Nonsynchronous Spatial Overlap of Lizards in Patchy Habitats
TL;DR: The first observation may be related to the first in the following way: nonsynchronous spatial overlap could dictate relatively great resource overlap for species coinhabiting patchy or edge areas, requiring great differences between the species in prey size in addition to those in climatic habitat.
Abstract: Sympatric native Anolis species with similar structural habitats but contrasting climatic habitats are closer in head and body size on species—rich than on depauperate islands. In two localities, sympatric Anolis species with differential occurrences in sun or shade sought lower, more shaded perches during midday, resulting in partly nonsynchronous utilization of the vegetation by the two species. The second observation may be related to the first in the following way: nonsynchronous spatial overlap could dictate relatively great resource overlap for species coinhabiting patchy or edge areas, requiring great differences between the species in prey size in addition to those in climatic habitat. The extent of such overlap on small depauperate islands could be greater if these contained a greater proportion of patchy or edge habitats (with respect to insolation), or if climatic preferences were broader and more overlapping than on large, species—rich islands. In each locality, the relatively more shade—inhab...
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Cites background from "Nonsynchronous Spatial Overlap of L..."
...The simplest overlap measures are species association (considering presence and absence in samples only) as an analog of the Jaccard or Sorensen index indices given below, "percentage co-occurrence," SA = 2Mc/(Mh + Mi) (Agrell I945, Iversen I954, Whittaker & Fairbanks I958), and species correlation (comparing species importance values in samples) as an analog of percentage similarity, M M SC = min (phj, pij) = I -0.5 ph -p j1= j1= (Whittaker & Fairbanks I958, Schoener 1970, Price I971, Colwell & Futuyma I97I)....
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...…(Agrell I945, Iversen I954, Whittaker & Fairbanks I958), and species correlation (comparing species importance values in samples) as an analog of percentage similarity, M M SC = min (phj, pij) = I -0.5 ph -p j1= j1= (Whittaker & Fairbanks I958, Schoener 1970, Price I971, Colwell & Futuyma I97I)....
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TL;DR: To conclude with a list of questions appropriate for studies of resource partitioning, questions this article has related to the theory in a preliminary way.
Abstract: To understand resource partitioning, essentially a community phenomenon, we require a holistic theory that draws upon models at the individual and population level. Yet some investigators are still content mainly to document differences between species, a procedure of only limited interest. Therefore, it may be useful to conclude with a list of questions appropriate for studies of resource partitioning, questions this article has related to the theory in a preliminary way. 1) What is the mechanism of competition? What is the relative importance of predation? Are differences likely to be caused by pressures toward reproductive isolation? 2) Are niches (utilizations) regularly spaced along a single dimension? 3) How many dimensions are important, and is there a tendency for more dimensions to be added as species number increases? 4) Is dimensional separation complementary? 5) Which dimensions are utilized, how do they rank in importance, and why? How do particular dimensions change in rank as species nuimber increases? 6) What is the relation of dimensional separation to difference in phenotypic indicators? To what extent does the functional relation of phenotype to resource characteristics constrain partitioning? 7) What is the distance between mean position of niches, what is the niche standard deviation, and what is the ratio of the two? What is the niche shape?
3,626 citations
TL;DR: Throughout, emphasis will be placed on strategic aspects of feeding rather than on what Holling (75) has called "tactics," and possible answers to the first problem may be given to the second problem.
Abstract: Natural history is replete with observations on feeding, yet only recently have investigators begun to treat feeding as a device whose performance as measured in net energy yield/feeding time or some other units assumed commensurate with fitness-may be maximized by natural selection (44, 1 13, 135, 156, 181) . The primary task of a theory of feeding strategies is to specify for a given animal that complex of behavior and morphology best suited to gather food energy in a particular environment. The task is one, therefore, of optimization, and like all optimization problems, it may be tri sected: 1. Choosing a currency: What is to be maximized or minimized? 2. Choosing the appropriate cost-benefit functions: What is the mathematical form of the set of expressions with the currency as the dependent variable? 3. Solving for the optimum: What computational technique best finds ex trema of the cost-benefit function? In this review, most of the following section is devoted to possible answers to the first problem. Then four key aspects of feeding strategies will be considered: (a) the optimal diet, (b) the optimal foraging space, (c) the optimal foraging period, and (d) the optimal foraging-group size. For each, possible cost-benefit formulations will be discussed and compared, and predictions derived from these will be matched with data from the literature on feeding. Because the third problem is an aspect of applied mathematics, it will be mostly ignored. Throughout, emphasis will be placed on strategic aspects of feeding rather than on what Holling (75) has called "tactics."
