Sunday, December 16, 2007
I didn't make blog entries for a couple of months over the holidays. In January, I enrolled in college and am taking natural resource classes. Since I have to study course materials, I am using this empty blog space for review.
Lecture Notes with internet additions
Evolution and Ecology
- Adaption & natural selection -- 10 - 30 million species or more ??
- Levels of Organization and complexity -- the more complicated the system, the less predictable.
- Ecology defined: The study of the relationship of organisms to their biotic (living) and abiotic (non-living) environment.
Basic Questions
species distributions -- what limits? climate, food, geography, other species (preditors, compeition, disease organisms. Dispersibility -- why is a species here but not here. Easy example; can the species get there? Starlings, killer bees, gypsy moth.
species abundance
abiotic factors: temperature, humidity, moisture, nutrients
What can a species do if factors exceed or do not meet needs: migrate, hibernation, dormancy (artic ground squirrel - can hibernate 9 mo. a year, heart rate from 200-400 bpm to 7-10 bpm, body temp 30 degrees C to 6 degrees C, 80% eduction in metabolism.)
Couch's Spadefoot Toad -- can be dormant for 2 years, responds to sound/vibration of rain (and ATVs)
Redwood logs underseas -- develop ecosystem until they rot, then ecosystem disappears.
European Kestrals. Eat voles which are cyclic from 10 to 1400 per hectare. Can see vole urine which absorbs ultraviolet light. The vole urine is a proximate cue (indicator of an area suitable for the animal).
biotic factors: preditors, food, competitors, diseases, mutualistic species (such as polinators).
Example: mosquitos in Hawaii -- 600 meter limit altitude, higher is too cold. No avian flu virus above 600 meter so native birds can survive.
Monday, December 17, 2007
Communities
- Growth Form and Structure (plants)
- Species richness (varieties) - number of different species
- Relative abundance -- Index of diversity: Number of species times relative abundance.
- Dominance -- influence on rest of community -- example: remove triliums - little effect; remove redwoods -- cascading effect.
- Trophic structure - who eats whom
Clement's and Gleason's views
The term climax community, also described as a climatic climax community, is an ecological term for a biological community of plants and animals which, through the process of ecological succession - the development of vegetation in an area over time - has reached a steady state. This equilibrium occurs because the climax community is composed of species best adapted to average conditions in that area. The term is sometimes also applied in soil development. The idea of a single climatic climax, which is defined in relation to regional climate, originated with Frederic Clements in the early 1900s.
Clements views on communities (1916). Eco communities were "superorganisms". Pplants and animals in a community have a deep and long shared evolution history. They are tightly co-evolved organisms. This is the "balance of nature view."
Gleason (1926). In the 1950s-1970s an alternative individualist concept, derived from the ideas of H. A. Gleason (1939), gained credence which held that communities were largely a coincidence of individualistic species characteristics, continuously varying environments and different probabilities of a species arriving on a given site.
Gleason's views: Eco communities are individualistic. There is a shared tolerance for conditions.
The truth is probably a little of both.
Tuesday, December 18, 2007
Factors influencing abiotic factors
Plots (natural areas) marked from 1 ha to 10,000 ha. Cleared between plots. Change from edge of community to interior. The actual funtional size was much smaller than the plot boundaries. Changes to 100 meters from boundaries.
Wednesday, December 19, 2007
Keystone species
A keystone species is a species that has a disproportionate effect on its environment relative to its abundance, affecting many other organisms in an ecosystem and help in determine the types and numbers of various others species in a community.
Sea Star, a preditor. Pre-removal -- 15 species; post-removal -- 8 species. If the sea star is removed from the ecosystem, the mussel population explodes uncontrollably, driving out most other species, while the urchin population annihilates coral reefs.
