Disturbance Ecology: Complex Interactions Kyle Apigian Christa DagleyIgor Lacan 18 November 2003

Disturbance Ecology: Complex Interactions

Kyle Apigian Christa Dagley Igor Lacan

18 November 2003

Disturbance Ecology: Complex Interactions

Interacting Factor

Disturbance

Effects and Example Study

Other forms of disturbance

A dominant species decline over time;

Changes in long-leaf pine forests

Organism behaviorShift in resource exploitation;

Storm disturbance in kelp forest

Trophic constraints & phenotypic variation

Change in selection pattern;

Darwin’s finches during droughts/El Niño

Predation & body plan variation

Altered succession and composition;

Fish and storms in tropical creek

CompetitionAltered community composition;

Indirect and toxic effect of a pollutant

• Longleaf Pine

• (Pinus palustris)

Complex Interactions

• Fire-dependent ecosystem– summer lightning fires – 2-8yr FRI

• Most species rich vascular plant communities found in the temperate zone

• Pine savannas - highest level of endemism in N. America

• Today only 3% of its original acreage remains


• Contributing factors include:

• naval stores • logging • competition • feral hogs• intensive forestry• fire exclusion



• First product

• Uses: seal cracks on wooden ships, preserve ropes and sails.




• Competition

– loblolly and other pines– large seeds eaten by birds, rodents and

insects – irregular seed production



• naval stores • logging • competition • feral hogs

– 20 seedlings/ha vs. 14,826 s/ha

• intensive forestry• fire exclusion



• naval stores • logging • competition • feral hogs• intensive forestry

– very poor survival– perceived slow early growth

• fire exclusion




– grass stage– thick bark– good self pruner


• Effects of chronic human activities on invasion of longleaf pine by sand pine

• Florida Panhandle

• Landscape Level: aerial photography to quantify the extent and expansion of sand pine.

• Population Level: 12 stands sampled to verify photo interpretation and assess successional trends

• To assess past vegetation patterns and land-use activities, qualitative data for the area was collected

Complex Interactions McCay (2000)


Total = 41,900 ha

• Noninvasive - Stands with no longleaf pine in the canopy.

Complex Interactions Distribution of SP establishment in 5-yr intervals

Grazing discont.

Turpentining ceased Fire suppression

• Conclusions:

• “sand pine invasion occurred b/c of the complex interaction of several factors that increased the susceptibility of LL to enchroachment”

• Turpentining

• competition

• LL crop failures

• fire suppression

• logging


• Effects of fire regime and habitat on tree dynamics

• 8 year study• sandhills and flatwoods sites• Fire frequency (annual or biennial) • Fire season (8 different times throughout

the year) • Limited fire temperature and intensity

data taken

• Looked at recruitment, growth, mortality, change in density and BA, and species composition.

Complex Interactions Glitzenstein et. al (1995)

• Results:

• No systematic or predictable effects of season or frequency of burning on LL dynamics.

• Deciduous oaks were most vulnerable to burning in the early growing season (higher mortality, decline in BA and density).

• Spring/summer burns = LL dominated forests

• Dormant season burns = gradual decrease in LL and shift to oak dominated


• Take Home Message:

• “Long-term persistence of LL, and perhaps other fire-

adapted species in frequently burned LL-dominated

communities, may be determined by complex

interactions between habitat factors and fire

regimes”.


• References

• Glitzenstein, J.S., W.J. Platt, and D.R. Streng. 1995. Effects on fire regime and habitat on tree dynamics in N. Florida longleaf

pine savannas. Ecological Monographs. 65(4):441-476.

• McCay, Deanna. 2000. Effects of chronic human actvities on invasion of longleaf pine forests by sand pine. Ecosystems. 3: 283-

292.

• Outcalt, Kenneth. 2002. The Longleaf pine ecosystem of the south. Native Plants Journal. 1(1) 42-51.


