Insect Ecology - An Ecosystem Approach 2nd ed - Chapter 10 pot

Successional Change in Community Structure Among the major environmental issues facing governments worldwide is theeffect of anthropogenic activities e.g., altered atmospheric or aquatic

10 Community

Dynamics

I Short-Term Change in Community Structure

II Successional Change in Community Structure

Among the major environmental issues facing governments worldwide is theeffect of anthropogenic activities (e.g., altered atmospheric or aquatic chemistry,land use, species redistribution) on the composition of natural communities andthe ecosystem services they provide to humans How might changes in commu-nity structure affect epidemiology of human diseases? How stable is communitystructure, and how sensitive are communities and ecosystems to changes inspecies composition? Our perception of communities as self-organizing entities

or random assemblages has significant implications for our sensitivity to speciesloss and our approach to management of ecosystem resources

As with population dynamics, study of changes in community structurerequires long periods of observation Few studies have continued over sufficientlylong time periods to evaluate many of the factors presumed to affect community

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structure However, paleoecological evidence and studies of community ery following disturbance have provided useful data Research on factors affecting community structure over a range of temporal scales can enhanceunderstanding of the degree of stability in community structure and anticipation

recov-of responses to environmental changes

I SHORT-TERM CHANGE IN COMMUNITY STRUCTURECommunity structure changes over relatively short time periods Short-term vari-ation in community structure reflects interactions among species responding differently to fluctuating abiotic conditions and species interactions Relativelyfew studies measured effects of seasonal or annual changes in arthropod com-munities over extended periods Several studies represent annual to decadaldynamics in arthropod communities

Fluctuating weather conditions and disturbances can cause appreciable changes

in arthropod community structure Changes in precipitation pattern can elicit

dif-ferential responses among arthropod species Schowalter et al (1999) found that

particular arthropod species, as well as the entire arthropod community, associated

with creosotebush, Larrea tridentata, in southern New Mexico showed distinct

trends in abundance over an experimental gradient in precipitation volume dances of several species increased with moisture availability, whereas abundances

Abun-of others declined with moisture availability, and some species showed nonlinear

or nonsignificant responses Multivariate analysis indicated distinct communitystructures on plants subjected to different amounts of precipitation

Polis et al (1997b, 1998) studied community changes on desert islands in the

Gulf of California during a 5-year period (1990–1994), which included an El Niñoevent (1992–1993) Winter 1992 precipitation was 5 times the historic mean andincreased plant cover 10–160-fold Insect abundance doubled in 1992 and 1993,compared to 1991 levels, with a significant shift in dominance from detritivoressupported by marine litter to herbivores supported by increased plant biomass.Spider densities doubled in 1992 in response to prey abundance, but declined in

1993, despite continued high plant and prey abundance, as a result of increasedabundance of parasitoid wasps, partially supported by nectar and pollenresources These changes were consistent among islands throughout the archi-pelago, indicating that general processes connecting productivity and consump-tion governed community dynamics in this system

Changes in precipitation pattern in western Oregon, United States, between

1986 and 1996 altered the relative abundances of dominant folivore and sucker species in conifer canopies (Fig 10.1) In particular, western spruce

sap-budworm, Choristoneura occidentalis; sawflies, Neodiprion abietis; and aphids, Cinara spp., were abundant during a drought period, 1987–1993, but virtually absent during wetter periods A bud moth, Zeiraphera hesperiana, was the domi-

nant folivore during wet years but disappeared during the drought period.Schowalter and Ganio (2003) described changes in arthropod communitystructure in tropical rainforest canopies in Puerto Rico from 1991 to 1999.Hurricane Hugo (1989) created 30–50-m diameter canopy gaps dominated by

early successional shrubs, vines, and Cecropia schreberiana saplings Several

species of scale insects and a phytophagous mirid bug, Itacoris sp., were

signifi-cantly more abundant on foliage in canopy gaps, compared to nongaps, in 1991and again following Hurricane Georges (1998), suggesting positive response tostorm disturbance Scale insect and folivore abundances were significantly moreabundant during a record drought (1994–1995), compared to intervals betweendisturbances, providing further evidence of responses to disturbances