In North America, the grizzly bear is a keystone species - not as a predator but as ecosystem engineers. They transfer nutrients from the oceanic ecosystem to the forest ecosystem. The first stage of the transfer is performed by salmon, rich in nitrogen and potassium, who swim up rivers, sometimes for hundreds of miles. The bears then capture the salmon and carry them onto dry land, dispersing nutrient-rich feces and partially-eaten carcasses. It has been estimated that the bears leave up to half of the salmon they harvest on the forest floor. Another ecosystem engineering keystone species is the beaver, which transforms its territory from a stream to a pond or swamp. In the African savanna, the larger herbivores, especially the elephants, shape their environment. The elephants destroy trees, making room for the grass species. Without these animals, much of the savanna would turn into woodland.
Mutualistic species -- at least two organisms aid each other, such as a polinator. Mutualism is any relationship between two species of organisms that benefits both species. This is the relationship most people think of when they use the word "symbiosis." Exampes of Mutualism, Pollination, Seed Dispersal, Corals, Lichens, Mycorrhizal Fungi, Ants and Aphids.
Thursday, December 20, 2007
Competition
Competition among ecologically similar species is the major factor that determines the structure of animal and plant communities. The main question is, can competing species coexist or not, and what are the major factors that affect coexistence. This topic is a bridge between population ecology and community ecology.
Species need to change or die if being out competed.
Intraspecific competition is a particular form of competition in which members of the same species vie for the same resource in an ecosystem (e.g. food, light, nutrients, space). This can be contrasted with Interspecific competition, in which different species compete. For example, two trees of the same species growing close together will compete for light, water and nutrients in the soil. Getting less resources, they will perform poorer than if they grew by themselves (for example lowered growth rates and fewer seed output). Trees have therefore adapted to grow taller or develop larger root systems through natural selection. Grasshoppers provide an animal example. By eating grass, individual grasshoppers deprive their fellow conspecifics of food. This is an example of exploitation competition, which means that the grasshoppers do not interact directly with each other, but have a negative effect on others' growth and reproduction by their effect on a resource (in this case, grass). In other cases, intraspecific competition may be a case of interference competition, in which the animals interact directly. This is the case, most notably, in territorial animals: some individuals actively prevent others from exploiting a given resource, usually food or space. Intraspecific competition is a major factor affecting the carrying capacity of a population (maximum population level supported by the environment). The levelling of population growth at high densities (known as density dependent inhibition) can be seen as an effect of intraspecific competition. Indeed, whereas at low densities organisms do not compete for resources, at higher densities resources become limiting, and the population size can no longer increase. In terms of population growth rate, this produces a sigmoidal curve, which is a familiar sight for ecologists.
Interspecific competition, in ecology, is a form of competition in which individuals of different species vie for the same resource in an ecosystem (e.g. food or living space). The other form of competition is intraspecific competition, which involves organisms of the same species. An example of interspecific competition, if a tree in a dense forest grows taller than surrounding trees, it is able to absorb more of the incoming sunlight. However, less sunlight is then available for nearby trees that are shaded by the taller tree. An example among animals could be the case of cheetahs and lions; since both species feed on the same prey, they are negatively impacted by the presence of the other because they will have less food. Also, lions sometimes steal prey items killed by cheetahs. Competition is only one of many interacting biotic and abiotic factors that affect community structure. Moreover, competition is not always a straightforward, direct interaction. Interspecific competition may occur when individuals of two separate species share a limiting resource in the same area. If the resource cannot support both populations, then lowered fecundity, growth, or survival may result in at least one species. Interspecific competition has the potential to alter populations, communities and the evolution of interacting species. On an individual organism level, competition can occur as interference or exploitative competition.
Interspecific competition which involves no fighting but instead a co-usage of one or more resources is termed exploitative competition. When one species uses available resources better than others -- resource must be limiting. Example: Red-tailed hawk eating voles during day, great horned owl eating voles at night.
Warblers -- to reduce competition they come specialists at different parts of the environment (such as a specific bype of tree.)
