Energy Flow through Trophic Levels and Community Ecology

A ____________ occurs when a depressed area in the earth fills with rainwater or when an animal deposits dung. When an elephant deposits dung on the ground, it creates a new habitat for a species that feed on the dung, such as dung beetles.

disturbance

In a simple trophic cascade in which wolves eat elk, the input is energy from the _________ and the output is energy in the _________. Ecological efficiency measures would tell you the:

elk, wolves -share of energy in the elk that gets passed along to the wolves

How does the extinction rate differ between a large and small island?

-extinction occurs more quickly on smaller island because population sizes are lower and resources are scarcer -this difference creates different equilibrium levels of species on a small island and a large island: a large island will have higher species richness than a small island

What occurs in an extinction and colonization?

-extinction removes species from a community -colonization adds species to a community -both can impact community structure, diversity, and change in communities

What is the ecological efficiency of the forest ecosystem?

-gross primary productivity is 100 units of energy, of this 50 are used by autotrophs for respiration, leaving 50 as net primary productivity -of the 50 units of NPP, 5 are consumed and 45 are not consumed -of the 5 consumed, 1 is assimilated and 4 are egested -of that 1 unit, 0.5 is used for heterotrophic respiration and 0.5 end up in secondary production -consumption efficiency= 5/50= 10%, assimilation efficiency= 1/5= 20%, production efficiency= 0.5/1= 50% -ecological efficiency= 10% x 20% x 50%= 1%

What is the ecological efficiency of grasslands?

-gross primary productivity is 100 units of energy, of this, 50 units are used by autotrophs for respiration, leaving 50 as net primary productivity -of the 50 units of NPP, 30 are consumed and 20 are not consumed -of the 30 consumed, 6 are assimilated and 24 are egested -of the 6 assimilated, 3 are used for heterotrophic respiration and 3 end up in secondary production -consumption efficiency= 30/50= 60%, assimilation efficiency= 6/30= 20%, production efficiency= 3/6= 50% -ecological efficiency= consumption efficiency x assimilation efficiency x production efficiency= 60% x 20% x 50% = 6% of the NPP gets passed on to the next trophic level

What is the evolutionary rate hypothesis?

-higher temperatures in the tropics increase the rate of physiological processes, generation times, and mutation, which leads to increased rates of speciation -the problem with this hypothesis is that a 2018 study on marine fishes (like ray-finned fishes) have suggested that while species richness is greatest in the tropics, the rate of speciation is actually greatest at the poles, which suggests the extinction rate must also be high in the poles

Do islands in the ocean or areas on the mainland have more species diversity?

-islands have fewer species and islands farther away from the mainland have fewer species than islands closer to the mainland -islands that are smaller have less species than larger islands

Does net production efficiency increase or decrease as you move up trophic levels?

-it decreases because predators at the top of the food chain must expend a lot of energy -they must remain constantly alert and be able to run or fly quickly to capture their prey -as a result, they use more of the energy for maintenance and survival, leaving less for growth and the creation of offspring -because gross production efficiency depends on net production efficiency, it decreases as you move up trophic levels as well

Does assimilation efficiency increase or decrease as you move up trophic levels?

-it increases, which suggests that primary consumers have to eat a lot of low-quality food, while carnivores higher up the food chain eat a smaller amount of higher quality food -there is less biomass available to secondary consumers than to primary consumers, but secondary consumers can compensate with high assimilation efficiencies

What are other organisms in a community besides plants and animals?

-microbes are important -decomposers are essential for recycling materials in communities and ecosystems -organisms (plants, animals, and microbes) are all linked by feeding relationships and their interactions

How does succession differ on a community level compared to a level of the ecosystem?

-on a community level, succession means a change in the number and abundance of species over time and in general, the number of species increases rapidly during succession but then levels off at some point -for example, as succession progresses, early colonizers will begin to disappear -at the level of the ecosystem, succession means changes in plant nutrient content, biomass, ecosystem respiration, and photosynthesis -nutrient content, moisture, and organic matter in the soil will change as succession progresses

How does colonization and extinction affect species richness, according to the island equilibrium model?

-on every ecological island of a given size and distance from the mainland, species richness will eventually reach an equilibrium point, where colonization equals extinction -the equilibrium point tells us the number of species (not the type) on the island and the equilibrium turnover rate (there can be constant species turnover in which new species are introduced through colonization and existing species are removed by extinction) -as the number of species on the island increases, the rate of colonization falls because the probability of a new species arriving declines -the rate of extinction rises because competition becomes more intense, and as the average population sizes decrease, the probability of a chance extinction increases

Why is the ecological efficiency of a forest lower than the ecological efficiency for grasslands?