Factors that increase competition or predation can reduce population sizes ofparticular species Some species may become locally extinct, whereas others showpopulation irruptions Changes in species abundances affect interactions withother species Both the strength and direction of interaction can change greatly

Herbivores that have little effect on their hosts at low abundances can interact

in a more predatory manner at high abundances Reduced abundance of onemember of a mutualism can jeopardize the persistence of the other

I SHORT-TERM CHANGE IN COMMUNITY STRUCTURE 285

30 60 100 300

Year

Folivores Sap-suckers Pollen and seed feeders Predators

Fungivores

FIG 10.1 Temporal change in arthropod abundances in old-growth Douglas fir canopies at the H J Andrews Experimental Forest in western Oregon; 1989 and 1996 were relatively wet years; 1992 was in the middle of an extended drought period

(1987–1993) Z., Zeiraphera hesperiana; Ch., Choristoneura occidentalis; N., Neodiprion

abietis; Ci., Cinara spp.; A., Adelges cooleyi; Co., Coccoidea (4 spp.) Note the log scale

of abundance Data from Schowalter (1989, 1995 and unpublished data).

Changes in species composition and abundance alter species diversity, foodweb structure, and functional organization Change in abundance of species atone trophic level can affect the diversity and abundance of species at lowertrophic levels through trophic cascades For example, reduced predator abun-dance usually increases herbivore abundance, thereby decreasing plant abun-dance (Carpenter and Kitchell 1987, 1988, Letourneau and Dyer 1998).

II SUCCESSIONAL CHANGE IN COMMUNITY STRUCTURERelatively predictable changes in community structure occur over periods ofdecades to centuries as a result of succession on newly exposed or disturbed sites.New habitats become available for colonization as a result of tectonic activity,glacial movement, sea level change, and sediment deposition or erosion Speciescolonizing newly exposed surfaces usually are small in stature, tolerant of exposure or able to exploit small shelters, and able to exploit nonorganic orexogenous resources Disturbances to existing communities affect each speciesdifferently, depending on its particular tolerances to disturbance or postdistur-bance conditions (see Chapter 2) Often, legacies from the predisturbance com-munity (such as buried rhizomes, seed banks, woody litter, and animals surviving

in protected stages or microsites) remain following disturbance and influence thetrajectory of community recovery

The process of community development on disturbed or newly exposed sites

is called ecological succession The succession of populations and communities

on disturbed or newly exposed sites has been a unifying concept in ecology sincethe time of Cowles (1911) and Clements (1916) These early ecologists viewedsuccession as analogous to the orderly development of an organism (ontogeny).Succession progressed through a predictable sequence of stages (seres), driven

by biogenic processes, which culminated in a self-perpetuating community (theclimax) determined by climatic conditions Succession is exemplified by thesequential colonization and replacement of species: weedy annual to perennialgrass to forb, to shrub, to shade-intolerant tree, and finally to shade-tolerant treestages on abandoned cropland Succession following fire or other disturbancesshows a similar sequence of stages (Fig 10.2)

Although the succession of species and communities on newly exposed or turbed sites is one of the best-documented phenomena in ecology, the nature ofthe community and mechanisms driving species replacement have been debatedintensely from the beginning Gleason (1917, 1926, 1927) argued that succession

dis-is not directed by autogenic processes but reflects population dynamics of vidual species based on their adaptations to changing environmental conditions.Egler (1954) further argued that succession could proceed along many potentialpathways, depending on initial conditions and initial species pools E Odum(1969) integrated the Clementsian model of succession with ecosystem processes

indi-by proposing that a number of ecosystem properties, including species diversity,primary productivity, biomass, and efficiency of energy and nutrient use, increaseduring succession Drury and Nisbet (1973) viewed succession as a temporal gra-dient in community structure, similar to the spatial gradients discussed in Chapter