Southern California reef – Kelp, sea urchins, and surfperchbehavioral responses of urchins and fish after storms

Galapagos Islands – Darwin’s finchesbehavioral and phenotypic responses to drought and El Nino

Severe storm disturbances and reversal of community structure in a southern California kelp forestA.W. Ebeling, D.R. Laur and R.J. Rowley. 1985. Marine Biology 84, 287-294

From Ebling et al 1985

Post storm 1: Kelp canopy removed – drift kelp lost Urchins left crevices to find food – ate standing kelp and algal turf Urchin population poorly regulated – reef became a barrens

Post storm 2: Storm killed off exposed urchins Kelp resettled in great abundance

Same disturbance resulted different (reverse) effects depending on prior community structure


Surfperch feed on benthic arthropods that live in the algal turf

Loss of algal turf caused a decline in surfperch populations


Storm effects were not equal across reef, some microhabitats (reef slope, reef crest) retained algal turf

5 surfperch species converged in terms of microhabitat usage

Diet was not significantly affected

Less aggressive, generalist fish left early in season competitive exclusion?

From Stouder 1987

Storm effects were not equal across reef, some microhabitats (reef slope, reef crest) retained algal turf

5 surfperch species converged in terms of microhabitat usage

Diet was not significantly affected

Less aggressive, generalist fish left early in season competitive exclusion?

From Stouder 1987

Darwin’s finches: effects of climactic disturbances on population structure and natural selection

From Grant 1986

Rainfall on the Galapagos

Galapagos islands: high inter-annual variability in rainfalldrought years – little or no rainEl Niño years – excessive rain

From Grant et al 2000

Ex. 1. Geospiza conirostris: large cactus finch

High intraspecific variation in beak size and shape in this species: From long and pointed to shorter and deep.

Beak shape is related to foraging success in one of 3 foraging modes during the dry season:

1. Hammering Opuntia (cactus) fruits long, pointed bills2. Seed cracking long, deep bills3. Stripping bark (to obtain arthropods) deep bills

From Grant and Grant 1989


Extreme rain followed by drought affectedfood supply (cactus fruit and flowers)

Birds with long, pointed bills were at aselective disadvantage.

Birds with deep bills could exploit otherfoods



Primary foraging mode:

Small seeds

Large hard seeds

Ripping Opuntia cactus pads to obtain arthropods

From disruptive to directional selection: Variety of beaks favored in normal years large deep bills favored after disturbance


Ex. 2. Geospiza fortis: medium ground finch - DROUGHT

Drought of 1977: resulted in 85% decline in finch population on Daphne Major

Decline was highly correlated with a decline in seed abundance

From Boag and Grant 1981


Effects of this disturbance on population structure were non-random: large birds more likely to survive than small birds

Large, hard seeds became proportionally more abundant during the drought, as competition for small seeds became intense

Large birds (with large bills) could crack the remaining hard seeds



The drought of 1977 resulted in phenotypic changes to the G. fortis population


Proportional increase in fitness

Body size

Bill “pointedness”


Ex. 3. Geospiza fortis and G. scandens – EL NINO

Caterpillar abundance is significantly greater during El Niño events


Ex. 3. Geospiza fortis and G. scandens – EL NINO

Exceptional rains resulted in increases in total seed biomass

The proportion of small seeds in the environment increased significantly

From Gibbs and Grant 1987a

Summary. Geospiza fortis and G. scandens

Selection during drought years is for large birds

Selection during El Niño is for smaller birds with smaller beaks.

Why? More efficient handling of small seeds? Better competitors with smaller finches?

From Gibbs and Grant 1987b

Conclusions:

Behavioral shifts following a disturbance event can have effects on multiple trophic levels

Individuals with phenotypic traits far to one end of the population distribution may be favored following a disturbance

Climactic disturbances, such as droughts and El Nino, can exert strong selection pressure on populations.

References• Boag, P. T. and P. R. Grant. 1981. Intense natural selection in a population of Darwin’s finches. Science 214: 82-85.• Ebeling, A. W., D. R. Laur, and R. J. Rowley. 1985. Severe storm disturbances and

