A new model for calculating the density of aqueous solutions of electrolytes has been developed. Parameters for 59 electrolytes were established on the basis of an extensive critical review of the ...published literature for solutions of one electrolyte in water, with over 10 700 points included. The average difference between the calculated and experimental density of solutions of water and one electrolyte is 0.10 kg m-3 with a standard deviation of 1.44 kg m-3. The model was validated by predicting the density of systems of two or more electrolytes in water. The average difference between experimental and calculated values for over 1600 points is 0.003 kg m-3 with a standard deviation of 1.39 kg m-3. The electrolytes studied are AlCl3, Al2(SO4)3, BaCl2, CaCl2, CdCl2, CdSO4, CoCl2, CoSO4, CrCl3, Cr2(SO4)3, CuCl2, CuSO4, FeCl2, FeSO4, FeCl3, Fe2(SO4)3, HCl, HCN, HNO3, H3PO4, H2SO4, KCl, K2CO3, KNO3, KOH, K2SO4, LiCl, Li2SO4, MgCl2, MgSO4, MnCl2, MnSO4, NaBr, NaCl, NaClO3, Na2CO3, NaF, NaHCO3, NaH2PO4, Na2HPO4, NaHSO3, NaI, Na2MoO4, NaNO2, NaNO3, NaOH, Na3PO4, Na2SO3, Na2S2O3, Na2SO4, NH3, NH4Cl, NH4NO3, (NH4)2SO4, NiCl2, NiSO4, SrCl2, ZnCl2, and ZnSO4.
The distance separating predator and prey when the predator begins to approach, starting distance, was recently shown to affect flight initiation distance in many bird species, raising questions ...about the effect's generality, variation with ecological factors, and economic basis. I studied the effect in two lizard species that forage by ambush and escape into nearby refuges. Monitoring costs during approach are absent because ambushers remain immobile while scanning for prey and predators. Risks are minimized because of the proximity to refuge. Flight initiation distance increased weakly with starting distance in Sceloporus virgatus Smith, 1938 significantly only at rapid approach speed. It was not significant in Urosaurus ornatus (Baird and Girard, 1852) at slow approach speed. Flight initiation distance is predicted to increase with starting distance, owing to monitoring costs and assessment by prey of greater risk during prolonged approaches. The significant effect in S. virgatus, which lacks monitoring costs, is the first indication that risk affects the relationship between starting distance and flight initiation distance. Conditions in which starting distance is important and its possible effects in earlier studies are discussed, as well as standardizing approaches and possible artifactual effects of starting distance.
Following autotomy of a body part to escape from a predator, prey may alter antipredatory strategies to compensate for the inability to use autotomy and impaired escape ability. Because prey that ...have been captured may increase their assessment of risk posed by a predator, effects of capture may have been attributed to autotomy. I conducted an experiment using three groups of striped plateau lizards (
Sceloporus virgatus
Smith, 1938): control, captured, and autotomized. Captured and autotomized lizards were less active on the day after autotomy than controls. Flight initiation distance and distance fled were greater in both experimental groups than in the control group, but did not differ between experimental groups. Flight initiation distance was greater in autotomized than in captured lizards only in males. No sex difference occurred for distance fled. Autotomized lizards entered refuges more than other groups. Escape strategy changed after autotomy to increased reliance on refuge and, in males, to increased flight initiation distance; behaviours that are appropriate to compensate for impaired escape ability. Decreased activity and increased distance fled might erroneously have been considered effects of autotomy, had effects of capture not been assessed. Predictions of escape theory that flight initiation distance and distance fled increase with predation risk were supported.
