摘要:

We consider the idea that foraging animals seek to achieve a certain threshold intake of food per day rather than maximising mean energy intake. Earlier experiments and theoretical work have shown that under these conditions animals should respond to variance in reward. We identify six possible sources of such variance and produce models for five of them (the sixth is already solved). These models describe (1) whether to feed in habitats possessing small or large prey, (2) whether to feed on clumped or dispersed prey, (3) which prey items to eat, (4) the effects of misidentification of prey selection, (5) whether to feed singly or join a flock and (6) when to move between patches when the travel time between them is variable. The results are often radically different from those of traditional models and we discuss their biological significance.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1987.tb00292.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

It is possible to interpret components of seed development in angiosperms from the perspective of parent‐offspring conflict (a special case of kin selection) or sexual selection. Available parent‐offspring conflict models predict the evolution of traits determining the outcome of competition among related individuals soliciting maternal resources. In such models, ‘selfishness’ may spread even if it reduces female fecundity and thus population mean fitness may decline. These models are limited, however, because most of them do not simultaneously consider selection among maternal genotypes varying in the tendency to respond to their offspring. Available sexual selection models, in contrast, do consider the joint evolution of polygenic male traits (influencing viability, mating success and fecundity) and female preferences (influencing the mating success of different male phenotypes). These models have shown that male traits may evolve that are non‐optimal with respect to viability. Only one recent sexual selection model explicitly incorporates direct fecundity selection upon females; this model concludes that fecundity will be maximized at equilibrium. Hence population mean fitness may decline due to reduced male viability but not due to diminished female fecundity. Available sexual selection models, however, are limited because they do not consider the effects of interactions among relatives.The assumptions and qualitative results of the two types of models are compared and discussed in the context of seed development. Differential allocation of maternal resources among genetically distinct developing seeds may be viewed from the perspective of either. Because the results of the available models of parent‐offspring conflict and sexual selection are not wholly consistent and because data confirming the genetic basis of maternal patterns of investment or differential male reproductive success are scant, it is not clear which set of conclusions is most appropriate to apply to plants. To achieve the generality towards which mathematical approaches aspire, new models concerning the evolution of traits influencing resource allocation in plants must incorporate the components of both parent‐offspring conflict and sex

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1987.tb00293.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Spider orb webs are dynamic, energy absorbing nets whose ability to intercept prey is dependent on both the mechnical properties of web design and the material properties of web silks. Variation in web designs reflects variation in spider web spinning behaviours and variation in web silks reflects variation in spider metabolic processes. Therefore, natural selection may affect web function (or prey capture) through two independent and alternative pathways. In this paper, I examine the ways in which architectural and material properties, singly and in concert, influence the ability of webs to absorb insect impact energy. These findings are evaluated in the context of the evolution of diverse aerial webs.Orb webs range along a continuum from high to low energy absorbing. No single feature of web architecture characterizes the amount of energy webs can absorb, but suites of characters indicate web function. In general, webs that intercept heavy and fast flying prey (high energy absorbing webs) are large, built by large spiders, suspended under high tension and characterized by a ratio of radii to spiral turns per web greater than one. In contrast, webs that intercept light and slow flying prey (low energy absorbing webs) are suspended under low tension, are small and are characterized by radial to spiral turn ratios that are less than one. The data suggest that for spiders building high energy absorbing webs, the orb architecture contributes much to web energy absorption. In contrast, for spiders that build low energy absorbing webs, orb architecture contributes little to enhance web energy absorption. Small or slow flying insects can be intercepted by web silks regardless of web design. Although there exists variation in the material properties of silk collected from high and low energy absorbing webs, only the diameter of web fibres varies predictably with silk energy absorption. Web fibre diameter and hence the amount of energy absorbed by web silks is an isometric function of spider size.The significance of these results lies in the apparent absence of selective advantage of orb architecture to low energy absorbing webs and the evolutionary trend to small spiders that build them. Where high energy absorption is not an exacting feature of web design, web architecture should not be tightly constrained to the orb. Assuming the primitive araneoid web design is the orb web, I propose that the evolution of alternative web building behaviours is a consequence of the general, phyletic trend to small size among araneoids. Araneoids that build webs of other than orb designs are able to use new habitats and resources not available to their ancestors.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1987.tb00294.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Xeropicta vestalis, a polymorphic helicelline as regards its shell‐banding pattern, has shells that closely resemble those ofTheba pisana, a helicine. These resemblances are found mainly in Israel's coastal plain, where distribution of the two species overlaps to a certain extent, and it hardly ever occurs in Israel's hilly region whereT. pisanais missing. In the Jordan Valley however (whereT. pisanais missing also), someT. pisana‐like forms ofX. vestalismay occur. BecauseX. vestalisis smaller thanT. pisana, the resemblance refers mainly to juveniles and small adults of the latter, and less to large adults.We examined whether there are any interspecific relations between the frequencies of visually analogous morphs, in mixed populations. No such relations was found. Further, mixed populations are so unstable in time that the chances of building up any such relation is highly unlikely.It is difficult to accept that there are any interrelationships whatsoever (of apostatic selection as well as mimicry) betweenT. pisanaandX. vestalisas regards their shell banding polymorphism. The convergence between the two species appears to represent parallel, but not interspecific forces of natural select

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1987.tb00295.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Sexual reproduction is defined as the union of two haploid nuclei each derived from one of two different meioses. The implications of this definition for the interpretation of sexuality in coenocytes and homothallic haploids is discussed. The separation of the concept of the nuclear cycle from that of the life‐history is advocated, and a new terminology for the nuclear cycle is proposed. The distinction between the terms life‐cycle and life‐history is reite

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1987.tb00296.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY