand dunes adjacent to Lake Michigan differs markedly from succession on abandoned agricultural fields nearby • succession in marshes, as the wetland fills with sediment, reaches the same climax

19. Primary succession on dunes begins with rhizomatous grasses from the edge (a) &then (b) organic nutrients accumulate; ( c) shrubs (d) trees

20. Some ponds undergo bog succession – (a) behind a beaver dam; (b) stagnant water poor in minerals; (c) gathering detritus…black spruce

21. Primary Succession • Primary succession is the establishment and development of plant communities in newly formed habitats previously lacking plants: • examples include: • sand dunes • lava flows • rock bared by landslides or receding glaciers • one of the best-studied examples of primary succession is the conversion of aquatic habitats to dry land in north temperate and boreal climates...

22. Bog Succession • Retreating glaciers left deep kettlehole ponds where large chunks of ice formed depressions and then melted, initiating bog succession: • rooted aquatic vegetation dominated by sedges extends out from the pond shoreline, forming floating mats • detritus produced by the sedge mat accumulates as organic sediments (peat) on the pond bottom • as a bog accumulates sediment and organic detritus, sphagnum moss and shrubs invade the sedge mat • shrubs are followed by black spruce and larch, which eventually give way to a climax forest of birch, maple and fir on dry land

23. Secondary Succession • Secondary succession occurs when disturbance initiates the regeneration of a climax community: • breaks in a forest canopy are closed as individuals take advantage of new opportunities (light and other resources) • secondary successions may be initiated by a number of different processes: • abandonment of agricultural land • various kinds of wind disturbances, such as hurricanes • fires or disturbances by animals

24. Climax Community • The climax community is the end point of succession: • Clements and others showed that many seres developing under different local environmental conditions progress to the same regional climax: • Clements recognized 14 climaxes in the terrestrial vegetation of North America

25. Rejection of Clements’ Views • More recently, Clements’ notion of the climax as a closed community has been rejected by most ecologists: • ecologists are now inclined to place climax communities in an open continuum within a region: • ecologists in 1930 saw the sugar maple-basswood forest as a regional climax for Wisconsin • today this type of forest is placed within a continuum of many other climax types

26. The Continuum Index • J.T. Curtis and R.P. McIntosh ordered the mature forest communities of southwestern Wisconsin along a continuum index: • this index ranged from dry sites dominated by oak and aspen to moist sites dominated by sugar maple, ironwood, and basswood • the climax vegetation of southwestern Wisconsin is thus a continuum of forest types

27. Succession results in part from changes caused by colonists. • Two factors determine when a species becomes established in a sere, particularly: • how readily it invades newly formed or disturbed habitat: • some plants produce many small seeds, readily carried long distance by wind or animals • other plants germinate or sprout from roots after a fire • how it responds to changes in the environment: • successional species modify the environment in ways that affect themselves and potential colonists...

28. Processes Governing the Course of Succession • Joseph Connell and Ralph Slatyer classified the diverse array of processes governing the course of succession into three categories of mechanisms: • facilitation • inhibition • tolerance • These mechanisms describe the effects of one species on the probability of establishment of another.

29. Facilitation • Facilitation embodies Clements’ view of a developmental sequence in which each species paves the way for the next: • alder trees (Alnus) harbor nitrogen-fixing bacteria in their roots: • these nitrogen-fixers provide an important source of nitrogen for soils developing on sandbars in rivers and in areas exposed by retreating glaciers

30. Inhibition • Inhibition of one species by the presence of another is a common phenomenon, and this process can be seen in successions: • in subtidal habitats in Australia, bryozoans can prevent the establishment of tunicates and sponges • When inhibition is acting, succession moves forward only through the death and replacement of established individuals: • this results in an inevitable shift toward longer-lived species

31. Tolerance • Through tolerance, a species can invade new habitat and become established independently of the presence or absence of other species: • early colonizers of agricultural fields can tolerate the harsh conditions of newly exposed ground • Under this mechanism: • early stages are dominated by poor competitors with short life cycles • superior competitors constitute the climax species, but grow more slowly and express dominance later

