Helen A. Snyder

Defenses of the Florida Apple Snail Pomacea Paludosa

1. Pomacea paludosa exhibits a variety of defenses against predation, including aposematic eggs and dropoff-burial responses to odors of turtles, odors of crushed conspecific snails, and mechanical disturbance. 2. The conspicuous pinkish-white eggs are laid out of the water and hatch after several weeks incubation. Distastefulness is strong at first but disappears by hatching time. After hatching, snails are apparently tasty food items for a great variety of predators. The brightly colored eggs of other species of Pomacea may also be aposematic, though we have direct evidence for unpalatability in only one other species, Pomacea dolioides. 3. The self-burial alarm responses to turtle odors and intraspecific juices appear identical in form but are not identical in ontogeny. Response to intraspecific juice is not present on hatching, develops gradually over the first few weeks of free existence, and continues throughout the life of the snail. Burial responses to turtle odors are present in snails prior to the normal hatching date and continue for varying lengths of time after hatching. Response to Sternotherus minor odor continues until snails are about 3 grams in weight; response to Chelydra serpentina odor continues until snails are at least 20 grams in weight. Ontogeny of response to other turtle odors has not yet been investigated, though young Pomacea paludosa have been reactive to odors of all turtles tested to date. 4. The ontogenies of response to Sternotherus minor and Chelydra serpentina odors correlate closely with the abilities of adults of these turtles to eat snails. Adult Sternotherus minor in the laboratory have been unable to eat snails much larger than about 3 grams in weight, while an adult Chelydra serpentina has eaten snails over 20 grams in weight. Snails apparently discriminate between the odors of these two turtles on the basis of qualitative rather than quantitative differences in odor, and preliminary evidence suggests that snails do not discriminate between different-sized turtles within a species. 5. Intraspecific juice is potent in producing alarm in total darkness just as in the light. Response to turtle odors is almost completely inhibited by darkness, red light, or dim incandescent light. 6. Odors of most predators other than turtles produced no response in young Pomacea paludosa. Weak, inconsistent responses were seen to alligator and crocodile odors. 7. Both intraspecific juice and odor of Sternotherus minor are stable to 5 minutes boiling, but both lose potency after varying lengths of time in water solution. 8. Threshold to intraspecific juice is about .000,000,2 grams crude snail juice per liter. Threshold to Sternotherus minor odor can best be expressed as the amount of water a turtle can make alarming in a given length of time. For a 54 gram Sternotherus minor this figure was about 1500 liters in 10 minutes. 9. Attempts to detect active release of alarm substance in snails stimulated with alarm substance failed. 10. Other species of Pomacea also have analogous (homologous?) alarm reactions. Pomacea dolioides has a response to intraspecific juice similar in its ontogeny to the response of Pomacea paludosa to intraspecific juice, but Pomacea dolioides lacks a response to odor of Sternotherus minor. Pomacea glauca has no response to intraspecific juice but responds strongly to odor of Sternotherus minor during a short period of youth. Both Pomacea glauca and Pomacea dolioides also have alarm responses to mechanical disturbance.

Biology and Conservation of the California Condor

On Easter Sunday of 1987, the last California Condor (Gymnogyps californianus) known to exist in the wild was trapped for captive breeding, joining 26 others of his species at the San Diego and Los Angeles Zoos. A young male adult, he was a bird whose life had been followed closely for a number of years. His movements and interactions with other condors, his molting patterns and changes in coloration with age, as well as his pairing with an old female in late 1985, and his first breeding attempts in 1986 had all been documented in considerable detail. Like every other bird in the remnant population, he was known and had been studied as an individual. With his capture, an era of intensive investigations of condor natural history and ecology had come to a close.

Pheromone-mediated behaviour of Fasciolaria tulipa

Abstract Fasciolaria tulipa responds to the odour of conspecific snails with escape or capture behaviour. Escapes involve rapid gliding or leaping locomotion. Captures involve cannibalism or copulation. Successful captures for feeding occurred only when attackers were larger than their prey. In many captures for copulation the captor (male) was the smaller snail. The tendency to show capture behaviour increases with size, and snails are more likely to attack small snails than large ones. Size discrimination appears to depend, at least partially, on quantitative odour cues. The proportion of escapes versus captures is similar for both sexes though large males may posses a stronger tendency to capture large females than vice versa. Small snails repond to large ones as far away as 1·2 m upcurrent.

Trait-mediated trophic cascade creates enemy-free space for nesting hummingbirds

The presence of hawks at their nests alters the foraging height of predatory jays, creating a safe nesting area for hummingbirds. The indirect effects of predators on nonadjacent trophic levels, mediated through traits of intervening species, are collectively known as trait-mediated trophic cascades. Although birds are important predators in terrestrial ecosystems, clear examples of trait-mediated indirect effects involving bird predators have almost never been documented. Such indirect effects are important for structuring ecological communities and are likely to be negatively impacted by habitat fragmentation, climate change, and other factors that reduce abundance of top predators. We demonstrate that hummingbirds in Arizona realize increased breeding success when nesting in association with hawks. An enemy-free nesting space is created when jays, an important source of mortality for hummingbird nests, alter their foraging behavior in the presence of their hawk predators.