02646nas a2200301   4500008004100000020001400041245009300055210006900148260001200217300001600229490000700245520185300252653001702105653001202122653002302134653002302157653001502180653001302195653001402208653001302222653002102235653001602256653001302272653000902285653000902294100001702303856002402320       2004                        eng d  a0012-965800aTrait-initiated indirect effects due to changes in consumption rates in simple food webs0 aTraitinitiated indirect effects due to changes in consumption ra  c2004///  a1029 - 10380 v853 aThis article explores the potential indirect effects due to changes in consumption-related traits of a focal prey species in each of two simple food webs. The systems considered are: one predator exploiting two independent prey, and one predator exploiting two prey that use a common limiting resource. In each system, the indirect effect of a change in a consumption-related parameter of one prey species on the population density of the other prey is determined. When prey only share a predator, the change in one prey’s density produced by a change in the other prey’s vulnerability to the predator is determined by whether or not that second prey is initially overexploited; i.e., whether its exploiter’s intake decreases with an increase in the attack rate. Increases in the vulnerability of an overexploited prey decrease the predator population and thereby indirectly increase the population size of the second prey. Increases in the vulnerability of a prey that is not overexploited have the opposite effects on both the predator and second prey populations. Both of these outcomes can be reversed by strong direct density dependence in the predator, provided the predator exhibits satiation. In the food web with a shared food and a shared resource, increases in predator vulnerability of the more vulnerable prey species always increase the population size of the more resistant prey species. However, increases in the vulnerability of the more resistant prey can either increase or decrease the population size of the more vulnerable prey species. When the more resistant prey becomes better at capturing the resource, the less resistant may either increase or decrease. Overexploitation also explains these outcomes. General principles for understanding the consequences of changes in vulnerabilities or attack rates are discussed10aCONSEQUENCES10aDENSITY10aDENSITY DEPENDENCE10aDENSITY-DEPENDENCE10aDEPENDENCE10afood web10afood webs10aFOOD-WEB10aindirect effects10aPOPULATIONS10aPREDATOR10aPREY10aSIZE1 aAbrams, P.A.  uISI:00022076660001401624nas a2200193   4500008004100000020001400041245011100055210006900166260001200235300001400247490000700261520104300268653000901311653002201320653002201342100001601364700002601380856002401406       2008                        eng d  a1461-023X00aThe tropics: cradle, museum or casino? A dynamic null model for latitudinal gradients of species diversity0 atropics cradle museum or casino A dynamic null model for latitud  c2008///  a653 - 6630 v113 aSeveral ecological and evolutionary hypotheses have been proposed to explain the latitudinal diversity gradient (LDG), but a general model for this conspicuous pattern remains elusive. Mid-domain effect (MDE) models generate gradients of species diversity by randomly placing the geographic ranges of species in one- or two-dimensional spaces, thus excluding both evolutionary processes and the effect of contemporary climate. Traditional MDE models are statistical and static because they determine the size of ranges either randomly or based on empirical frequency distributions. Here we present a simple dynamic null model for the LDG that simulates stochastic processes of range shifts, extinction and speciation. The model predicts higher species diversity and higher extinction and speciation rates in the tropics, and a strong influence of range movements in shaping the LDG. These null expectations should be taken into consideration in studies aimed at understanding the many factors that generate latitudinal diversity gradients10aSIZE10aspecies diversity10aSPECIES-DIVERSITY1 aArita, H.T.1 aVazquez-Dominguez, E.  uISI:00025637690000102080nas a2200253   4500008004100000020001400041245013900055210006900194260001200263300001400275490000800289520135100297653001601648653001301664653002601677653001701703653001401720653001401734653000901748653001101757100001701768700001701785856002401802       2007                        eng d  a0003-014700aDoes competition between resources change the competition between their consumers to mutualism? Variations on two themes by Vandermeer0 aDoes competition between resources change the competition betwee  c2007///  a744 - 7570 v1703 aHow does competition between resources affect the interaction between consumer species that share those resources? Existing theory suggests that high resource competition can lead to mutualism. However, this is based on an analysis that need only apply near equilibrium, and experimental demonstrations of such mutualism are rare. Two alternative approaches to measuring food web mutualism are examined here. These are based on the population level effects of adding or removing a consumer species or on the amount of additional mortality that can be applied to one consumer without excluding it. Both measures suggest that mutualism is likely to be confined to two situations: when overlap in resource use by the consumers is very low and when the consumers are inefficient