3,356 citations
TL;DR: The topic here is the structure of lizard communities in this somewhat loose sense of the word (perhaps assemblage would be a more accurate description), with emphasis on the niche relationships among such sympatric sets of lizard species, especially as they affect the numbers of species that coexist within lizard communities.
Abstract: Strictly speaking, a community is composed of all the organisms that live together in a particular habitat. Community structure concerns all the various ways in which the members of such a community relate to and interact with one another, as well as community-level properties that emerge from these interactions, such as trophic structure, energy flow, species diversity, relative abundance, and community stabil ity. In practice, ecologists are usually unable to study entire communities, but instead interest is often focused on some convenient and tractable subset (usually taxonomic) of a particular community or series of communities. Thus one reads about plant communities, fish communities, bird communities, and so on. My topic here is the structure of lizard communities in this somewhat loose sense of the word (perhaps assemblage would be a more accurate description); my emphasis is on the niche relationships among such sympatric sets of lizard species, especially as they affect the numbers of species that coexist within lizard communities (species den sity). So defined, the simplest (and perhaps least interesting) lizard communities would be those that contain but a single species, as, for instance, northern populations of Eumeces msciatus. At the other extreme, probably the most complex lizard commu nities are those of the Australian sandridge deserts where as many as 40 different species occur in sympatry (20). Usually species densities of sympatric lizards vary from about 4 or 5 species to perhaps as many as 20. Lizard communities in arid regions are generally richer in species than those in wetter areas; therefore, because almost all ecological studies of entire saurofaunas have been in deserts (l8, 20, 25), this paper emphasizes the structure of desert lizard communities. As such, I review mostly my own work. Other studies on lizard communities in nondesert habitats are, however, cited where appropriate. Historical factors such as degree of isolation and available biotic stocks (particu larly the species pools of potential competitors and predators) have profoundly shaped lizard communities. Thus one reason the Australian deserts support such very rich lizard communities may be that competition with, and perhaps predation pressures from, snakes, birds, and mammals are reduced on that continent (20).
2,406 citations
TL;DR: Lentic freshwater habitats in temperate regions exist along a gradient from small ephemeral ponds to large permanent lakes, and fitness tradeoffs associated with a few critical traits of individuals often form the basis for species turnover along the gradient.
Abstract: ▪ Abstract Lentic freshwater habitats in temperate regions exist along a gradient from small ephemeral ponds to large permanent lakes. This environmental continuum is a useful axis for understanding how attributes of individuals ultimately generate structure at the level of the community. Community structure across the gradient is determined by both (a) physical factors, such as pond drying and winter anoxia, that limit the potential breadth of species distributions, and (b) biotic effects mediated by ecological interactions, principally predation, that determine the realized success of species. Fitness tradeoffs associated with a few critical traits of individuals often form the basis for species turnover along the gradient. Among species that inhabit temporary ponds, distributions are often constrained because traits that enhance developmental rate and competitive ability also increase susceptibility to predators. In permanent ponds, changes in the composition of major predators over the gradient limit ...
1,450 citations
Cites methods from "Nonsynchronous Spatial Overlap of L..."
...To briefly illustrate the degree of change in community structure across the predator transition, we used published surveys to calculate average community similarity [using species relative abundance and an index of overlap (140)] between the two community types relative to the average similarity within community types....
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References
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TL;DR: A graphical method is discussed which allows a specification of the optimal diet of a predator in terms of the net amount of energy gained from a capture of prey as compared to the energy expended in searching for the prey.
