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The composition of a spider population in terms of species and numbers is influenced by many environmental factors. Examples of faunal differences between simple, uniform habitats and those which are much more diverse are discussed. This paper examines the characteristics of populations in different habitat types, some stable and others subject to use which causes disturbance. When adequate and accurate samples are taken of spider populations in a defined habitat it is usual to find a few Abundant species, a large number of Scarce, and a third category which is classified as Frequent. The species—numbers relationship can then be illustrated by calculating the proportion of the total population represented in each of the three groups. When graphed, an L-shaped curve is produced, which varies according to the structure and environmental conditions of the habitat, as well as to the sampling method used. A number of examples are described, and possible ecological interpretations are discussed.
Several of the cues generally used by orb-weaving spiders to guide sticky spiral placement are missing when the spider lays the first loop of sticky spiral in an orb. This study combines behavioural observations and web measurements to suggest that two species of spiders use the distance between the outer loop of temporary spiral and the frame line to guide placement of the first loop. The correlation between these two variables occurred, however, only in a context in which spiders contacted the frame—when the outer loop of temporary spiral was near the frame. The correlation was absent when the temporary spiral-frame distance was large, and spiders generally failed to contact the frame line. The cue used to produce the correlation is thus probably sensed when the spider contacts the frame line while laying the first loop.
Prey selection is essential for individual fitness; therefore, it would be expected that a predator would select prey of a higher rank (energy/time) when exposed to prey of differing quality. In this paper, we compare the feeding effectiveness (biomass consumed/time) of Megaphobema mesomelas (O. P.-Cambridge, 1892) in captivity, and the preference between two prey types: beetles and crickets. Spiders are more effective when feeding on crickets. The heavy exoskeleton of beetles increases prey-handling time in order to access a relatively smaller amount of edible tissue. Effectiveness also increases with spider and prey size (mass), with larger spiders feeding more effectively on larger prey. Spiders show a strong preference for feeding upon crickets over beetles when both prey types are offered at the same time.
Although orb web construction behaviour is relatively well studied, there are few studies of the mechanisms with which behavioural decisions are executed, in terms of where the spider grasps lines and attaches them to each other. Video analyses were used here to show that the distance from the previous sticky loop at which the araneid spider Micrathena duodecimspinosa gripped the radius with her leg oIV during sticky spiral construction varied according to the spider's position in her web with respect to both gravity and the edge of the web. This grasping site, in turn, was correlated with the site on the radius where the spider attached the sticky line. The spacing between loops of sticky spiral, a functionally important aspect of orb design, was thus determined in part, though not completely, by the site at which leg oIV grasped the radius at the moment of attachment.
Inclusions in amber and copal provide us with a unique insight into terrestrial palaeocommunities because they represent a palaeobiocoenosis: a naturally co-occurring group of organisms that perished at they same point in time and in the same place. We report the first (sub)fossilized example of a spider population, preserved in Colombian copal, which has been dated back as far as 1736 /- 35 years. The specimen contains 26 spiders belonging to the Euryopis/Emertonella genus complex (Theridiidae). Such subfossils in copal provide exciting new research opportunities in molecular palaeobiology for investigating changes in genetic variation within a group at the threshold of ecological and evolutionary timescales.