9, and argued that species physiological tolerances to environmental conditionswere sufficient to explain species replacement More recently, the importance ofdisturbances and heterotroph activity in determining successional processes andpreventing ascension to the climatic climax has been recognized (e.g., Davidson

1993, MacMahon 1981, Ostfeld et al 1997, Pickett and White 1985, Schowalter

1981, 1985, Willig and Walker 1999)

The concept of succession as goal-oriented toward a climax has succumbed

to various challenges, especially recognition that succession can progress alongvarious pathways to nonclimatic climaxes under different environmental con-ditions (Whittaker 1953) Furthermore, the mechanism of species replacement isnot necessarily facilitation by the replaced community (e.g., Botkin 1981,Connell and Slatyer 1977, H Horn 1981, McIntosh 1981, Peet and Christensen

1980, Whittaker 1953, 1970) Nevertheless, debate continues over the integrity ofthe community, the importance of autogenic factors that influence the pro-cess, and the degree of convergence toward particular community composition

(Bazzaz 1990, Peet and Christensen 1980, Glenn-Lewin et al 1992, West et al.

FIG 10.2 Diagrammatic representation of upland white spruce forest succession

in Alaska following fire From van Cleve and Viereck (1981) with permission from Springer-Verlag Please see extended permission list pg 571.

A Patterns of Succession

Two types of succession can be recognized Primary succession occurs on newly

exposed substrates (e.g., lava flows, uplifted marine deposits, dunes, newlydeposited beaches, etc.) Primary succession usually involves a long period of soil

formation and colonization by species requiring little substrate modification ondary succession occurs on sites where the previous community was disturbed

Sec-and is influenced by remnant substrate Sec-and surviving individuals Although moststudies of succession have dealt with trends in vegetation, heterotrophic succes-sions, including successions dominated by insects or other arthropods, have con-tributed greatly to perspectives on the process Insects and other arthropodsdominate the development of freshwater communities and litter (especiallywoody litter and carrion) communities, and succession in these habitats occursover shorter time scales than does succession involving longer-lived plant species.Succession varies in duration from weeks for communities with little biomass(e.g., carrion feeders) to centuries for communities with abundant biomass (e.g.,forests) Shorter successions are amenable to study by individual researchers.However, forest or desert succession spans decades to centuries and has not beenstudied adequately throughout its duration (see Fig 10.2) Rather, forest succes-sion usually has been studied by selecting plots of different age since disturbance

or abandonment of management to represent various seres (i.e., the quence approach) Although this approach has proved convenient for compar-ing and contrasting various seres, it fails to account for effects of differences

chronose-in chronose-initial conditions on subsequent species colonization and turnover processes

(e.g., Egler 1954, Schowalter et al 1992) Even Clements (1916) noted that

com-parison of the successional stages is less informative than is evaluation of thefactors controlling transitions between stages However, this approach requiresestablishment of long-term plots protected from confounding activities and acommitment by research institutions to continue studies beyond the usual con-fines of individual careers Characterization of succession is a major goal of thenetwork of U.S and International Long Term Ecological Research (LTER) Sites(e.g., Van Cleve and Martin 1991) Long-term and comparative studies willimprove understanding of successional trajectories and their underlying mechanisms

A number of trends have been associated with vegetation succession alists or r-strategists generally dominate early successional stages, whereas spe-cialists or K-strategists dominate later successional stages (Table 10.1, see Fig.10.2) (Boyce 1984, V.K Brown 1984, 1986, Brown and Hyman 1986, Brown and

Gener-Southwood 1983, Grime 1977, Janzen 1977, D Strong et al 1984; see Chapter 5).