32. Approaching the Climax • Succession continues until the addition of new species and exclusion of established species no longer changes the environment: • at this point succession reaches climax: • the community growth form has come into equilibrium with its physical environment

33. How long do successions last? • The time required to reach climax varies considerably from one system to the next: • in the humid tropics, forests regain most of their species within 100 years of clear-cutting • old field succession to mature oak-hickory forest takes 150 years in North Carolina • the beech-maple climax forest requires up to 1,000 years to develop on Lake Michigan sand dunes

34. Are there predictable patterns in succession? • Communities are typically most diverse and complex at intermediate stages of succession, but ecologists do not know why. • Many other properties of communities change: • the ratio of biomass to productivity increases • the net accumulation of biomass slows and stops • a greater proportion of the nutrients available to the community reside in organic materials • detrital food chains predominate over grazing chains

35. Early and late successional species have different adaptations. • Early and late successional species are characterized by suites of correlated attributes or strategies. • Colonizers: • produce many small seeds • rely on dispersal by wind or become attached to animals • can remain dormant for long periods in seed banks • allocate a relatively large amount of biomass to stems and leaves • grow rapidly to small size • are shade-intolerant

36. Early and late successional species have different adaptations. • Late successional species: • produce few large seeds • rely on dispersal by gravity or are eaten and dispersed by animals • have relatively little dormancy and longevity in the soil • allocate a relatively large amount of biomass to roots and woody stems • grow slowly to large size • are shade-tolerant

37. Some climax communities are maintained by extreme conditions. • Grazing or periodic fires can determine the composition of climax communities: • along the Gulf and Atlantic coasts of the United States, pine forests are maintained by periodic fires: • longleaf pines and associated species have life cycles and many strategies that ensure their persistence in frequently-burned ecosystems • fires are essential to maintenance of the longleaf pine ecosystem through effects that include suppression of scrub oaks and other woody broad-leaved species • chaparral and prairie are other fire climaxes

38. Transient Climaxes • Not all climaxes persist. Transient climaxes include: • development of plant and animal communities of small ponds or depressions that dry up in summer or freeze solid in winter: • the communities established are destroyed each year • each spring the ponds or depressions are restocked by immigrants or dormant propagules, renewing the succession • successions of microorganisms and scavenging animals on excreta or dead plants and animals (no climax!)

39. Cyclic Climaxes • In simple communities, the particular life history characteristics of a few dominant species can create a cyclic climax: • for example, when species A can germinate only under species B, B only under C, and C only under A: • a regular cycle of dominance in the order A, C, B, A, C, B, A will ensue • the length of each stage is determined by the life span of each species • wind or frost heaving often drive such cycles

40. Cyclic Climaxes: Examples • There are numerous examples of cyclic climaxes: • waves of wind damage and regeneration in subalpine balsam-fir forests in eastern North America • cycles of damage and regeneration in dwarf heath communities in northern Scotland • cycles of hummocks and hollows in windy regions where hummocks build around clumps of grass • shifting successional mosaics associated with treefall gaps in many forested ecosystems

41. Summary 1 • Succession is community change following either habitat disturbance (secondary succession) or the exposure of new substrate (primary succession). • The initial stages of a successional sere depend on the intensity and extent of disturbance. The end-point (climax) is determined by climate and topography.

42. Summary 2 • Early successional species tend to be good colonizers and grow rapidly; later successional species tolerate low resource levels and dominate direct interactions with other species. • Connell and Slatyer classified successional processes into facilitation, inhibition, and tolerance.

43. Summary 3 • Succession continues until the community becomes self-perpetuating in climax. • Trends apparent in many successions include the accumulation of biomass, but diversity peaks in intermediate stages. • The nature of the climax is profoundly affected by local conditions, including fire and grazing. • Climaxes may also be transient or cyclic in nature.