Galapagos Island finches -- develope different beak sizes to eat different seed sizes. Over time, species evolve to reduce competition. On the Galapagos Islands, Darwin also saw several different types of finch, a different species on each island. He noticed that each finch species had a different type of beak, depending on the food available on its island. The finches that ate large nuts had strong beaks for breaking the nuts open. Finches that ate small nuts and seeds had beaks for cracking nuts and seeds. Darwin noticed that fruit-eating finches had parrot-like beaks, and that finches that ate insects had narrow, prying beaks. He wrote: "One might really fancy that from an original paucity [scarcity] of birds ... one species had been taken and modified for different ends."
Character displacement refers to the phenomenon where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur but are minimized or lost where the species’ distributions do not overlap. This pattern results from evolutionary change driven by competition among species for a limited resource (e.g. food). The rationale for character displacement stems from the competitive exclusion principle, also called Gause's Law, which contends that to coexist in a stable environment two competing species must differ in their respective ecological niche; without differentiation, one species will eliminate or exclude the other through competition.
Character displacement is an E. O. Wilson term. Where species found together, they were more different than when they were found apart. Such as species A on island 1, species B on island 3, and A and B on island 2. The inference is that the island 2 birds changed to compete less.
Ghost of competition past -- using a past competition cercumstance (unproved) to infer a common pattern. Consider alternatives.
Friday, December 21, 2007
In ecology, a disturbance is a temporary change in average environmental conditions that causes a pronounced change in an ecosystem. Outside disturbance forces often act quickly and with great effect, sometimes resulting in the removal of large amounts of biomass. Ecological disturbances include fires, flooding, windstorm, insect outbreaks, as well as anthropogenic disturbances such as forest clearing and the introduction of exotic species [1]. Disturbances can have profound immediate effects on ecosystems and can, accordingly, greatly alter the natural community. Because of these and the impacts on populations, these effects can continue for an extended period of time.
Primary succession is one of two types of ecological succession and biological succession of plant life, and occurs in an environment in which new substrate, devoid of vegetation and usually lacking soil, is deposited (for example a lava flow). (The other type of succession, secondary succession, occurs on substrate that previously supported vegetation before a disturbance destroyed the plant life.) In primary succession pioneer plants like mosses and lichen plus algae and fungus plus other abiotic factors like wind and water start to "normalize" the habitat, creating conditions nearer the optimum for vascular plant growth; pedogenesis or the formation of soil is the most important process. These pioneer plants are then dominated and often replaced by plants better adapted to less austere conditions, these plants include vascular plants like grasses and some shrubs that are able to live in thin soils that are often mineral based. A good example of primary succession takes place after a volcano has erupted. The barren land is first colonized by pioneer plants which pave the way for later, less hardy plants, such as hardwood trees, by facilitating pedogenesis, especially through biotic acceleration of weathering and the addition of organic debris to the surface regolith.
Example: Bald Hills grazing areas maintained by fire.
Saturday, December 22, 2007
In ecology, energy flow (calorific flow) refers to the flow of energy through a food chain. In following energy flow in an ecosystem, ecologists seek to quantify the relative importance of different component species and feeding relationships.
A general energy flow scenario follows:
- Solar energy is fixed by the photoautotrophs, the so called primary producers, like green plants which fix the energy in forms such as glucose and ATP by photosynthesis.
- The primary consumers consuming these photoautotrophs are herbivores. They absorb most of the stored energy in the plant through digestion, and transform it into the form of energy they need, adenosine triphosphate, through respiration. A part of the energy received by the herbivore is converted to bodily heat (an effect of respiration), which is radiated away and lost from the system. Energy loss also occurs in the expulsion of egesta, which contains undigested energy compounds.
- Secondary Consumers then consume the primary consumers. Energy that had been used by the primary consumers for growth and storage is thus absorbed into the secondary consumers through the process of digestion. As with primary consumers, secondary consumers convert this energy into a more suitable form (ATP) in respiration. Again some energy is lost from the system, since energy which the primary consumers had used for respiration cannot be utilised by the secondary consumers.