-overall efficiency is lower for the forest than the grassland because while assimilation and production efficiency were the same, consumption efficiency was lower for the forest -in a grassland, most of the energy is stored in the form of grass, which is easily accessible -in a forest, most of the energy is stored in the form of trees, which are harder to consume because trees are protected with bark

At what trophic level is net primary productivity consumed?

-primary consumers consume NPP and assimilate a portion of that energy into their bodies -secondary consumers consume the primary consumers and assimilate a portion of that energy into their bodies -tertiary consumers consume the secondary consumers and assimilate a portion of that energy into their bodies -quaternary consumers consume the tertiary consumers and assimilate a portion of that energy into their bodies

When are r-strategists and k-strategists most abundant during the stages of succession?

-r-strategists are most abundant during the early stages of succession, when resources are abundant -as the population approaches carrying capacity and resources become more scarce, K-strategists begin to dominate

What is species evenness, a function of community structure?

-refers to relative abundance and describes the proportion of each species in the community -for example, if we have 4 species of trees in a community, one might dominate and be 80% abundant, whereas the other species might account for much smaller percentages of the organisms in the community

What is evapotranspiration?

-refers to the evaporation of water from soil plus the transpiration of water from plants -is a good measure of both solar energy input and water availability -species richness increases as evapotranspiration increases, emphasizing climate is a factor that affects species richness

What is production efficiency?

-refers to the percentage of assimilated energy that contributes to new biomass in the form of growth and reproduction -= (production at your level (energy for growth and offspring))/assimilated energy) x 100

What is Lindeman's trophic efficiency?

-refers to the proportion of total population transferred from one trophic level to the next -only about 10% of the energy from one trophic level is converted to biomass at the next highest trophic level, on average -lowest trophic level: 100% (1000 J), second-highest: 10% (100 J), third highest: 1% (10 J), apex predator: 0.1% (1 J) (of energy from lowest trophic level is converted into biomass by the apex predator)

What is species richness, a function of community structure?

-refers to the total number of species in a community and alone does not tell us much about a community -even if we had a community with 100 different species, if one of those species accounted for 99% of all the organisms in that community, the community would not be very diverse -in a given community, there may be four different species of trees, this is a measure of species richness

What is ecological/trophic efficiency?

-represents the share of energy at one trophic level that gets passed on to the next trophic level, in the form of energy for growth and energy in offspring -describes how good an entire trophic level is at finding food and using it to grow and produce offspring - = (production at your level (energy for growth and offspring))/net production from previous level) x 100 -on average, only about 10% of the energy at one trophic level is passed on to the next trophic level

What is the species-energy hypothesis?

-species diversity is higher near the equator because the environment can accommodate more individuals: tropical climates tend to be hot and wet, promoting species richness -the climatic influences on species include both solar energy input and water availability: when they are both high, species richness is high; a high level of just one of these does not necessarily correlate with species richness -species richness will increase will a lot of solar radiation because it can support more individuals and extinction rates are lower when there are more individuals in the community, so species richness tends to be higher as well

What is the relationship between species composition and net primary productivity?

-species richness and relative abundance both impact community function: if a community has only a handful of species, it will be largely defined by those species and an abundant species may have a disproportionate impact on the community -net primary productivity tends to be higher and less variable/more stable when species diversity increases -plant biomass increases as the number of species in a community increases -however, as more and more species enter the community, their marginal impact on plant biomass falls

What is the geographic area hypothesis?

-species richness is greater near the tropics because there are more suitable environments for species to live -standard world maps are based on the Mercator Projection, which greatly overstates the actual size of countries in the polar region and understates the size of other countries and may mislead you into thinking there is not more land area in the tropics, when the tropics actually make up 40% of the Earth's landmass

What are the general patterns of biodiversity?

-species richness tends to decline as you move farther away from the equator (this latitudinal gradient was first identified by German explorer Alexander von Humboldt) -species richness is very high at the equator, but declines exponentially as you move north or south away from it

What can disturbances lead to?

-succession, or changes in the composition of the community over time -researchers have studied primary succession on the Indonesian island of Krakatoa, where a volcanic eruption in 1883 covered the entire island with lava and virtually wiped out all plant and animal life, over time, various species colonized the island and succession still continues today

What are 2 reasons for the relationship between species richness and plant biomass?

-super species: when a community has a large number of species, it is more likely that one of those species will do very well and produce a lot of biomass -niche complementarity

When is assimilation energy low/high?

-tends to increase as you move up to higher trophic levels -is low between primary producers and primary consumers because plant biomass is often difficult to digest -for example, plants may contain indigestible structural materials like cellulose and lignin, so assimilation efficiencies are much lower for herbivores than for carnivores (can be as low as 20% for herbivores and as high as 80% for carnivores)

What is primary productivity?