users of their resources. Competition between resources is also likely to increase the occurrence and magnitude of "hypercompetition" between consumers, where the reduction in population size caused by the introduced consumer is greater than that caused by a consumer that is identical to the resident species. Competition between resources can also increase the negative interaction between consumers by destabilizing the dynamics of the system. Such destabilization can cause negative indirect interactions between specialist consumers having no overlap in resource use10aCOMPETITION10aDYNAMICS10aindirect interactions10ainteractions10aMORTALITY10aMUTUALISM10aSIZE10atheory1 aAbrams, P.A.1 aNakajima, M.  uISI:00024998150000902585nas a2200229   4500008004100000020001400041245009500055210006900150260001200219300001600231490000700247520197100254653001302225653001702238653001402255653001302269653001402282653000902296653000902305100001702314856002402331       2008                        eng d  a0012-965800aMeasuring the impact of dynamic antipredator traits on predator-prey-resource interactions0 aMeasuring the impact of dynamic antipredator traits on predatorp  c2008///  a1640 - 16490 v893 aThis article analyzes the limitations of the most widely used method for quantifying the impact of dynamic antipredator traits on food chain dynamics and discusses alternative approaches. The standard method for a predator-prey-resource chain estimates the effects of the prey’s defensive behavior by comparing population densities or fitness measures in a ’’predator cue’’ treatment to those in a no-predator treatment. This design has been interpreted as providing a measure of the ’’nonconsumptive effect’’ of the predator on the prey and the ’’trait-mediated indirect effect’’ of the predator on the resource. Other approaches involve measurements of the impact of the behavior in the presence of functional predators. The questions addressed here are: (1) How consistent are the results of different approaches? (2) How time-dependent are their results? (3) How well do they correspond to theoretical measures of effect size? (4) How useful are the measurements in understanding system dynamics? A model of a tritrophic system in which the prey species adjusts a defensive trait adaptively is used to evaluate the experimental designs. Measures of changes in prey fitness or population density in a cue treatment generally include offsetting effects of the cost of the behavior and the benefit of more resources. This means that the sign of the effect, as well as its magnitude, may change depending on when the experiment is terminated. Because predation is not present in the cue treatment, few conclusions can be drawn about the impact of the behavior on population densities or fitness of the prey in a natural setting with predators. Cue experiments often do not accurately separate trait-mediated from density-mediated effects on the resource. Most scalar measures of effects are sensitive to experimental duration and initial densities. Use of a wider range of experimental designs to measure trait-related effects is called for10aDYNAMICS10ainteractions10apredation10aPREDATOR10apredators10aPREY10aSIZE1 aAbrams, P.A.  uISI:00025654030001702293nas a2200241   4500008004100000020001400041245008200055210006900137260001200206300001400218490000700232520167300239653001701912653001301929653001401942653001301956653001401969653000901983653000901992653000902001100001702010856002402027       2008                        eng d  a1522-061300aMeasuring the population-level consequences of predator-induced prey movement0 aMeasuring the populationlevel consequences of predatorinduced pr  c2008///  a333 - 3500 v103 aQuestions: (1) What impact does adaptive movement away from areas of high predation risk have on the dynamics of a prey species and its resource? (2) What can experiments that introduce or remove predator cues tell us about the answer to question (1)? Mathematical methods: These questions are addressed using a two-patch meta-community model in which predators and/or their cues are incorporated into a system consisting of a prey species and its resource. Predators and/or cues may be introduced to one or both patches. Key assumptions: Prey species move adaptively to maximize their instantaneous rate of increase, but also make some random movement. Predators move randomly or do not move. Resources seldom or never move between patches. Consumer species have saturating functional responses. Conclusions: (1) Adaptive movement can stabilize or destabilize the dynamics of the tri-trophic system. (2) Monitoring densities in a single patch may give a misleading indication of the global change in densities. (3) Adaptive prey movement in response to predator cues may increase or decrease prey density. (4) Predator introduction may cause an increase or decrease in the size of the prey population. (5) Short-term experiments with local measurements may greatly overestimate the impact of predators on prey and the behavioural component of that impact. (6) The dynamics and interspecific effects in a system with predators and adaptive avoidance by prey cannot in general be deduced from separate experiments with cues alone and with predators in the absence of the cues. (7) Conclusions from recent empirical studies should be reassessed in light of these results10aCONSEQUENCES10aDYNAMICS10apredation10aPREDATOR10apredators10aPREY10aRISK10aSIZE1 aAbrams, P.A.  uISI:000256015000002