Ruth E. Buskirk

The Natural Selection of Sexual Cannibalism

Sexual cannibalism, in which a male is eaten by his mate following copulation, is expected to convey a selective advantage to the male under certain conditions. As shown quantitatively in our model the phenomenon is expected when (1) a male can mate only a few times in his lifetime and (2) the cannibalism significantly increases the number and/or viability of eggs fertilized by his own sperm. The expected number of male matings appears to be the more important of these two conditions. The few available observations of sexual cannibalism in several species of arthropods agree qualitatively with the predictions of our model. The same parameters of the model also explain why sexual cannibalism is generally rare among vertebrates. Phenomena selecting for sexual cannibalism appear more closely related to paternal investment strategies than to ecological factors associated with other forms of cannibalism. Because few field studies of invertebrates have followed the mating history of marked males, we cannot test our model quantitatively with existing data. We suggest specific field observations which would provide quantitative estimates of the expected number of male matings. In addition we describe possible laboratory experiments which would give more precise measurements of the increase in fecundity of the cannibalized male.

Omnivory and Utilization of Food Resources by Chacma Baboons, Papio ursinus

Chacma baboon omnivory is an adaptation to reduce intraspecific and interspecific competition for food resources. When available, animal matter was the most preferred food, and alternative foods were ignored. Fruits and seeds were second choice and leafy vegetation was least preferred. Under most circumstances the troop social structure and the morphology of baboons reduces predation risk and the need for watchfulness. Baboons consequently can spend long intervals processing food, thus enabling them to circumvent the antiherbivory adaptations of many plants. This enables baboons to utilize resources unavailable to some interspecific competitors.

A trap-building predator exhibits different tactics for different aspects of foraging behaviour

Abstract Orb-web spiders present a particularly informative system for the analysis of foraging strategies because foraging investment, as measured by web size and foraging bout length, is temporally disjunct from decisions determining diet breadth. This decoupling allows simultaneous consideration of both aspects of foraging behaviour. The orb-weaving spider, Nephila clavipes , exhibits variation in foraging bout length, orb-web structure and diet that may reflect different strategic responses to different rates of prey capture. Within each of three study populations, orb size increased with spider size. Spiders built larger orbs relative to spider size during times of decreased mean rate of prey capture. Similarly, decreased mean prey capture corresponded to longer foraging bouts among populations. In contrast, diet breadth did not increase with decreasing mean prey capture. The changes in foraging investment follow the predictions of optimal foraging behaviour, whereas the changes in patterns of prey rejection can be explained as physiological limitations such as water requirements during the dry season.

Transmission and attenuation of vibration in orb spider webs

Abstract Numerous observations indicate that orb spiders react to web-borne vibrations during prey capture, courtship and the rearing of young, but there have been very few analyses of the physics of spider webs undergoing vibration. Using measured or estimated physical properties for spiders and webs from previous literature, we have developed equations that model the response of web-spider systems to signals at various frequencies. Our results indicate that resonance phenomena do not affect signal transmission in most orb webs in the frequency range of sound produced by the wingbeats of most flying insects (about 50–1000 Hz). Above 1000 Hz, individual strands in a web could resonate, but attenuation should prevent significant transmission, at least for transverse vibrations. For signals with frequencies below about 30 Hz, resonant vibrations of the spider or other massive objects within the web could affect transmission significantly.

Evidence that biological activity affects Ocean Bottom Seismograph recordings

Brief and impulsive signals of uncertain origin appear regularly on records from Ocean Bottom Seismographs (OBS) of several institutions. These signals have been recorded on nearly all deployments of the Texas OBS, including sites at depths greater than 7000 m. At some sites, they account for over 90% of the events recorded. They are of short duration (usually 0.5–4.0 s) and have a characteristic frequency (usually in the range of 4–18 Hz) that differs from site to site. When networks of OBS instruments are deployed, the signals are not recorded simultaneously by different instruments. Neither the frequency content nor the distribution of durations of these signals is similar to what is observed for known earthquake events.We present evidence suggesting that the signals are of biological origin, perhaps caused by animals touching the OBS units. (1) The distribution of these signals on instruments deployed at depths shallower than 1000 m shows a 24 h periodicity, while there is a 24 h periodic pattern on instruments deployed at sites deeper than 1000 m (where there is no visible light). (2) The frequency of occurrence of signals is similar to the vertical distribution of biomass in the oceans, i.e., they appear most frequently on OBS instruments deployed at very shallow depths. (3) Biological material has been found attached to several OBS units upon recovery.

Magnetic Remanence and Response to Magnetic Fields in Crustacea

Crustacea comprise a major portion of the diversity and biomass of marine fauna, yet their biology is little known in comparison to their terrestrial counterparts, the insects. These marine arthropods display oriented movements in their habitat as well as timing of behavior with respect to environmental stimuli. There have been very few studies, however, of either the effects of magnetic fields on Crustacea or the magnetic fields generated by living Crustacea. In this chapter, we report the first measures of significant magnetic remanence in Crustacea, we relate this biological magnetism to that described in other animals, and we discuss its possible significance in the life history of shrimp and barnacles.