Energy Flow in an Ecosystem (With Diagram)
For example, gravitational potential energy is associated with the gravitational force acting on object's mass; elastic potential energy with the elastic force. Overland runoff converts potential into kinetic energy more visibly than mass .. surface roughness of the ecosystem through the KM term in the stress equation. The amount of kinetic energy of an object is dependent upon two variables, one being the mass of the object, the other being the speed or the.
Although this limited set of interviews cannot represent all physical-science faculty members, it did uncover several differences in how science faculty members teach about energy and matter at the introductory level. Our findings are divided into three sections: Definitions and presentations of energy and matter in introductory physics, chemistry, and biology textbooks The textbooks' treatments of matter differed markedly from those of energy. Of the 10 textbooks we surveyed, 8 defined energy, and all of them included energy in the index.
Only four textbooks defined matter, and five included matter in the index table 2.
Three biology texts included the idea that energy can promote or cause change, and two one biology, one chemistry described energy in relation to the movement of heat.
We see several problems here. First, several words e. Furthermore, abstract terms such as work may confuse students.
For example, will introductory-level students understand the work done when a concentration gradient is maintained across a cell membrane or when amino acids condense to form proteins Wood-Robinson ? The contexts in which energy appeared in the textbook indices varied. All of the textbooks addressed various forms of energy e. In a widely-cited paper he suggested that population energy use could be estimated as the product of population density and mean metabolic rate i. The energetic equivalence rule has also garnered widespread attention since it provides a quantifiable prediction for a point of great interest in ecology — the distribution of energy among populations in a community — on the basis of a relatively easily-measured variable, body size.
This energetic equivalence rule, and its emphasis on three-quarter-power scaling with body mass, has provided the theoretical foundation for explaining a range of ecological patterns, from population growth  to community structure  to global biodiversity patterns . Later authors  expanded on this idea, noting that population energy use would also be independent of body size wherever both scaling exponents were exactly inversely correlated.
This energetic equivalence hypothesis predicts that inverse scaling relationships of population density and metabolic rate are widespread, and that population energy use by different species is broadly independent of body size in ecological communities . While the energetic equivalence hypothesis has been supported in some studies this hypothesis is only one possible expectation for energy use within ecological communities .
Other studies have proposed and provided evidence in support of alternative hypotheses: Thus, despite intense interest in size-energy hypotheses, and despite their potential importance for understanding community structure and dynamics, past studies have produced conflicting results and the influence of body size on energy use in ecological communities remains unclear.
Potential energy - Wikipedia
In addition, size-energy hypotheses have been controversial because they are often disconnected from the proposed mechanism underlying these hypotheses — namely, that size-energy relationships result from energetic tradeoffs due to resource competition among organisms of different body sizes in a community  but see .
This mechanism implies that size-energy hypotheses apply only in certain ecological contexts — namely those where all species can directly compete for shared, limiting resources. Previous studies of size-energy hypotheses, however, have tended to examine large spatial scales by compiling data from many different communities around the globe e. Further, those studies that have examined the local scale have not controlled for resource availability e.
- Potential Energy
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- Energy Flow in an Ecosystem (With Diagram)
Inferences about size-energy hypotheses from large spatial scale or multi-resource studies should therefore be interpreted carefully. Size-energy hypotheses, and past tests of these hypotheses, have also been controversial on methodological grounds, in part due to a tendency to confound distinct scaling relationships in two primary ways. First, all previous studies have indirectly used size-density relationships, rather than size-energy relationships, to test size-energy hypotheses e.
However, recent study suggests that metabolic scaling exponents are highly variable and so a specific exponent cannot be assumed for all systems i. This approach also suffers from a lack of data on species-specific metabolic scaling exponents and is subject to the hidden non-linearity, propagation of error variances, and inherent imprecision of multiplying allometric relationships .
This practice is also circular, since in the analysis, body size serves both as the predictor variable M and as a means to calculate the response variable PEU ; results therefore will tend to be biased to suggest a positive correlation.
As a result, although size-density relationships are interesting in their own right and can provide insight into mechanisms underlying energy use, their utility for estimating the form of the size-energy relationships that are the focus of size-energy hypotheses or for providing a robust test of these hypotheses remains unclear . Second, two distinct approaches to evaluating size-energy hypotheses have emerged on the basis of the underlying assumptions for how energy use is regulated in ecological communities.
Competition for energy implies zero-sum dynamics where limited resources are allocated to individual organisms in the community  and thus increases in energy consumed from a shared, limiting resource by one individual are necessarily offset by equal and opposite decreases in energy consumed by other individuals.
Authors of studies on terrestrial animals have generally assumed that such competition for energy is regulated by competition among species populations in a community e. For the former assumption, population energy use PEU is used to evaluate the size-energy relationship, whereas for the latter assumption, a related but distinct variable — size class energy use SCEU — is used. Unlike PEU, which is calculated as the sum of the energy used by all individuals in a species population, SCEU is calculated as the sum of the energy used by all individuals in a given size class, regardless of species identity.
Because size classes may vary in the number of species they contain, and individuals of a single species may be distributed among multiple size classes, tests of size-energy hypotheses using each approach may provide differing results for the same community .
Size-Energy Relationships in Ecological Communities
Despite these differences, reviews of size-energy hypotheses have typically not distinguished between the population and size-class approaches, leading to confusion in the literature . Comparison of the two approaches in the same system could clarify underlying assumptions of how energy use is regulated in communities.
Such comparisons have been completed for size-density relationships in multi-trophic communities  see also  for discussionbut not for size-energy relationships.
Our goal in this project was to directly evaluate size-energy hypotheses while clarifying how results would differ with alternate methods and assumptions.
Size-Energy Relationships in Ecological Communities
We had three objectives in support of this goal. First, we sought to complete the first analyses of size-energy hypotheses to directly measure how energy use scales with body size. Specifically, we evaluated whether energy use is independent of body size, increases with body size, decreases with body size, or peaks at an intermediate body size. Second, we sought to evaluate the influence of indirect versus direct methods on conclusions about size-energy hypotheses. Specifically, we compared results of our novel direct method with those from the indirect method conventionally used to test size-energy hypotheses.