Abstract: A graphical method is discussed which allows a specification of the optimal diet of a predator in terms of the net amount of energy gained from a capture of prey as compared to the energy expended in searching for the prey. The method allows several predictions about changes in the degree of specialization of the diet as the numbers of different prey organisms change. For example, a more productive environment should lead to more restricted diet in numbers of different species eaten. In a patchy environment, however, this will not apply to predators that spend most of their time searching. Moreover, larger patches are used in a more specialized way than smaller patches.
4,132 citations
"Nonsynchronous Spatial Overlap of L..." refers methods in this paper
...As such, it supports the "compression" hypothesis of MacArthur and Pianka (1966), elaborated in MacArthur and Wilson (1967), that an early consequence of the coming together of two species should be that "the variety of occupied habitats (or more correctly the space searched) should shrink, or at…...
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TL;DR: The total number of species is proportional to the total range of the environment divided by the niche breadth of the species, which is reduced by unequal abundance of resources but increased by adding to the dimensionality of the niche.
Abstract: 1. There is a limit to the similarity (and hence to the number) of competing species which can coexist. The total number of species is proportional to the total range of the environment divided by the niche breadth of the species. The number is reduced by unequal abundance of resources but increased by adding to the dimensionality of the niche. Niche breadth is increased with increased environmental uncertainty and with decreased productivity. 2. There is a different evolutionary limit, L, to the similarity of two coexisting species such that a) If two species are more similar than L, a third intermediate species will converge toward the nearer of the pair. b) If two species are more different than L, a third intermediate species will diverge from either toward a phenotype intermediate between the two.
3,946 citations
"Nonsynchronous Spatial Overlap of L..." refers background in this paper
...Of special value in the latter type of analyses are the particularization and measurement of the kinds of resource overlap (Kohn 1966, Horn 1966, MacArthur and Levins 1967)....
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TL;DR: The address of the president of a society, founded largely to further the study of evolution, at the close of the year that marks the centenary of Darwin and Wallace's initial presentation of the theory of natural selection.
3,717 citations
TL;DR: In this article, the authors discuss two kinds of failure to make the best use of x2 tests which I have observed from time to time in reading reports of biological research, and propose a number of methods for strengthening or supplementing the most common uses of the ordinary x2 test.
Abstract: Since the x2 tests of goodness of fit and of association in contingency tables are presented in many courses on statistical methods for beginners in the subject, it is not surprising that x2 has become one of the most commonly-used techniques, even by scientists who profess only a smattering of knowledge of statistics. It is also not surprising that the technique is sometimes misused, e.g. by calculating x2 from data that are not frequencies or by errors in counting the number of degrees of freedom. A good catalogue of mistakes of this kind has been given by Lewis and Burke (1). In this paper I want to discuss two kinds of failure to make the best use of x2 tests which I have observed from time to time in reading reports of biological research. The first arises because x2 tests, as has often been pointed out, are not directed against any specific alternative to the null hypothesis. In the computation of x2, the deviations (fi mi) between observed and expected frequencies are squared, divided by mi in order to equalize the variances (approximately), and added. No attempt is made to detect any particular pattern of deviations (fi mi) that may hold if the null hypothesis is false. One consequence is that the usual x2 tests are often insensitive, and do not indicate significant results when the null hypothesis is actually false. Some forethought about the kind of alternative hypothesis that is likely to hold may lead to alternative tests that are more powerful and appropriate. Further, when the ordinary x2 test does give a significant result, it does not direct attention to the way in which the null hypothesis disagrees with the data, although the pattern of deviations may be informative and suggestive for future research. The remedy here is to supplement the ordinary test by additional tests that help to reveal the significant type of deviation. In this paper a number of methods for strengthening or supplementing the most common uses of the ordinary x2 test will be presented and illustrated by numerical examples. The principal devices are as follows:
3,351 citations
"Nonsynchronous Spatial Overlap of L..." refers background or methods in this paper
...More specifically, if the totals of the number of observations in the individual tables are different by a ratio of more than 2 to 1, or the proportions of the observations in the two categories being compared fall outside the range 0.20-0.80, the method is not very suitable (Cochran 1954)....
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...If that is suspected to be the case, it is not recommended that the data all be lumped (Cochran 1954)....
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