Sympatric predators

In summary, growing a deep body in response to sympatric predators appears to reduce the need for behavioral alarm behavior (Pettersson etal, 2000). 

FIGURE 12.2 Responses of beavers to predator chemicals applied to aspen sticks. Activity periods were consecutive 5 days of experiment in two areas in New York and the percentages of sticks consumed is the mean of several replications of the experiment. All treated sticks were punctured to improve the uptake of chemicals intact sticks were untreated (A), punctured but not treated ( ), punctured and treated with the solvent methanol ( ) (the three controls), or treated with extracts from other animals. Treatments that inhibited consumption most were excrement extracts from lynx (+) and coyote ( ... ), both sympatric predators (lynx now extirpated). Beavers accepted most readily the three control sets. Other chemicals were from otter (o), wolf ( - ), lion ( ). (From Engelhart and Miiller-Schwarze,... 

In black-tailed deer, Odocoikus hemionus columbianus, fecal odors of sympatric predators (coyote, C. latrans, and mountain lion, Fdis concolor) in vials next to food pellets inhibited feeding, while those of allopatric predators (lion, Fdis leo, snow leopard, Uncia uncia) do not, or very little (Miiller-Schwarze, 1972 Fig. 12.3). Note that mammals discriminate between the odors of sym- and allopatric predators, while fish and rattlesnakes do not (pp. 359 and 364). Free-ranging adult female wapiti, Cervus elaphus canadensis, respond to the odors of dog urine, and cougar and wolf feces (presented as water slurry) with increased heart rates. It was concluded that the main effect of predator odors may be for assessing the risk of predation (Chabot etal, 1996). 

Three- or two-sample choices work best. A predator odor can be juxtaposed to a nonpredator odor and a nonscented control, making for a three-way choice test. In a second version of the experiment, one can differentiate the predator odor by comparing odors of a ground and an arboreal predator. Finally, odors of a native (sympatric) predator can be compared with those of an exotic (allopatric) one (Miiller-Schwarze 1972). These test whether sulfur compounds common to many carnivores are alarming - as suggested by Nolte et al. (1994) - or whether more specific stimuli are at work. 

Levels of predation risk influence the strength of the alarm response in the laboratory, female Trinidadian guppies, Poecilia reticulata, from a population with much predation, shoaled, dashed, and froze more in response to skin extract from sympatric females than did females from a population that experienced less predation (Brown and Godin, 1999). 

Free-ranging North American beaver. Castor canadensis, feed less on experimental aspen sticks that have been treated with extracts from predator excrement or urine. Odors from the sympatric coyote and river otter, and extirpated lynx, were most effective, while those from allopatric lion and extirpated wolf odor were less active. However, these response differences between species were small (Fig. 12.2 Engelhart and Muller-Schwarze 1995). 

Deer mice, P. maniculatus, on an island (Moresby Island, Gulf Islands, British Columbia) that now lacks their usual predator, the short-tailed weasel, M. erminea, still respond to its odor. However, they only show the more delayed and prolonged stress-type, opioid-sensitive behavior. By contrast, this island population has lost its fear and flight responses, which are benzodiazepine sensitive and more immediate. Mainland deer mice that are sympatric with weasels show both types of response (Kavaliers, 1990). 

The pteropod Clione antarctica, a pelagic mollusc, produces the polyketide pteroenone (Structure 7.69).53 Pteroenone is distasteful to sympatric fish.54 C. antarctica are subject to capture by the amphipod Hyperiella dilatata, which holds them in place on its dorsum and is similarly avoided by the same fish predators (see Section III.A, below). 

Such alarm cues are t) ically released following mechanical damage to prey, as would occur during a predation attempt. When detected by nearby conspecifics and some sympatric heterospecifics, these alarm cues can elicit dramatic, short-term increases in species typical antipredator behaviours (Chivers and Smith, 1998). Recent studies by Mirza and Chivers (2001, 2002, 2003) and Chivers et al. (2002) have shown that individuals responding to chemical alarm cues gain significant survival benefits associated with an increase in antipredator behaviour. 

Comparison of the pheromone systems of closely related species, has revealed that the attraction and the pheromone-receptor interaction found between them correlates with the degree of relatedness (Lanier and Wood, 1975 Priesner, 1979a, b). However, such a cross attraction could be disadvantageous for related species living in the same area, and under such circumstances an additional interspecific mechanism - interruption - is found which serves to maintain the isolation between sympatric species (Birch, Chapter 12). Thus, one species may produce an additional pheromone compound which interrupts the attraction of the other species. Chemical compounds which function as pheromones may also serve as cues for predators, parasitoids and prey (Vincent, Chapter 8). In these cases the predator or parasites have developed capabilities for recognizing the pheromones of their prey or host insects. Predators may also produce the attractants of their prey (Weaver, 1978 Eberhard, 1977). Conversely, some insect species have developed defensive compounds which are avoided by both insect and vertebrate predators, (cf. Eisner, 1970 Blum, 1978 Huheey, Chapter 10). Finally, during... 

---