Species richness usually increases during early-mid succession but reaches aplateau or declines during late succession (Peet and Christensen 1980, Whittaker1970), a pattern similar to the spatial gradient in species richness across ecotones(Chapter 9)

E Wilson (1969), based in part on data from Simberloff and Wilson (1969),suggested that community organization progresses through four stages: nonin-teractive, interactive, assortative, and evolutionary The noninteractive stage

TABLE 10.1 Life history strategies of insects from different successional stages Updated from V K Brown (1984) by permission from V K Brown

and the American Institute of Biological Sciences, © 1984 American Institute of Biological Sciences.

Mobility (% fully winged species) 94 84 80 79 Heteroptera (V K Brown 1982)

Generation Time (% species >1 generation/yr) 43 50 33 3 Exopterygote herbivores (V K Brown

and Southwood 1983)

41 37 10 12 Heteroptera (V K Brown 1982) Size (mean body length, mm, ±SEM) 3.68 ± 0.57 3.59 ± 0.63 3.86 ± 0.63 4.14 ± 0.67 all insect species (V K Brown 1986)

Reproductive potential (mean number of 70.0 ± 4.4* 50.2 ± 2.0 ** aphids (V K Brown and Llewellyn 1985)

embryos ±SEM)

Niche breadth (scale 1–5; 1 = highly specialized) 3.35 3.10 2.87 1.79 sap feeders (V K Brown and

Southwood 1983) 1.60 1.29 1.33 3.05 weevils (V K Brown and Hyman 1986)

* on herbaceous plants; ** on woody plants

occurs early during succession (first decade), when species richness and tion densities are too low to induce density-dependent competition, predation,

popula-or parasitism As species number increases and densities increase, interactionstrength increases and produces a temporary decline or equilibrium in speciesnumber, as some species are excluded by competition or predation The assorta-tive stage occurs over long disturbance-free time periods as a result of speciespersistence in the community on the basis of efficient resource use and co-existence Niche partitioning allows more species to colonize and persist Finally,co-evolution over very long time periods increases the efficiency of interactionand permits further increase in species number However, most communities are

disturbed before reaching the assortative stage The intermediate disturbance hypothesis predicts that species richness is maximized through intermediate

levels of disturbance that maintain a combination of early and late successionalspecies (Connell 1978, Sousa 1985)

Arthropod communities also change during vegetative succession (see Table10.1) (V K Brown 1984, Shelford 1907, Weygoldt 1969) E Evans (1988) foundthat grasshopper assemblages showed predictable changes following fire in agrassland in Kansas, U.S.A The relative abundance of grass-feeding species ini-tially increased following fire, reflecting increased grass growth, and subsequentlydeclined, as the abundance of forbs increased

Schowalter (1994, 1995), Schowalter and Crossley (1988), and Schowalter andGanio (2003) reported that sap-sucking insects (primarily Homoptera) and antsdominated early successional temperate and tropical forests, whereas folivores,predators, and detritivores dominated later successional forests This trend likelyreflects the abundance of young, succulent tissues with high translocation ratesthat favor sap-suckers and tending ants during early regrowth

V K Brown and Southwood (1983) reported a similar trend toward increasedrepresentation of predators, scavengers, and fungivores in later successionalstages They noted, in addition, that species richness of herbivorous insects andplants were highly correlated during the earliest successional stages but not latersuccessional stages, whereas numbers of insects and host plants were highly correlated at later stages but not the earliest successional stages Brown andSouthwood (1983) suggested that early colonization by herbivorous insectsdepends on plant species composition but that population increases during laterstages depend on the abundance of host plants (see also Chapters 6 and 7)

Punttila et al (1994) reported that the diversity of ant species declined during

forest succession in Finland Most ant species were found in early successionalstages, but only the three species of shade-tolerant ants were common in old(>140-year-old) forests.They noted that forest fragmentation favored species thatrequire open habitat by reducing the number of forest patches with sufficientinterior habitat for more shade-tolerant species

Starzyk and Witkowski (1981) examined the relationship between bark- andwood-feeding insect communities and stages of oak-hornbeam forest succession.They found the highest species richness in older forest (>70 years old) with abun-dant dead wood and in recent clearcuts with freshly cut stumps Densities ofmining larvae also were highest in the older forest and intermediate in the recentclearcut Intermediate stages of forest succession supported fewer species and

lower densities of bark- and wood-feeding insects These trends reflected thedecomposition of woody residues remaining during early stages and the accu-mulation of woody debris again during later stages.