reversal of community structure in a southern California kelp forest. Marine Biology 84: 287-294.• Grant, B. R. 1985. Selection in bill characters in a population of Darwin’s finches: Geospiza conirostris on Isla Genovesa, Galapagos. Evolution 39(3): 523- 532.• Grant, B. R. and P. T. Grant. 1989. Natural selection in a population of Darwin’s finches. American Naturalist 133(3): 377-393.• Grant, P. R. 1986. Ecology and Evolution of Darwin’s Finches. Princeton University Press, Princeton, NJ.• Grant, P.R., B. R. Grant, L. F. Keller, and K. Petren. 2000. Effects of El Nino events on Darwin’s finch productivity. Ecology 81(9): 2442-2457.• Gibbs H. L. and P. R. Grant. 1987. Ecological consequences of an exceptionally strong El Nino event on Darwin’s finches. Ecology 68(6): 1735-1746.• Gibbs H. L. and P. R. Grant. 1987b. Oscillating selection on Darwin’s finches. Nature 327: 511-513.• Price, T. D., P. R. Grant, H. L. Gibbs, and P. T. Boag. 1984. Recurrent patterns of natural selection in a population of Darwin’s finches. Nature 309: 787- 789.• Stouder, D. J. 1987. Effects of a severe- weather disturbance on foraging patterns within a California surfperch guild. Journal of Experimental Biology and Ecology 114: 73-84.17

Complex Interactions: Aquatic Ecosystems - General

Pringle and Hamazaki, 1997

Effects of Fishes on Algal Response to Storms in a Tropical Stream

or“…how trophic factors interact with disturbance to affect

community response.”



Methods

• Colonization tiles – For algae, macroinvertebrates– Fish exclosures (electric!) vs. controls

• Sampled tiles for algae, macroinvertebrates• Three large storms during the experimental

period– On days 10, 26, and 39-40

• ANOVA



Results 1: Algal Biovolume

“Fig. 2”



Results 2: Algal Community Composition

“Fig. 4”



Results 3: Percent Change in Ecosystem Parameters

“Table 4”



Discussion• Fish present: diatoms cyanobacteria

• Storms: regularly remove diatoms

• No trophic cascade– Omnivory in fishes…. Or regular storms…

• “Omnivorous fishes play a key role in maintaining stability of benthic algal communities and their resistance to

hydrologic disturbance”

Complex Interactions: Aquatic Ecosystems - Pollutants

Johnston and Keough, 2003

Competition Modifies the Response of Organisms to Toxic Disturbance

orAscidians vs. Serpulids:

Toxic and Indirect

Effects of Copper



Methods

• 2 Experiments– Frequency and Intensity: dose toxicant

• 2 doses, 2 frequencies

– Space: dose toxicant + remove competitors

• Sampled for density of Ascidians and Serpulids

• ANOVA



Results 1: Ascidians reduced

from

“Fig. 2”



Results 2:

Most Serpulids increased

from

“Fig. 3”



Results 3: Space

from

“Fig. 4”



Results Summary



Discussion

• Frequency substitutes for intensity

• Copper effects on serpulids: an integration of– Indirect effects: releases space

– Direct effects: toxicity (species-specific)

• “Good Competitor vs. Good Disperser” tradeoff– Episodic pollution favors …

Complex Interactions: Aquatic Ecosystems – More Pollutants

Courtney and Clements, 2000

Sensitivity to acidic pH in benthic invertebrate assemblages with different histories of exposure

to metals

• A microcosm experiment• Interaction between 2 disturbance forces (pollutants) that

are sequential in time• Previous exposure to metals increases sensitivity to low pH• A species-level response scales up to assemblage level

Complex Interactions – Aquatic EcosystemsReferences

• Courtney, L. A., and W. H. Clements. 2000. Sensitivity to acidic pH in benthic invertebrate assemblages with different histories of exposure to metals. J. N. Am. Benthol. Soc. 19(1): 112-127

• Johnston, E. L., and M. J. Keough. 2003. Competition modifies the response of organisms to toxic disturbance. Mar. Ecol. Prog. Ser. 251: 15-26

• Pringle, C. M., and T. Hamazaki. 1997. Effects of fishes on algal response to storms in a tropical stream. Ecology 78(8): 2432-2442

• Salminen, J., B. T. Anh, and C. A. M. Van Gestel. 2001. Indirect effects of zinc on soil microbes via a keystone Enchytraeid species. Env. Toxicology and Chemistry 20(6): 1167-1174

• Morrison, H. A., D. M. Whittle, and G. D. Haffner. 2000. The relative importance of species invasions and sediment disturbance in regulating chemical dynamics in western Lake Erie. Ecological Modelling 125: 279-294

Documents

Disturbance Ecology: Complex Interactions Kyle Apigian Christa DagleyIgor Lacan 18 November 2003