Ambush and active foraging are held to be discrete foraging modes having important theoretical consequences and evolutionary correlates, but foraging variables (number of movements per minute (MPM) ...and per cent time spent moving (PTM)) vary continuously. Whether foraging movements are unimodally or bimodally distributed is controversial. Foraging modes have been crucial for understanding taxonomic, morphological, ecological, and behavioural diversification of lizards. Extensive data for them are used to examine the modality-continuity controversy. MPM and PTM are lognormally distributed, confirming continuity and unimodality. By separating species into groups of ambush and active foragers, bivariate cluster analysis supports the view that lizards fall into active and ambush modes that may reflect adaptive peaks of joint MPM and PTM values. Phylogenetic analysis is needed to test relationships between variables. Although it has greatly advanced understanding of relationships between foraging and other variables, a two-mode paradigm is too simplistic. Modes defined solely by MPM and PTM may obscure differences in speed and search methods. Overlap between clusters might occur in nearly unstudied major taxa that forage differently. On the MPM×PTM plane connections among ambush, active, and saltatory (start-stop) foraging are apparent, suggesting that saltatory foragers may occur in lizards. Controversies about continuity, bimodality, and dichotomy of modes are resolved. Clusters represent common combinations of unimodally distributed MPM and PTM occupying limited regions of foraging space. Some species fall outside traditional modes, but examination of correlations between clusters and other variables remains a viable approach.
Escape behavior of the Mediterranean lizard Lacerta perspicillata was studied experimentally in a limestone quarry at Lithica on the island of Menorca, Balearic Islands, Spain. These lizards are ...exposed to avian predators while active on vertical rock faces. Simulated kestrel attacks using a cardboard model elicited escape responses from nearly all lizards approached. Methods of escape included entering a crevice, retreating over or around an edge, running behind a shrub growing against the rock surface, running behind a shrub and dropping to the ground ("bush to ground"), and retreating under or behind a rock isolated from a rock face. Most lizards fled directly to the closest available refuge or to alternative refuges only slightly farther away. Nevertheless, lizards that initially perched near crevices more frequently fled to other types of refuge than lizards that were initially near other refuges. The latter usually fled to the closest refuge. Lizards predominantly fled parallel to the ground or directly toward it (down) into a refuge regardless of the direction of attack (above, below, straight on). Direction of attack affected the type of refuge used. Lizards approached from above were more likely to flee to bush-ground or crevices than those approached from below or the same height. Straight-line retreat directly to a refuge appears to be the most viable escape strategy for these lizards when faced with attacks by avian predators, but the direction of attack may influence decisions based on risk.
Lizards use chemical cues to locate and identify prey and plant food, assess the nutritional quality of food, and detect plant toxins. Among insectivorous lizards, all actively foraging species ...studied respond strongly to prey chemicals sampled lingually, but ambush foragers do not. Much recent research has been devoted to assessing differential responses to food and nonfood chemicals (i.e., food-chemical discrimination) by omnivorous and herbivorous species and determining whether correlated evolution has occurred between plant diet and plant-chemical discrimination. We conducted experimental studies of food-chemical discrimination by two species of teiid lizards, the omnivorous Cnemidophorus murinus and the actively foraging insectivorous Ameiva ameiva. The omnivore distinguished both prey and plant chemicals from control substances. The insectivore exhibited prey-chemical, but not plant-chemical, discrimination, as indicated by tongue-flicking and biting. A comparative analysis using concentrated-changes tests showed that correlated evolution has occurred between plant consumption and plant-chemical discrimination in a major lizard taxon, Lacertiformes. These results extend and strengthen previous findings of similar correlated evolution to a new group and add to a growing database indicating that omnivorous lizards use chemical cues to assess both prey and plant foods.
AbstractEscape behaviour often differs between sexes, reproductive states and ages. Escape theory predicts that flight initiation distance (FID = predator–prey distance when escape begins) increases ...as predation risk and fitness increase, and decreases as cost of escaping increases. Similar predictions hold for distance fled and refuge entry, suggesting that age and sex differences in escape behaviour may occur when risk, fitness, and opportunity costs differ. I studied such differences in two lizard species and reviewed relevant literature on escape by lizards. In Sceloporus virgatus no difference occurred between sexes or female reproductive states in FID, distance fled, distance from refuge, or probability of entering refuge. In S. jarrovii juveniles had shorter FID and distance fled than adults; juveniles were closer than females to refuge, but this did not affect FID or distance fled. Juveniles were more likely than adults to be on rocks and use them as refuges. The literature review showed that sexual dimorphism in FID occurs in about 1/5 of species (male FID usually > female FID), but distance fled differed between sexes in only 1 of 21 species. Juveniles had shorter FID than adults in all of five species; the relationship between age and distance fled was highly variable. Reasons for patterns of age/sex differences are discussed. Because age and sex differences in these factors and escape strategy can alter multiple components affecting optimality, sometimes in opposite ways, these factors and escape strategy must be known to predict effects of age, sex and reproductive state on escape.