Torres (1992) reported that a sequence of Lepidoptera species reached outbreak levels on a corresponding sequence of early successional plant speciesduring the first 6 months following Hurricane Hugo (1989) in Puerto Rico but disappeared after depleting their resources Schowalter (unpublished data) observed this process repeated following Hurricane Georges (1998)

Davidson (1993), Schowalter (1981), and Schowalter and Lowman (1999) gested that insect outbreaks and other animal activity advance, retard, or reversesuccession by affecting plant replacement by nonhost plants (see later in thischapter)

sug-Heterotrophic successions have been studied in decomposing wood, animalcarcasses, and aquatic ecosystems These processes can be divided into distinctstages characterized by relatively discrete heterotrophic communities

In general, succession in wood occurs over decadal time scales and is initiated

by the penetration of the bark barrier by bark and ambrosia beetles (Scolytidaeand Platypodidae) at, or shortly after, tree death (Ausmus 1977, Dowding 1984,Savely 1939, Swift 1977, Zhong and Schowalter 1989) These beetles inoculategalleries in fresh wood (decay class I, bark still intact) with a variety of symbi-

otic microorganisms (e.g., Schowalter et al 1992, Stephen et al 1993; see Chapter

8) and provide access to interior substrates for a diverse assemblage of trophs and their predators The bark and ambrosia beetles remain only for thefirst year but are instrumental in penetrating bark, separating bark from wood,and facilitating drying of subcortical tissues (initiating decay class II, bark frag-mented and falling off) These insects are followed by wood-boring beetles; woodwasps; and their associated saprophytic microorganisms, which usually dominatewood for 2–10 years (Chapter 8) Powderpost and other beetles, carpenter ants,

sapro-Camponotus spp., or termites dominate the later stages of wood decomposition

(decay classes III–IV, extensive tunneling and decay in sapwood and heartwood,loss of structural integrity), which may persist for 5–100 years, depending on woodconditions (especially moisture content) and proximity to population sources

Wood becomes increasingly soft and porous, and holds more water, as decay gresses These insects and associated bacteria and fungi complete the decompo-sition of wood and incorporation of recalcitrant humic materials into the forestfloor (decay class V)

pro-Insect species composition follows characteristic successional patterns indecaying carrion (Figs 10.3 and 10.4), with distinct assemblages of species defin-

ing fresh, bloated, decay, dry, and remains stages (Payne 1965, Tantawi et al 1996,

Tullis and Goff 1987,Watson and Carlton 2003) For small animals, several carrionbeetle species initiate the successional process by burying the carcass prior

to oviposition Distinct assemblages of insects characterize mammalian versusreptilian carcasses (Watson and Carlton 2003) For all animal carcasses, the fresh,bloated, and decay stages are dominated by various Diptera, especially calliphorids, whereas later stages are dominated by Coleoptera, especially dermestids The duration of each stage depends on environmental conditions

that affect the rate of decay (compare Figs 10.3 and 10.4) (Tantawi et al 1996)

II SUCCESSIONAL CHANGE IN COMMUNITY STRUCTURE 291

FIG 10.3 Succession of arthropods on rabbit carrion during summer in Egypt From Tantawi et al (1996) with permission from the

Entomological Society of America.

