Wide home ranges for widely foraging lizards

Space usage by animals may be influenced by a range of factors. In this study we investigate whether foraging behaviour affects the home range size of lizards. Two distinct tactics of foraging have been recognized in predators: sit-and-wait foraging (SW) and active foraging (AF). Foraging activity level of a data set of lizard species, mainly compiled from literature, is compared with their home range sizes. Two opposite predictions can be made about foraging in connection with home range area: on the one hand, SW species may exhibit larger home ranges due to their mating system; on the other hand, AF species have higher metabolic energy and thus food requirements and can be expected to have larger home ranges that have to yield this food. This study shows that percentage of the time moving (as an index of foraging mode) correlates positively with home range, even after correcting for body mass, and these patterns remain when phylogenetic relationships are taken into account. We thus conclude that home range areas parallel activity levels in lizards.     

Dynamics of pre- and post-choice behaviour: rats approximate optimal strategy in a discrete-trial decision task

We simulate two types of environments to investigate how closely rats approximate optimal foraging. Rats initiated a trial where they chose between two spouts for sucrose, which was delivered at distinct probabilities. The discrete trial procedure used allowed us to observe the relationship between choice proportions, response latencies and obtained rewards. Our results show that rats approximate the optimal strategy across a range of environments that differ in the average probability of reward as well as the dynamics of the depletion-renewal cycle. We found that the constituent components of a single choice differentially reflect environmental contingencies. Post-choice behaviour, measured as the duration of time rats spent licking at the spouts on unrewarded trials, was the most sensitive index of environmental variables, adjusting most rapidly to changes in the environment. These findings have implications for the role of confidence in choice outcomes for guiding future choices.     

Relationships between sclerophylly,leaf biomechanical properties and leaf anatomy in some Australian heath and forest species

ABSTRACT

A previous study of 19 south-east Australian heath and forest species with a range of leaf textures showed that they varied considerably in leaf biomechanical properties. By using an index of sclerophylly derived from botanists' rankings (botanists' sclerophylly index, BSI) we determined that leaves considered by botanists to be sclerophyllous generally had both high strength and work to fracture (particularly in punching and tearing tests), both at the level of leaf and per unit leaf thickness. In the current study we have shown that leaves from the same species also varied considerably in leaf specific mass (46–251 g m^-2), neutral detergent fibre concentration (20–59% on a dry weight basis) and in leaf anatomy. Multiple regression indicated a very strong correlation between BSI and the first two components of a principal components analysis (PCA) of leaf anatomy (R ² = 0.91). In addition, there was strong correlation between the first component of a PCA of the mechanical properties (correlated with BSI) and the two axes derived from anatomical characteristics (R ² = 0.66). The anatomical properties contributing most to the significant component axes were thickness of palisade mesophyll and upper cuticle (axis 1) and percentage fibre (neutral detergent fibre) and lower epidermis thickness (axis 2). However, whether these relationships are causal, or reflect correlations with characteristics not measured in this study, such as vascularization and sclerification, is not clear. At a finer scale, however, there is evidence that there are various ways to be sclerophyllous, both in terms of anatomical and mechanical properties. This is illustrated by comparison of two of the sclerophyllous species, Eucalyptus baxteri and Banksia marginata.     

Effects of prey density,prey size and predator size on rates of feeding by an intertidal predatory gastropod Morula marginalba Blainville (Muricidae), on several species of prey

As a prerequisite for models of foraging behaviour of the whelk, Morula marginalba Blainville (Muricidae), the effects of variation in density of prey on the rate of feeding of the predator were examined in field conditions for three coexisting species of prey. Densities of prey used were those at which the prey, two limpets and a barnacle, occurred naturally in the rocky intertidal habitat.Large limpets, Cellana tramoserica (Sowerby) can resist attacks by predatory gastropods by raising the mantle over the outside of the shell. These experiments showed that no C. tramoserica were killed by Morula marginalba even at very great densities and with no alternative prey present. For the small limpet Patelloida latistrigata (Angas), one of the whelk's most highly preferred prey, juveniles were eaten 1.4 times as fast as adults. Fitting the random predator equation gave greater attack coefficients and shorter handling times for juvenile than adult limpets.Sizes of both predator and prey affected rates of eating barnacles, Tesseropora rosea (Krauss), but not in a simple way. Whelks of 15-mm aperture length ate adult barnacles 4.2 times faster than did 12-mm whelks, but there was no significant difference in the rates at which the two sizes of snail ate juvenile barnacles.Rates of feeding on T. rosea and Patelloida latistrigata increased significantly with prey density. These results form a basis for including the density of prey in models of spatial dispersion of the predatory gastropod Morula marginalba.     

Leaf size modifies support biomass distribution among stems, petioles and mid-ribs in temperate plants

The implications of extensive variation in leaf size for biomass distribution between physiological and support tissues and for overall leaf physiological activity are poorly understood. Here, we tested the hypotheses that increases in leaf size result in enhanced whole-plant support investments, especially in compound-leaved species, and that accumulation of support tissues reduces average leaf nitrogen (N) content per unit dry mass (N(M)), a proxy for photosynthetic capacity. Leaf biomass partitioning among the lamina, mid-rib and petiole, and whole-plant investments in leaf support (within-leaf and stem) were studied in 33 simple-leaved and 11 compound-leaved species. Support investments in mid-ribs and petioles increased with leaf size similarly in simple leaves and leaflets of compound leaves, but the overall support mass fraction within leaves was larger in compound-leaved species as a result of prominent rachises. Within-leaf and within-plant support mass investments were negatively correlated. Therefore, the total plant support fraction was independent of leaf size and lamina dissection. Because of the lower N(M) of support biomass, the difference in N(M) between the entire leaf and the photosynthetic lamina increased with leaf size. We conclude that whole-plant support costs are weakly size-dependent, but accumulation of support structures within the leaf decreases whole-leaf average N(M), potentially reducing the integrated photosynthetic activity of larger leaves.     

The influence of prey size and abundance, and individual phenotype on prey choice by the three-spined stickleback, Gasterosteus aculeatm L.

Prey selection behaviour of three-spined sticklebacks, Gasterosteus aculeatus L., was studied in two experiments. Where possible, the experimental apparatus satisfied the assumptions of the simplest optimal diet model (the basic prey model); prey were presented sequentially, the fish could not search for and handle prey at the same time, and net energy gain, handling time and encounter rate were fixed. Experiment 1 presented fish with a range of Asellus sizes so that pursuit ( p ) and handling ( h ) time could be related to prey size. Published energy values of Asellus together with pursuit and handling times were used to calculate E /( p+h ) for Asellus measuring 3,4,5,6,7 and 9 mm. Pursuit times did not differ with prey size but handling times did. E /( p+h ) was very variable particularly at the larger prey sizes. Experiment 2 presented fish with two sequences of prey differing in the encounter rate with the most profitable prey sizes. Fish did not select the diet predicted by the basic prey model tending to always ignore the largest prey even when net energy gain would have been maximized by including them in the diet. Further analysis showed that the probability of a prey size being taken was a function of prey size, fish stomach fullness and encounter rate. It is concluded that the basic prey model is too simple to capture the behaviour of the fish. One of its main faults is that the changing state of the fish through the feeding bout is ignored.