scispace - formally typeset
Search or ask a question
Author

N. Philip Ashmole

Bio: N. Philip Ashmole is an academic researcher from American Museum of Natural History. The author has contributed to research in topics: Paternal care & Predatory fish. The author has an hindex of 4, co-authored 5 publications receiving 311 citations.

Papers
More filters
Journal ArticleDOI
TL;DR: It is argued that the phenomenon of ecological segregation need not indicate the operation of competitive exclusion, and it is suggested that many natural habitats cannot be assumed to contain the greatest number of related species that could coexist there indefinitely if the opportunity to establish themselves arose.
Abstract: Collection and analysis of food samples permitted comparison of the diets of five species of terns that occur together on Christmas Island, Pacific Ocean. All the terns feed mainly while flying, catching fish and squid chased to the surface by predatory fish. Sterna fuscata and Anous stolidus, which are of equal size, catch prey of similar kinds and sizes, but S. fuscata can exploit feeding areas further from land, and is more numerous. Gygis alba and especially Anous tenuirostris are smaller and eat smaller prey. Gygis eats many fish and squid of kinds not important to A. tenuirostris, and may catch them at different times. Procelsterna cerulea, the smallest species, eats mainly fish larvae and tiny inveltebrates. The three most closely related species, A. stolidus, A. tenuirostris, and Procelsterna, differ mainly in size. The ratios of their weights are 3.8: 2.0: 1, but the ratios of the mean volumes of the largest 2 per cent of their fish prey are 30: ca. 7 : 1. The reasons for the discrepancy are discussed. The value of data on bill length, bill thickness, and body size in assessing the extent of competition for food among bird species is considered. It is argued that the phenomenon of ecological segregation need not indicate the operation of competitive exclusion, and it is suggested that many natural habitats cannot be assumed to contain the greatest number of related species that could coexist there indefinitely if the opportunity to establish themselves arose.

158 citations

Journal ArticleDOI
03 Apr 2008-Ibis
TL;DR: In this article, the authors investigated the role of social factors in maintaining breeding synchrony in sea-birds, and compared the diversity of the breeding regimes exhibited on Christmas Island with those found in the birds of Ascension Island and the Galapagos Archipelago.
Abstract: Summary Christmas Island, at 2° N, 157° W in the Central Pacific Ocean, supports 18 breeding species of sea-birds Data on the breeding seasons collected by the authors and other visitors to the island are analyzed in individual species accounts Population estimates are given, the distribution of each species on the island is outlined, and for some species information on the sexual and moult cycles of marked individuals is presented The Discussion concerns the ultimate and proximate factors controlling breeding seasons and the role of social factors in maintaining breeding synchrony in sea-birds, the diversity of the breeding regimes exhibited on Christmas Island (summary and analysis in Fig 2 and Table 5), and comparison of these regimes with those found in the birds of Ascension Island and the Galapagos Archipelago

47 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols used xiii 1.
Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

14,171 citations

Journal ArticleDOI
05 Jul 1974-Science
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

Journal ArticleDOI
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

Book
17 Mar 1996

1,701 citations

Journal ArticleDOI
TL;DR: Bat wing morphology is considered in relation to flight performance and flight behaviour to clarify the functional basis for eco-morphological correlations in flying animals, and adaptive trends in wing adaptations are predictably and closely paralleled by echolocation call structure.
Abstract: Bat wing morphology is considered in relation to flight performance and flight behaviour to clarify the functional basis for eco-morphological correlations in flying animals. Bivariate correlations are presented between wing dimensions and body mass for a range of bat families and feeding classes, and principal-components analysis is used to measure overall size, wing size and wing shape. The principal components representing wing size and wing shape (as opposed to overall size) are interpreted as being equivalent to wing loading and to aspect ratio. Relative length and area of the hand-wing or wingtip are determined independently of wing size, and are used to derive a wingtip shape index, which measures the degree of roundedness or pointedness of the wingtip. The optimal wing form for bats adapted for different modes of flight is predicted by means of mechanical and aerodynamic models. We identify and model aspects of performance likely to influence flight adaptation significantly; these include selective pressures for economic forward flight (low energy per unit time or per unit distance (equal to cost of transport)), for flight at high or low speeds, for hovering, and for turning. Turning performance is measured by two quantities: manoeuvrability, referring to the minimum space required for a turn at a given speed; and agility, relating to the rate at which a turn can be initiated. High flight speed correlates with high wing loading, good manoeuvrability is favoured by low wing loading, and turning agility should be associated with fast flight and with high wing loading. Other factors influencing wing adaptations, such as migration, flying with a foetus or young or carrying loads in flight (all of which favour large wing area), flight in cluttered environments (short wings) and modes of landing, are identified. The mechanical predictions are cast into a size-independent principal-components form, and are related to the morphology and the observed flight behaviour of different species and families of bats. In this way we provide a broadly based functional interpretation of the selective forces that influence wing morphology in bats. Measured flight speeds in bats permit testing of these predictions. Comparison of open-field free-flight speeds with morphology confirms that speed correlates with mass, wing loading and wingtip proportions as expected; there is no direct relation between speed and aspect ratio. Some adaptive trends in bat wing morphology are clear from this analysis. Insectivores hunt in a range of different ways, which are reflected in their morphology. Bats hawking high-flying insects have small, pointed wings which give good agility, high flight speeds and low cost of transport. Bats hunting for insects among vegetation, and perhaps gleaning, have very short and rounded wingtips, and often relatively short, broad wings, giving good manoeuvrability at low flight speeds. Many insectivorous species forage by `flycatching' (perching while seeking prey) and have somewhat similar morphology to gleaners. Insectivorous species foraging in more open habitats usually have slightly longer wings, and hence lower cost of transport. Piscivores forage over open stretches of water, and have very long wings giving low flight power and cost of transport, and unusually long, rounded tips for control and stability in flight. Carnivores must carry heavy loads, and thus have relatively large wing areas; their foraging strategies consist of perching, hunting and gleaning, and wing structure is similar to that of insectivorous species with similar behaviour. Perching and hovering nectarivores both have a relatively small wing area: this surprising result may result from environmental pressure for a short wingspan or from the advantage of high speed during commuting flights; the large wingtips of these bats are valuable for lift generation in slow flight. The relation between flight morphology (as an indicator of flight behaviour) and echolocation is considered. It is demonstrated that adaptive trends in wing adaptations are predictably and closely paralleled by echolocation call structure, owing to the joint constraints of flying and locating food in different ways. Pressures on flight morphology depend also on size, with most aspects of performance favouring smaller animals. Power rises rapidly as mass increases; in smaller bats the available energy margin is greater than in larger species, and they may have a more generalized repertoire of flight behaviour. Trophic pressures related to feeding strategy and behaviour are also important, and may restrict the size ranges of different feeding classes: insectivores and primary nectarivores must be relatively small, carnivores and frugivores somewhat larger. The relation of these results to bat community ecology is considered, as our predictions may be tested through comparisons between comparable, sympatric species. Our mechanical predictions apply to all bats and to all kinds of bat communities, but other factors (for example echolocation) may also contribute to specialization in feeding or behaviour, and species separation may not be determined solely by wing morphology or flight behaviour. None the less, we believe that our approach, of identifying functional correlates of bat flight behaviour and identifying these with morphological adaptations, clarifies the eco-morphological relationships of bats.

1,641 citations