FIG 10.4 Succession of arthropods on rabbit carrion during winter in Egypt From Tantawi et al (1996) with permission from the

Entomological Society of America.

and on predators, especially ants (Tullis and Goff 1987, Wells and Greenberg1994) This distinct sequence of insect community types, as modified by local environmental factors, has been applied by forensic entomologists to determinetime since death.

Detritus-based communities develop in bromeliad and heliconia leaf pools(phytotelmata), as well as in low-order stream systems Richardson and Hull

(2000) and Richardson et al (2000b) observed distinct sequences of arrival of

dipteran filter feeders and gatherers during phytotelmata development in Puerto

Rico The earliest colonizer, of barely opened Heliconia bracts, was a small unidentified ceratopogonid, followed by an unidentified psychodid, cf Pericoma Subsequently, phytotelmata were colonized by two syrphids, Quichuana sp and Copestylum sp Older bracts with accumulated detritus and low oxygen concen- tration supported mosquitoes, Culex antillummagnorum, and finally tipulids, Limonia sp., in the oldest bracts.

B Factors Affecting SuccessionSuccession generally progresses toward the community type characteristic of thebiome within which it occurs (e.g., toward deciduous forest within the deciduousforest biome or toward chaparral within the chaparral biome; e.g., Whittaker 1953,1970) However, succession can progress along various alternative pathways and

reach alternative endpoints (such as stands dominated by beech, Fagus, maple, Acer, or hemlock, Tsuga, within the eastern deciduous forest in North America),

depending on a variety of local abiotic and biotic factors Substrate conditions resent an abiotic factor that selects a distinct subset of the regional species pooldetermined by climate Distinct initial communities reflecting disturbance condi-tions, or unique conditions of local or regional populations, can affect the success

rep-of subsequent colonists These initial conditions, and subsequent changes, guidesuccession into alternative pathways leading to distinct self-perpetuating end-points (Egler 1954, Whittaker 1953) Herbivory and granivory can guide succes-

sion along alternative pathways (Blatt et al 2001, Davidson 1993).

Substrate conditions affect the ability of organisms to settle, become lished, and derive necessary resources Some substrates restrict species repre-sentation (e.g., serpentine soils, gypsum dunes, and lava flows) Relatively fewspecies can tolerate such unique substrate conditions or the exposure resultingfrom limited vegetative cover In fact, distinct subspecies often characterize thecommunities on these and the surrounding substrates Contrasting communitiescharacterize cobbled or sandy sections of streams because of different exposure

estab-to water flow and filtration of plant or detrital resources Finally, sites with a highwater table support communities that are distinct from the surrounding commu-nities (e.g., marsh or swamp communities embedded within grassland or forestedlandscapes)

Successional pathways are affected by the composition of initial colonists andsurvivors from the previous community The initial colonists of a site representregional species pools, and their composition can vary depending on proximity

to population sources A site is more likely to be colonized by abundant species

than by rare species Rapidly growing and expanding populations are more likely

to colonize even marginally suitable sites than are declining populations Forexample, trees dying during a period of minimal bark beetle abundance wouldundergo a delay in initiation of heterotrophic succession, dominated by a dif-ferent assemblage of insect species associated with different microorganisms

(e.g., Schowalter et al 1992) Wood initially colonized by decay fungi, such as

inoculated by wood-boring beetles, wasps, and termites, decays more rapidly,thereby affecting subsequent colonization, than does wood initially colonized

by mold fungi, such as inoculated by bark and ambrosia beetles (Käärik 1974,

Schowalter et al 1992).

