Environmental Science: Toward A Sustainable Future Chapter 4

Ecosystems Part 1:

Populations and Succession

Lessons Learned in this Chapter

•How biotic potential and environmental resistance control population growth.•Ecological succession: primary, secondary and aquatic.•The third and fourth principles of ecosystem sustainability. (predators preventing overgrazing and ecosystem resilience)•How humans influence the rate and direction of ecosystem change.

Outline of Chapter 4

A. Population dynamics

B. Population equilibrium

C. Inter and Intraspecies Competition

D. Succession

E. Living beyond our means

F. Natural Selection and Evolution

Dynamic Equilibrium

Births

Deaths

A balance between births (B) and deaths (D), along with a balance between immigration (into a pop, I) and

emigration (movements out of a population, E).Population Growth = B – D + I - E

Population Growth Curves

Not sustainable

= K

Biotic Potential Biotic potential: the number of possible offspring produced

under optimal conditions due to Reproductive rate Migration and dispersal abilities Defenses Coping strategies

r = instrinic rate of population growth if had unlimited resources Critical size = minimum size a population needs to support a

breeding population, below this the population is a high risk of becoming extinct

Environmental Resistance combination of biotic and abiotic factors

that may limit population increase Predators, competitors, disease Adverse weather, limited food/nutrients

Carrying capacity (K on pop curves) is the maximum # of individuals than can be sustained indefinitely in a given space

Biotic Potential Vs. Environmental Resistance

Reproductive Strategiesr-strategist K-strategist

Many offspring withlow parental care, successIn instable ecosytems

Few offspring withhigh parental care, prone to extinction

Instrinic rate of population growth is high

Populations tend to remain stable near the carrying capacity (K)

Population Dynamics Factors of environmental resistance are either:

Density-independent controls effects do not vary with population density: e.g., adverse weather, earthquakes, drought, fire, pesticides, habitat destruction

Density-dependent have a greater effect on a pop as the pop density increases: e.g., infectious disease, overgrazing, predation, parasitism, competition for space

Predator-prey Balance:Wolves and Moose on Royal Isle Island

Tipping the Balance: Introduced Species(alien species, invasive species, exotic species)

Rabbits in Australia with no natural predators Domestic cats on islands Zebra mussels in the Great Lakes Chestnut blight fungus from Chinese chestnut

trees

Introduced Species Why have these introductions resulted

in a degradation of the ecosystems? (Think in terms of environmental resistance and biotic potential.)

See text pages 91 to 95 for details on each of these examples

The Third Principle of Ecosystem Sustainability The size of the

consumer population is maintained so that overgrazing or other overuse does not occur.

Rabbit overgrazing on Phillip Island

Mechanisms of Population Equilibrium: Plant-Herbivore

29 reindeer introduced on St. Mathew Island

Mechanisms of Population Equilibrium Absence of natural enemies like

predators allows a herbivore population to exceed carrying capacity which results in overgrazing of the habitat. The herbivore population subsequently crashes.

Balanced Herbivory

Mechanisms of Population Equilibrium of Herbivores Can be both predator-prey (top down)

or plant-herbivore (bottom up) methods of controlling the size of the herbivore population.

How would the herbivore population growth curve look if diseases were used as the control mechanism?

Mechanisms of Population Equilibrium: Plant Diversity Microclimates (shade of trees or in bright

sun, burrows underground, near water edge etc)

Ecological niches: the lifestyles or roles of each species are specialized (specific adaptations)

Balanced herbivory of different types of plant or different parts of same plant

Interspecific Competition and Population Equilibrium Competition between members of different

species can be resolved due to specific adaptations, an example is riparian (water related microecosystems) vs. non-riparian

In Great Plains, grasses in most areas yet riparian woodlands along river banks

In Easter US, sycamore and red maple can thrive in water-saturated soil while oaks and pines require well-drained soil

More Interspecific Competition Adaptations Predator-prey relationships in balance…any eating of another species is a

predator-prey Symbiosis (long lasting relationship in which species live together in

intimate association• Parasitism: parasite benefits and host is harmed (fungus, protozoan,

bacteria, leeches)• Mutualism: both benefit like epiphytes (air growing plants) in rainforest

trees or lichens (photosynthetic algae combined with decomposing fungi)• Commensalism: one benefits other is neutral (ferns growing in shade of

redwood trees) Resource Partitioning for food or shelter or breeding

Intraspecific (within species) Competition and Population Equilibrium

Territoriality: defense of a resource against individuals of the same species Examples of wolves and songbirds Results in priority use of resources for feeding,

breeding and living

Self-thinning to maximize resources In plants physical space is needed In animals, overcrowded conditions can lead to easier

spread of disease, hormone shifts producing less young, cannibalism for survival, etc.