Sampling environmental chemicals to reveal prey and predators and to provide information about conspecifics is highly developed in lizards. Actively foraging lizards can discriminate between prey ...chemicals and control stimuli, but ambush foragers do not exhibit prey chemical discrimination. Recent experiments on a few species of herbivorous lizards have also demonstrated an ability to identify plant food chemicals. We studied chemosensory responses to chemicals from prey and palatable plants in two species of actively foraging, insectivorous lizards. Both the lacertid Takydromus sexlineatus and the teiid Cnemidophorus gularis exhibited strong responses to prey chemicals, but not to plant chemicals. These findings increase confidence in the relationship between prey chemical discrimination and foraging mode, which is based on data for very few species per family. They also provide data showing that actively foraging insectivores in two families do not respond strongly to plant cues. Such information is essential for eventual comparative studies of the relationship between plant diet and responses to food chemicals. The traditional method of presenting stimuli by using hand-held cotton swabs worked well for T. sexlineatus but could not be used for C. gularis due to repeated escape attempts. When stimuli were presented to C. gularis on ceramic tiles and no experimenter was visible, the lizards responded readily. Presentation of stimuli on tiles in the absence of a visible experimenter may be a valuable approach to study of food chemical discrimination by active foragers in which antipredatory behavior interferes with responses to swabs.PUBLICATION ABSTRACT
In the Kalahari desert the tree skink Mabuya striata sparsa occupies Acacia trees separated by areas of open sand. On a single day in austral spring, the effects of tree size and structural ...complexity, presence of colonial nests of weavers, and fallen limbs on lizard abundance, and of time of day and air temperature on numbers of lizards active, location on trees, ground, or ground cover, and occupation of sunny, shaded, or partially shaded sites were examined. Multiple regression showed that the numbers of adult and total lizards increased with tree size, amount of ground cover, and air temperature. Neither number and size of sociable weaver nests nor complexity of tree shape affected lizard abundance. Proportions of lizards on trees and ground did not vary with time of day; neither did height above ground among individuals on trees. The proportions of lizards fully exposed to the sun was higher early and late in the day than at midday, when more lizards occupied shaded sites.
Autotomy of expendable body parts is often a successful last-chance antipredatory defense for a variety of invertebrates and vertebrates, especially lizards. However, loss of a body part imposes ...costs and risks, some of which may be reduced by modifying subsequent behavior. I studied effects of experimentally induced autotomy of the tail in the keeled earless lizard (Holbrookia propinqua) on use of cover, escape behavior, activity, and feeding. Autotomized lizards stayed closer to plant cover than sham-autotomized lizards (having intact tails) when approached by an investigator simulating a predator. Autotomized males, but not females, fled further than sham-autotomized lizards. Autotomy did not affect the distance from an approaching predator when the lizards began to flee. After autotomy, the number of days on which lizards were active differed between sexes and lizards made fewer attempts to catch prey per unit time than lizards with intact tails. Tail loss did not affect the percentage of time spent moving. Staying closer to refuge, fleeing further after autotomy, and decreasing surface activity may compensate for decreased maximum escape speed or agility, and may reflect use of a greater margin of safety when the tail is unavailable for autotomy. Decrease in surface activity may be comparable to use of safer microhabitats reported for other lizards and damselflies subsequent to autotomy. Several possible reasons for the lower rate of feeding attempts by autotomized lizards are discussed.