Many individuals survive disturbance, depending on their tolerance to (or tection from) disturbance, and affect subsequent succession (Egler 1954) Dis-turbance scale also affects the rate of colonization Succession initiated primarily

pro-by ruderal colonists will differ from succession initiated pro-by a combination ofruderal colonists and surviving individuals and propagules (e.g., seed banks)

Such legacies from the previous community contribute to the early appearanceand advanced development of later successional species These may precludeestablishment of some ruderal species that would lead along a different succes-sional pathway Large-scale disturbances promote ruderal species that can colo-nize a large area rapidly, whereas small-scale disturbances may expose too littlearea for shade-intolerant ruderal species and be colonized instead by later suc-cessional species expanding from the edge (Brokaw 1985, Denslow 1985, Shureand Phillips 1991) Fastie (1995) identified distance from each study site to the

nearest seed source of Sitka spruce, Picea sitchensis, at the time of deglaciation

as the major factor explaining among-site variance in spruce recruitment atGlacier Bay, Alaska

The sequence of disturbances during succession determines the composition

of successive species assemblages For example, fire followed by drought wouldfilter the community through a fire-tolerance sieve then a drought-tolerancesieve, whereas flooding followed by fire would produce a different sequence of

communities Harding et al (1998) and Schowalter et al (2003) demonstrated that

arthropod communities in stream and forest litter, respectively, showed responses

to experimental disturbances that reflected distinct community structures amongblocks with different disturbance histories Disturbance also can truncate com-munity development Grasslands and pine forests often dominate sites with cli-matic conditions that could support mesic forest, but succession is arrested bytopographic or seasonal factors that increase the incidence of lightning-ignitedfires and preclude persistence of mesic trees

Longer-term environmental changes (including anthropogenic suppression ofdisturbances) also affect the direction of community development Ironically, firesuppression to “protect” natural communities often results in successionalreplacement of fire-dominated communities, such as pine forests and grasslands

The replacing communities may be more vulnerable to different disturbances

For example, fire suppression in the intermountain region of western NorthAmerica has caused a shift in community structure from relatively open,pine/larch woodland maintained by frequent ground fires to closed-canopy

II SUCCESSIONAL CHANGE IN COMMUNITY STRUCTURE 295

pine/fir forest that has become increasingly vulnerable to drought and standreplacing crown fires (Agee 1993, Schowalter and Lowman 1999, Wickman 1992).The importance of animal activity to successional transitions has not been recognized widely, despite obvious effects of many herbivores on plant species

composition (e.g., Louda et al 1990a, Maloney and Rizzo 2002, Torres 1992;

see Chapter 12) Vegetation changes caused by animal activity often have beenattributed to plant senescence Animals affect succession in a variety of ways(Davidson 1993, MacMahon 1981, Schowalter and Lowman 1999, Willig and

McGinley 1999), and Blatt et al (2001) showed that incorporation of herbivory

into an old-field successional model helped to explain the multiple successionalpathways that could be observed Herbivorous species can delay colonization byhost species (Tyler 1995, D Wood and Andersen 1990) and can suppress or killhost species and facilitate their replacement by nonhosts over areas as large as

106ha during outbreaks (Schowalter and Lowman 1999) Bullock (1991) reportedthat the scale of disturbance can affect animal activity, thereby influencing colo-nization and succession Generally, herbivory and granivory during early sereshalts or advances succession (V K Brown 1984, Schowalter 1981, Torres 1992),whereas herbivory during later seres halts or reverses succession (Davidson 1993,Schowalter and Lowman 1999) Similarly, Tullis and Goff (1987) and Wells andGreenberg (1994) reported that predaceous ants affected colonization and activ-ity of carrion feeders and affected succession of the carrion community

Granivores tend to feed on the largest seeds available, which most often resent later successional plant species, and thereby inhibit succession (Davidson1993) Herbivores and granivores can interact competitively to affect local pat-

rep-terns of plant species survival and succession For example, Ostfeld et al (1997)

reported that voles dominated interior portions of old fields, fed preferentially

on hardwood seedlings over white pine, Pinus strobes, seedlings, and

competi-tively displaced mice, which fed preferentially on white pine seeds over wood seeds near the forest edge This interaction favored growth of hardwoodseedlings in the ecotone and favored growth of white pine seedlings in the oldfield interior