Types of Species in an Ecosystem Native species: normally lives and thrives there Non-native (exotic, alien): immigration of a species naturally,

sometimes an accidental or deliberate introduction by humans Indicator species: serve as early warnings that a community is

damaged, e.g. birds, especially raptors b/c they are quickly effected and trout species present indicate water quality and levels of dissolved oxygen

Keystone species: play pivotal roles in the function and integrity of their ecosystem, e.g. , dung beetles, sea otters with kelp, beavers with beaver pond habitats (46% of endangered animals happen due to lack of beaver ponds), great white shark, elephants in tearing down trees to keep grassland and forest balance

Disturbance and Succession Equilibrium theory: ecosystems are stable

environments and there is an ongoing “balance of nature”

Nonequilibrium theory points out that the “patchiness” of nature within ecosystems indicate ecosystem are always shifting and changing, e.g. due to abiotic distrubances, climate shifts etc

Succession – One groups of biotic populations gradually replaced by others in an ecosystem

primary – new ecosystem where there were no living things before. Cooled lava, receded glacier, mud slide

secondary- ecosystem used to be there. Fire, humans clear an area

Aquatic – (type of secondary) lakes taken over by terrestrial ecosystem

Climax ecosystem- in balance only changes if major interference

Retreat of a glacier to expose bare rock

Primary succession (no soil)•Must create new soil for plants to grow•The first plants to come in are called pioneer species, these include mosses and lichens which collect water, can go dormant in low water situations, and whose acids can break down rock minerals to form soil

Lichen grass shrub pine tree (likes lots of sun and quick grower) hardwood trees (deciduous trees like oak) climax ecosystem

Primary Succession Lichens and Mosses invade an area and provide a

place for soil and water to accumulate. Larger plants germinate in the new soil layer

resulting in additional soil formation. Eventually shrubs and trees will invade the area. First pine (soft wood) then deciduous (hard wood

trees) like oaks, hickories, beeches, maples and fruit trees

Secondary Succession

Aquatic Succession

The Fourth Principle of Ecosystem Sustainability Ecosystems show resilience during a

disturbance

Disturbance and Resilience (recovery) Removes organisms Reduces populations Releases organic nutrients to the soil in dry

climates Creates opportunities for other species to colonize

(lodge pole pine seeds only release in a fire, grasses needs lots of sunlight exposure)

Fires in Ecosystem

Maintain balance of species and energy in ecosystems over the long run.

Beneficial b/c provide nutrients for soil We avoid natural fires, but the problems like Crown

Fires- (not natural) kill the whole tree 1988 Yellowstone fires changed climax ecosystems of

white bark pine trees to huckle berries. Grizzlies ate both

Fire and Succession Fire climax ecosystems: dependent

upon fire for maintenance of existing balance; e.g., grasslands, pine and redwood forests

What significance does this have for humans and where they live?

Resilience Mechanisms After A Forest Fire Nutrient release to soil Regrowth by remnant roots and seeds Invasions from neighboring

ecosystems Rapid restoration of energy flow and

nutrient cycling

Human Impacts: We have… Increased our biotic potential Decreased our environmental

resistance Contributed to the degradation of

ecosystems We are still on an unsustainable J

curve…uh oh!

Human Impacts Introduce species Eliminate natural predators Alter abiotic factors Misunderstand the role of fire Reduce biodiversity

Implications For Humans Protecting and managing the natural environment to

maintain the goods and services vital to human economy and survival.

Establishing a balance between our own species and the rest of the biosphere by living in a sustainable way.

Global CPR is needed: conservation, preservation, and restoration

Find ways to create positive feedback loop tipping points like the marine sanctuaries on Apo Island to protect fisheries pg. 108 for details

Four Principles of Ecosystem Science Ecosystems will change over time Individual species and interactions between

species will have important impacts on ecological processes

Different sites and regions are unique (abiotic and biotic characteristics)

Disturbances are important and frequent events that have a profound impact on the ecosystem

Fifth Principle of Ecosystem Sustainability

Ecosystems depend on biodiversity.

Why is the fifth principle of sustainability important in understanding the following issues? Endangered species Agriculture Biotechnology Medicine