-the amount of light that gets converted into chemical energy by autotrophs during a given period of time -provides the fuel for all life on Earth, so understanding primary productivity is very important for biologists and non-biologists

What is secondary production?

-the difference between assimilated energy and respiration and represents the generation of biomass by heterotrophic consumers -the energy not used for growth and to produce offspring is used for bodily process like movement, blood circulation, thermoregulation, and maintaining homeostasis

Does all light energy converted into chemical energy go toward growth and reproduction?

no, some of the energy goes toward respiration and maintenance of autotrophs

What is net primary productivity (NPP)?

refers to the total amount of the chemical energy at one trophic level that goes toward building biomass at the next trophic level

A forest community that has been destroyed by fire might be colonized by small lichens and annual plants that are well-adapted to survive in harsh conditions. Over time, those plants might be replaced by perennial plants and grasses. Eventually, shrubs, softwood trees and pines, and hardwood trees might increase in abundance in the community. This is an example of:

succession

What is community ecology?

the study of the distribution and abundance of co-existing species and the interactions among them, linked by things like predation, competition, and mutualism

What is species diversity?

-a function of both species richness and relative abundance: = f(species richness + relative abundance) -there is greater species diversity when there are more species and more equal abundance -can be quantitatively measured by the Shannon Index

What occurs in the disturbance of species?

-causes an environmental change that has the capacity to change species composition -examples: volcanic eruptions, landslides, wildfires, tree falls, grazing by animals, and human activities -can be large-scale devastation or relatively small

What is species turnover?

-refers to the repeated patterns of spatial and temporal change in the species composition of communities, including colonization by new species and extinction of existing species -impacts species composition, which changes due to extinction, colonization, disturbances, and climate change

What is gross primary productivity (GPP)?

-refers to the total amount of light energy converted to chemical energy through photosynthesis (6CO2 + 6H2O → C6H12O6 + 6O2, occurs through light and green plants) -equals net primary productivity + respiration

What is assimilation efficiency?

-a measure of an organism's ability to extract the energy out of its food and it depends on how digestible an organism's food is -the total amount of energy assimilated by the organism = the total amount of energy ingested minus the total amount of energy egested (passed through/excreted) because it cannot be assimilated

What is consumption efficiency?

-a measure of what proportion of production at one trophic level is consumed (ingested) at the next tropical level - = (consumed energy/net production energy from previous trophic level) x 100 -look at how much energy was actually consumed, out of all the energy available from the previous trophic level

What occurred in the New Guinea study, which helped to confirm the island equilibrium theory?

-a study of the islands surrounding New Guinea (off the north coast of Australia) reveals that species richness is higher on larger islands and on islands close to the New Guinea mainland -formed the initial basis for the island equilibrium model

What are efficiency measures?

-an ecological community is like a machine that converts inputs into outputs -efficiency measures tell you how much you get out of the machine per unit that you put into the machine -efficiency measures are like miles-per-gallon ratings for cars, you put gasoline in and get miles out, and the miles-per-gallon rating tells you how many miles you get per gallon of gas

What is the history hypothesis?

-areas near the equator have had longer to accommodate species diversity because they are unaffected by ice ages that wiped out many species on other areas (disturbances are less frequent in the tropics) -the ice ages put a huge ice sheet over many land masses north and south of the equator, which essentially reset these areas in terms of species diversity, so they are playing catch up in comparison to tropical areas

What are the assimilation efficiency and energy formulas?

-assimilated energy= ingested - egested energy -assimilation efficiency= (assimilated energy/ingested energy) x 100 or (ingested - egested energy)/ingested energy x 100 -assimilation efficiency is simply the ratio of assimilated energy to ingested energy -ex. when a lynx eats a rabbit whole, it is ingesting energy, but some of the rabbit, like the bones, cannot be digested and will be egested in the lynx's feces

What is the island equilibrium model, developed by Robert H. MacArthur and Edward O. Wilson in the 1960s?

-attempted to conceptualize how species richness is determined for an island -based on a theoretical island, but can be applied to other ecosystems that can be thought of as ecological islands (or habitat islands), such as a lake or a mountain peak -proposed species richness on islands depends on distance from the mainland and island size, which affect colonization and extinction on the island -species richness is greater on islands closer to the mainland and on islands that are larger

What is a major type of disturbance that can change species composition, as shown in areas along the US-Mexico border and the Great Barrier Reef?

-climate change, which can be determined by examining fossilized pack rat middens (pack rats store pieces of vegetation in middens that can preserve material for up to 50,000 years) -researchers studying the areas along the US-Mexico border have found that what is currently desert grassland and shrubland used to be a pinon-juniper woodland, which is an example of an ecological transition to a distinctly different community -the change in composition of species in this area is likely due to climate change, these areas, now arid and hot, used to be far wetter -we also just experienced the third mass bleaching of the Great Barrier Reef in the last four years, which killed corals along the entire reef and was caused by an increase in ocean temperatures

How does the rate of colonization differ between an island far from the mainland and an island close to the mainland?