hard-Animals that construct burrows or mounds or that wallow or compact soilscan kill all vegetation in small (several m2) patches or provide suitable germina-tion habitat and other resources for ruderal plant species (D Andersen andMacMahon 1985, MacMahon 1981; see also Chapter 14), thereby reversing suc-cession Several studies have demonstrated that ant and termite nests createunique habitats, usually with elevated nutrient concentrations, that support dis-tinct vegetation when the colony is active and facilitated succession following

colony abandonment (e.g., Brenner and Silva 1995, Garrettson et al 1998, Guo

1998, King 1977a, b, Lesica and Kannowski 1998, Mahaney et al 1999) Jonkman (1978) reported that the collapse of leaf-cutter ant, Atta vollenweideri, nests fol-

lowing colony abandonment provided small pools of water that facilitated plantcolonization and accelerated development of woodlands in South Americangrasslands

Predators also can affect succession Hodkinson et al (2001) observed that

spiders often are the earliest colonizers of glacial moraine or other newly exposedhabitats Spider webs trap living and dead prey and other organic debris In

systems with low organic matter, nutrient availability, and microbial decomposeractivity, spider digestion of prey may accelerate nutrient incorporation into thedeveloping ecosystem Spider webs are composed of structural proteins and mayredistribute nutrients over the surface In addition, webs physically stabilize thesurface and increase surface moisture through condensation from the atmos-phere These effects of spiders may facilitate development of cyanobacterialcrusts and early successional vegetation.

Relatively few studies have evaluated community development tally Patterns of arthropod colonization of new habitats represent a relatively

experimen-short-term succession amenable to analysis D Strong et al (1984) considered the

unwitting movement of plants around the world by humans to represent a naturalexperiment for testing hypotheses about development of phytophage assem-blages on a new resource They noted that relatively few arthropod colonists onexotic plants were associated with the plant in its native habitat Most arthropodsassociated with exotic plants are new recruits derived from the native fauna ofthe new habitat Most of the insects that colonize introduced plants are general-ists that feed on a wide range of hosts, often unrelated to the introduced plantspecies, and most are external folivores and sap-suckers (Kogan 1981, D Strong

et al 1984) Miners and gall-formers represent higher proportions of the

associ-ated fauna in the region of plant origin, likely because of the higher degree ofspecialization required for feeding internally For example, endophages repre-sented 10–30% of the phytophages associated with two species of thistles innative European communities but represented only 1–5% of phytophages asso-ciated with these thistles in southern California where they were introduced (D

Strong et al 1984) These results indicate that generalists are better colonists than

are specialists, but adaptation over ecological time increases exploitation

effi-ciency (Kogan 1981, D Strong et al 1984).

In one of the most ambitious studies of community development, Simberloffand Wilson (Simberloff 1969, Simberloff and Wilson 1969, E Wilson and Simberloff 1969) defaunated (using methyl bromide fumigation) six small man-

grove islands formed by Rhizophora mangle in Florida Bay and monitored the

reestablishment of the arthropod community during the following year berloff and Wilson (1969) reported that by 250 days after defaunation, all but themost distant island had species richness and composition similar to those ofuntreated islands, but densities were lower on treated islands Initial colonistsincluded both strong and weak fliers, but weak fliers, especially psocopterans,showed the most rapid population growth Ants, which dominated the mangrovefauna, were among the later colonists but showed the highest consistency in col-onization among islands Simberloff and Wilson (1969) found that colonizationrates for ant species were related to island size and distance from populationsources The ability of an ant species to colonize increasingly smaller islands wassimilar to its ability to colonize increasingly distant islands Species richness ini-tially increased, declined gradually as densities and interactions increased, thenreached a dynamic equilibrium with species colonization balancing extinction(see also E Wilson 1969) Calculated species turnover rates were >0.67 speciesper day (Simberloff and Wilson 1969), consistent with the model of MacArthurand Wilson (1967)

Sim-II SUCCESSIONAL CHANGE IN COMMUNITY STRUCTURE 297