Chapter 20- Principles of Ecology
Biosphere
The concentration of atmospheric plays a role in the regulation of global temperature.
Region
Geologic history influences regional diversity within certain groups of organisms.
Landscape
Vegetated corridors affect the rate of movement by mammals among isolated forest fragments.
Ecosystem
Fire affects nutrient availability in grassland ecosystems.
Community
Factors influence the number of large mammal species living together in African grasslands.
Interactions
Predators influence where zebras feed in the landscape.
Population
Factors control zebra populations.
Individuals
Zebras regulate their internal water balance.
Glacier Bay, Alaska
Calvin Coolidge designated it a national monument in 1925.
Expanded by Jimmy Carter in 1978.
UNESCO World Heritage Site in 1979, Biosphere Reserve in 1986.
Managed by the National Park Service.
Receives > 400,000 visitors annually.
Vancouver's Observations
In the late 18th century, Vancouver described the area as having two large open bays terminated by compact solid mountains of ice.
He estimated the glacier was 4000’ thick and up to 20 miles wide.
John Muir's Exploration
In 1879, about 85 years later, John Muir explored the Alaska coast.
Muir found that the glacier had retreated 30 – 40 km from Vancouver's original observations.
Glaciers and Mountain Ranges
Mountain ranges in Europe and Asia generally run east to west.
Isolated mountain ranges are often islands of distinctive climate.
Muir Glacier, Alaska
The retreat of the Muir Glacier is visually depicted through a series of images from 1941, 1950, and 2004.
William S. Cooper and Succession
William S. Cooper, an ecologist, read Muir’s work (published in 1915) and became interested in how ecosystems change over time.
Cooper first visited Glacier Bay in 1916.
He recognized Glacier Bay as a natural laboratory with a known glacial history dating back to 1794 (Vancouver).
Succession is defined as the gradual change in plant and animal communities in an area following disturbance or the creation of new substrate.
Disturbance is an event that disrupts an ecosystem, such as a wildfire or human activity, allowing new species to establish themselves. Creation of new substrate occurs when new surfaces are formed, like after a volcanic eruption or glacial retreat, starting the ecological succession process from scratch.
This process of succession can be categorized into primary succession, where life begins in lifeless areas, and secondary succession, which occurs in previously occupied areas that have undergone disturbance.
Succession
Glacier recedes, exposing bare ground.
First 20 years: horsetail, willows, cottonwood seedlings, mountain avens, Sitka spruce.
Pioneer Community: the first community, in a successional sequence, to be established following a disturbance.
After 30 years: dwarf shrubs dominant, some alder, willow, cottonwood, Sitka spruce.
After 40 years: alder thickets dominant.
After 50-70 years: Cottonwood and Sitka Spruce cover 50% of areas.
After 75-100 years: Spruce forest dominant, mosses in understory, some hemlock.
Longer: Hemlock replaces spruce, depending on topography may become muskeg.
Climax Community: A community that occurs late in succession.
Climax Community
Biomes (large scales).
Local topography effects.
Well-drained = Hemlock forest.
Poorly drained = Muskeg.
Clements & Gleason - Two Contrasting Views of Vegetation Associations
Clements (1936) viewed the climax as the major unit of vegetation, forming the basis for the natural classification of plant communities.
He emphasized the intimate relation of climax and climate.
Succession and Disturbance
Primary Succession: Succession on newly exposed geological substrates, not significantly modified by organisms (e.g., volcanic lava, glacial retreat).
Secondary Succession: Succession where disturbance has destroyed a community, without destroying the soil (e.g., forest fire, logging).
Similar processes, different time scales.
Community Changes During Succession
Increases in species diversity.
Changes in species composition.
Primary Succession at Glacier Bay - Reiners et al. (1971)
Succession depends on topography and age.
Control for topography to study the effect of age.
Succession, the process of ecosystem development over time, is influenced by the shape and features of the land (topography) as well as how long a particular area has been undergoing changes (age). To understand how the age of an ecosystem affects its development, researchers control for topography, meaning they investigate areas with similar landforms to ensure that any observed effects on succession are due to age alone rather than variations in the landscape.
8 sites.
10 – 1,500 years old.
Below 100m, moderate slopes, glacial till.
Primary Succession Stages
10 years: Willowherbs, horsetails, willow.
23 years: Pioneer species, Cottonwood, Dryas shrubs.
33 years: Dryas shrubs, clumps of willow, cottonwood, alder.
44 years: Dryas shrubs and open patches.
108 years: Thicket of alder and willow, cottonwood and spruce canopy.
200 years: Spruce forest.