-colonization on an island far away from the mainland will be slower because it is harder for species on the mainland to reach an island farther away -this creates different equilibrium levels of species on islands far from and near the mainland: a near island will have higher species richness than a far island

Different kinds of organisms have differing levels of efficiency with regard to conversion of ingested food into new biomass. Although it varies from organism to organism, what are the general groupings of organisms for production efficiencies?

-ectotherms (like caterpillars): temperature conformers that do not regulate their body temperature using metabolic processes, use 65 to 80% of their total energy they consume for maintenance, leaving production efficiency of 10 to 50% -endotherms (like squirrels): aka homeotherms, temperature regulators, regulate their body temperatures using metabolic processes and use 85 to 95% of total energy consumed for homeostatic maintenance, leaving production efficiency of only about 1 to 5%, they are so inefficient because they are regulators and it takes a lot of energy to maintain a constant temperature

What is the flow of energy and nutrients in ecosystems?

-energy tends to flow through systems, whereas nutrients tend to cycle within them -energy tends to be lost as heat throughout the cycle between biota and the abiotic, so energy input is constantly required -the energy that plants convert to chemical energy comes from the Sun

What are the important implications for the inefficiencies in energy flow across trophic levels?

-the inefficiencies have implications for trophic level structure, biomass partitioning, and rates of herbivory and predation in an ecosystem -results in the traditional biomass pyramid that puts higher trophic levels on top (tertiary consumers) and the more abundant primary producers on the bottom as the standing crop biomass/total dry weight of organisms decreases from primary producers to tertiary consumers -for example, the amount of energy from the lowest trophic level that is available for biomass at higher tropic levels decreases as more levels are added, so you will not see an ecosystem with a large number of trophic levels and this is why there are fewer apex predators than organisms at the bottom of the food pyramid

What does it mean for the average efficiency from trophic level to trophic level to be approximately 10%?

-the third trophic level consists only of about 1% of net primary production -this is a major limit on the number of trophic levels that can exist in an ecosystem and most ecosystems have no more than 3 or 4 trophic levels -some people argue that humans should eat plants rather than animals to be more efficient by preventing significant energy loss that occurs as energy makes its way to higher trophic levels

How are gross primary productivity, net primary productivity, and respiration fluxes?

-they are rates with time dimensions -NPP is not the standing crop that exists on the earth at any time, NPP is the net biomass produced per unit time

What did Professor David Tilman and his associates discover about niche complementarity in the experiment at the University of Minnesota?

-they fenced off and cleared 32 different plots of land and introduced between 1 and 32 species to the land -they found that plant biomass increased as they added more species, but there came a point at which adding more species only had a slight impact on plant biomass -then, they introduced plants of between 1 and 5 functional groups (groups of plants that filled the same niche in their environments) and found that plant biomass increases as more functional groups are added, up to a point -the number of functional groups, and not the number of species in each functional group, that matters, which suggests the increase in plant biomass is best explained by niche complementarity and community output depends on fulfilling all of the complementary niches in the community

How have controlled tests by E.O. Wilson and Dan Simberloff helped to confirm the island equilibrium theory?

-they isolated several areas of mangrove with scaffolding and tents and then used a chemical to kill all of the arthropods in the areas -the mangrove islands were different distances from the mainland -they monitored the rate at which arthropods recolonized the island over the next 2 years and found that recolonization was fastest for the islands closer to the mainland

What occurs in niche complementarity?

-when a community has a large number of species, it is more likely those species will fill all of the available niches and exploit all of the community's resources -species-rich areas of land have the most plant functional groups, which can adjust to different environments (example: legumes are a functional group that can fix atmospheric nitrogen)

A caterpillar, an ectotherm, obtains 1,000 joules of energy by chewing leaves. Of this energy, 380 J is used to fuel metabolic processes, 500 J is lost in feces, and 120 J is converted to insect biomass. The production efficiency is:

120/1,000= 12%

If only 50% of rabbits are eaten by foxes, the consumption efficiency of foxes is ______. In terrestrial systems, consumption efficiency for herbivores is limited by the fact that much of the primary producers' biomass is __________.

50%, inedible (like wood)

a group of populations of different species that co-occur in the same geographic area

biological community -example: a species of butterfly, their host plants, and their bird predators living in the same area

refers to the diversity of species and which species exist in a community

community structure -is a function of species richness and relative abundance

What are the 3 subcategories of efficiency that ecological efficiency depends on?

consumption, assimilation, and production efficiency