- Tertiary consumers then consume the secondary consumers, and most of the energy is passed along, while some is again lost in the ways described above and below.
- A final link in the food chain is decomposers which break down the organic matter of the
of the energy is lost, with some being lost as heat into the environment (an effect of
respiration) and some being lost as egesta. This means the top consumer of a food chain
receives the least energy, as a lot of the food chain's energy has been lost between trophic
levels. This loss of energy at each level limits typical food chains to only 4-6 links.
Lecture Notes
Plants absorb about 1% of energy that falls on them (sunlight). Primary consumers -- herbivoes. Secondary consumers -- carnivores.
Cubic Bulls
3 x 3 x 3 cm -- 54 cm squared : 27 cm cubed -- SA : Vol -- 2 : 1
6 x 6 x 6 cm -- 216 cm squared : 216 cm cubed -- SA : Vol -- 1 : 1
More surface ares results in more heat lost means animal has to eat more.
Within a trophic level we see a larger Standing Crop Biomass of larger organisms than small organisms owing to SA : Vol.
Inefficiencies in energy flow. Energy transfer between trophic levels. 1. Not all plants are sonsumed, not all energy available at trophic level n is consumed by trophic level n + 1. 2. Not all energy consumed is converted to biomass.
In ecology, trophic dynamics is the system of trophic levels (Greek trophe-, food), which describe the position that an organism occupies in a food chain - what it eats, and what eats it.
Ecologists study the energy economies of natural systems. Foundation species (also known as primary producers) harvest an energy source such as sunlight and turn it into biomass. This biomass is consumed by other organisms (primary consumers), which are in turn consumed by others. Each link in this chain of consumption is termed a trophic level. Because only a fraction of the energy used by organisms at each trophic level is converted to biomass, less energy is available at higher levels.
Most ecosystems ultimately rely upon the Sun for energy and upon photosynthetic organisms to harness that energy. There are a few exceptions to this. For example, in deep sea hydrothermal vents and acid mine drainage, chemosynthetic archaea derive energy from the break down of sulfur rich compounds.
In terrestrial ecosystems, plants such as grass are the primary producers and form the first trophic level. Next are herbivores (primary consumers) that eat the grass, such as rabbits. Next are carnivores (secondary consumers) that eat the rabbits, such as a bobcats. Trophic relationships are rarely this simple. Very often they are more of a web than a chain. For example, mountain lions may eat both rabbits and bobcats. The trophic categorization of the mountain lion exists on two levels, possibly more.
Every time there is an exchange of energy between one trophic level and another, there is quite a significant loss due to the fundamental laws of thermodynamics. This means so many units of grass can only support a much smaller number of units of rabbits, who can only support a smaller group of bobcats, who can only support a smaller group of mountain lions. This is why trophic levels are usually portrayed as a pyramid, one that places grass on the bottom and mountain lions on top---the top is always much smaller than the bottom. Each level implies a loss of energy and efficiency and less life that can be supported by the sun.
Trophic levels and biodiversity. Each species in an ecosystem is affected by the other species in that ecosystem. There are very few single prey-single predator relationships. Most prey are consumed by more than one predator, and most predators have more than one prey. Their relationships are also influenced by other environmental factors. In most cases, if one species is removed from an ecosystem, other species will most likely be affected, in ways such as extinction.
Biodiversity (seen from the viewpoint of species diversity) is a major contributor to the stability of ecosystems. When an organism can exploit a wide range of resources, a decrease in biodiversity is less likely to have an impact. However, for an organism which can only exploit a limited range of resources, a decrease in biodiversity is more likely to have a strong effect. David Tilman is an ecologist who has done a lot of work establishing the theoretical basis of this phenomenon.
Reduction of habitat, hunting and fishing of some species to extinction or near extinction, and eradication of insects and pollution tend to tip the balance of biodiversity. Similarly, in-situ conservation areas need to be carefully designed to maintain a diverse and stable environment for the threatened species to thrive.