500 years: Hemlock forest, few spruce.
Species Richness Changes
Mosses: Increase to mid-succession then stable.
Trees & Tall Shrubs: Increase to mid-succession then decrease.
Low shrubs & herbs: Increase throughout.
Community Changes During Succession
Reiners et al. (1971) studied changes in plant diversity during succession using a chronosequence of sites, which initially appeared to increase in diversity over time.
Buma et al. (2019) found that there wasn’t actually a consistent progression of species; diversity either stayed the same or decreased, and initial species mattered.
Secondary Succession in Temperate Forests
Jamestown, Virginia: Settled in 1607.
As colonization expanded, there was a history of forest clearing and abandoned agriculture, with few remaining areas of undisturbed forest.
Piedmont Plateau.
Oosting (1942) studied secondary succession in the Piedmont Plateau of North Carolina.
Abandoned Field Successional Sequence
Crabgrass, horseweed.
Year 2: aster, ragweed.
Few years: broomsedge, some shrubs, small trees, pine seedlings.
10-15 years: closed pine canopy.
40-50 years: pine forest with deciduous understory.
150 years: oak, hickory forest, few pines.
Number of Species
The number of woody plant species begins to level off after about 100 to 150 years.
The number of bird species leveled off after 50 to 100 years of forest succession.
Succession in the Rocky Intertidal Zone
Sousa (1979) cleared and stabilized boulders.
Green algae (Ulva sp.), Cthamalus barnacles.
Red algae (e.g., Gelidium coulteri, Gigartina leptorhynchos).
One red algae overgrows everything to dominate 60 – 90% of the space (Gigartina canaliculata).
Number of Species Over Time
The number of species of macroinvertebrates and macroalgae leveled off between 1 and 1.5 years.
Succession in Streams After Flash Flooding
Flash flood eliminates 98% of algal and invertebrate biomass.
Day 2: bare sand, diatoms.
Day 5: half covered by diatoms.
Day 13-22: all diatoms.
Day 35: blue-green algae, green algae.
Day 63: diatoms, blue-green algae, green algae.
Temporal Pattern of Species Richness
Algal species diversity (H') over days after flooding shows how diatoms are replaced by other algae.
Ecosystem Changes During Succession
Ecology: biotic and abiotic.
“Organisms acting upon mineral substrates contribute to the building of soils”.
“Soils, in turn, strongly influence the kinds of organisms that grow in a place.”
Ecosystem Change Over Millions of Years
Hawaiian Islands formed as tectonic plate moves across hotspot.
Oldest islands 4.1 million years.
Hawaii youngest.
Fresh lava – 150,000 years.
Hedin et al. (2003)
Similar climate (temperature, precipitation).
All islands with forest dominated by native tree Metrosideros polymorpha.
Kauai: 4,100,000 years.
Molokai: 1,400,000 years.
Hawaii: 150,000 years.
Hedin et al. (2003) - Soil Age and Nutrients
Both organic carbon and total nitrogen peaked after approximately 150 thousand years of soil development.
Refractory = not available to plants. Shifts in available nutrients.
Hedin et al. (2003) - Ecosystem Limitation
Ecosystem is initially limited by nitrogen.
Later, ecosystem is limited by phosphorous.
Succession and Stream Ecosystem Properties
Sycamore Creek, Arizona had rapid biomass increase following flooding, then slower rates.
Algal and invertebrate biomass.
Gross primary production, total ecosystem respiration, and nitrogen retention showed similar pattern.
Succession causes changes in species composition and diversity, and changes structure and function of ecosystems.
Ecosystem Processes During Succession
Photosynthetic rate measured by oxygen production, respiration by oxygen consumption.
Both primary production and respiration began to level off in less than a month after flooding.
Mechanisms of Succession
Facilitation: Only early successional species can establish. First species to establish modify environment. Environment less suitable for early species but more suitable for late successional species: early successional species die out. Eventually resident species are ones that do not change environment in a way to favor other species.
Tolerance: Any species able to survive as adults establishes. Environment less suitable for early species but neither less nor more favorable for later successional species. Eventually resident species are ones able to tolerate environmental change by earlier species and no other species can tolerate conditions.
Inhibition: Environment less suitable for establishment by all species. Resident species inhibit establishment of all other species; persist until disturbed. Disturbance destroys climax stage.
Mechanisms of Succession
Facilitation model: Pioneer species modify the environment, making it less suitable for themselves and more suitable for later successional stages.
Tolerance model: Climax species can be present early in succession; later successional species are simply those tolerant of environmental conditions early in succession.
Inhibition model: Early occupants modify the environment, making the area less suitable for both early and late successional species.
Facilitation Model
Many species may attempt to colonize newly available space.
Only certain species will initially establish.
Colonizing pioneer species modify the environment so it becomes less suitable for themselves and more suitable for species of later successional stages.
Climax community occurs when resident species no longer facilitate colonization by additional species.
Tolerance Model
Initial stages of colonization are not limited to pioneer species.
Juveniles of species that dominate at climax may be present throughout succession.
Early successional species do not facilitate later successional species.
Later species enter the system if they tolerate the environmental conditions.
Climax community occurs when the list of tolerant species has been exhausted.
Inhibition Model
Any species can colonize during early succession.
Early occupants modify the environment, making it less suitable for both early and late successional species.
Early arrivals inhibit later colonization.
Later successional species invade only if space is opened up by disturbance.
Succession ends with long-lived, resistant species that come to dominate.
Succession in the Rocky Intertidal Zone
Early succession species => Less suitable for later succession.
Sousa (1979) study:
Early: Ulva.
Mid: Gelidium coulteri, Gigartina leptorhynchos.
Late: Gigartina canaliculata.
Succession in the Rocky Intertidal Zone
Early: Ulva.
Mid: Gelidium coulteri, Gigartina leptorhynchos.
Late: Gigartina canaliculata.
Remove G. coulteri, G. leptoryhnchos.
Ulva recolonizes.
Mid succession species => Less suitable for early succession.
Both findings consistent with the inhibition model.
Facilitation in the Rocky Intertidal - Turner (1983)
Winter waves clear space in lower intertidal.
Ulva green algae first colonist.
Red algae.
Surfgrass Phyllospadix scouleri (barbed projections on seeds).
Clear 0.25 plots in Sept. prior to seed dispersal.
Control plots left alone.
Facilitation in the Rocky Intertidal - Turner (1983)
Check in March, found 48 seeds.
46 on control plots, 2 on removal plots.
2 seeds on removal plots anchored to red algae that was missed during removal.
Over 3 years, found 298 Phllospadix seeds.
Every one attached to middle successional algae.
Middle successional species facilitate recruitment of late successional species.
Facilitation model.
Secondary Succession in Temperate Forests - Keever (1950)
Early abandoned field successional sequence (first few years):
Crabgrass.
Horseweed.
Aster.
Broomsedge.
Secondary Succession in Temperate Forests - Keever (1950)
Early abandoned field successional sequence (first few years):
Crabgrass.
Horseweed (inhibition).
Aster (facilitation).
Broomsedge.
Mechanisms of Primary Succession Following Deglaciation
Pioneer (Nitrogen fixing).
Dryas.
Alder.
Spruce.
Succession and Ecosystem Recovery Model
Proposed by Bormann and Likens.
Reorganization (10 – 20y): Continued biomass and nutrient loss despite plant regrowth.
Aggradation (>100y): Ecosystem accumulates biomass, reaches peak biomass.
Transition phase: Biomass declines from peak.
Steady state phase: Succession and Stability.
Community and Ecosystem Stability
Community stability may be due to lack of disturbance or community resistance or resilience in the face of disturbance.
Definitions
Stability: The persistence of a community or ecosystem in the face of disturbance, usually as a consequence of a combination of resistance and resilience; the absence of change.
Resistance: The capacity of a community or ecosystem to maintain structure and/or function in the face of potential disturbance.
Resilience: The capacity to recover structure and function after disturbance; a highly resilient community or ecosystem may be completely disrupted by disturbance but quickly returns to its former state.
Park Grass Experiment (UK)
Continuous ecological monitoring and experimental protocol from 1856.
Different fertilizer treatments.
Park Grass Experiment (UK)
Community composition: 1910 – 1948.
Recorded from 1862 but allow period of adjustment to fertilizer treatments.
Plot 3: no fertilizer.
Plot 7: P, K, Na, Mg.
Plot 14: N, P, K, Na, Mg.
Legumes, grasses, other species.
Park Grass Experiment (UK)
Variation due to precipitation, but otherwise stable community.
Started as meadow, stayed a meadow.
Starting group proportions remained similar.
Individual plant species varied dramatically.
Question of stability depends on scale.
Replicate Disturbances and Desert Stream Stability
Valett et al. (1994) studied interaction between surface and subsurface waters of Sycamore Creek.
Looked at hydrological linkages between waters that could increase nitrogen supply.
Upwelling zones have highest nitrate concentrations and highest algal production.
Rate of ecosystem recovery higher in upwelling zones.
Spatial relationships of zones in creek is stable.
Resistant to disturbance.
Stability due to geomorphology.