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DFC PRocEmms - CONTRIBUTED PAPER
<br />with G. nobilis, G. heterochir and Poedlia young)
<br />with sample sizes of more than 50. In general, G.
<br />nobilis, G. heterochir and G. gaigei males ate more
<br />young that did males of G. afflnis, G. speciosa, and
<br />G. geiseri. Conversely, G. nobilis, G. heterochir and
<br />G. gaigei young had a higher survival rate than
<br />those of the other three species.
<br />Similarly, predation by females followed the
<br />same pattern as that reported previously (Table
<br />7). Survival of Paodha young exposed to G. afflnis
<br />females was lower than that of any Gambusia
<br />species. Predation by other species was similar,
<br />with most survival of G. a.,f finis young among the
<br />lowest. Predation on G. afflnis young by
<br />congeneric females was substantially higher than
<br />that of males. Congeneric predation on G. afflnis
<br />young was higher with G. geiseri, G. nobilis or G.
<br />gaigei females than using G. afinis, G. spedosa, or
<br />G. heterochir females. In this test, G. geiseri went
<br />from low to high and G. heterochir went from high
<br />to low in comparison with male predation. Again,
<br />survivorship with G. nobilis females was lowest in
<br />four of the six tests with sample sizes over 100.
<br />The exceptions were G. nobilis and G. gaigei
<br />young, where G. nobilis predation was second
<br />highest, and G. nobilis with G. heterochir young.
<br />Again, G. nobilis, G. heterochir and G. gaigei young
<br />had a higher survival rate than those of the other
<br />three species. Conspecific predation was highest
<br />by G. afflnis females (= cannibalism); G. heterochir
<br />and G. gaigei conspecific predation was also quite
<br />high.
<br />Extensive variation of survivorship occurred
<br />when G. afflnis young were exposed to female G.
<br />afflnis predation (Table 8). In two tests (Lost
<br />River and Big Bend), more than two-thirds of the
<br />young survived. In contrast, in seven tests (Bitter
<br />#3, Falcon, El Tigre, Fairy, Junction, Middle
<br />Creek, and Uncertain), survivorship was below
<br />10%. Survivorship with males as predators
<br />tended to be similar with the two high survivors
<br />having 79 and 88% survivorship and the six with
<br />low figures having 85, 76, 66, 73, 64, 77, and
<br />68% survivorship. Six of the seven survival
<br />percentages with male predators were lower than
<br />either of the two with high survivorship with
<br />female predators. In two other populations
<br />(Pecos and Clear Creek) where the survivorship
<br />with female predators had percentages above 50,
<br />the comparable male tests had survivorships of 81
<br />and 85%. Similarly, Big Bend and Junction
<br />females were tested with G. speciosa and G. geiseri
<br />young. In each instance, survivorship with Big
<br />Bend females was higher than those with Junction
<br />females (61 vs. 18% and 73 vs. 8%). These
<br />results remained consistent whether either of two
<br />sets of field-caught females or laboratory-raised
<br />females (from Big Bend) were used. There is a
<br />distinct difference in predation on newborns
<br />depending upon the population of adults used.
<br />Clearly, the choice of G. a-(finis stocks used for
<br />mosquito control would have great influence on
<br />average predation on young fishes. It is possible
<br />that G. afinis predation on other prey such as
<br />mosquitos may vary among populations equally.
<br />Such tests by mosquito control agencies are now
<br />mandated.
<br />The variation of predation by G. afsnis
<br />adults does not have a geographic or ecologic
<br />pattern. The two New Mexico populations are
<br />from the Bitter Lakes National Wildlife Refuge:
<br />one is in the low and the other in the high group.
<br />Lazy Pond is one kilometer from the Pecos River
<br />site. Survivorship with female predators differs
<br />by 43% and is significant at beyond the 0.00001
<br />level (xZ = 81). Survivorship based on individual
<br />tests is also significant beyond the 0.001 level.
<br />Too Much Pond is intermediate geographically
<br />and in predation rate.
<br />The four high-survival populations (Lost
<br />River - saline, stenothermal; Big Bend - low
<br />salinity, stenothermal, elevated temperature;
<br />Pecos - moderate salinity, eurythermal; Clear
<br />Creek - low salinity stenothermal) have little in
<br />common. The seven low survival populations
<br />(Bitter #3 - saline, eurythermal; Falcon -
<br />moderate salinity, eurythermal; El Tigre - saline,
<br />eurythermal; Fairy - low salinity, stenothermal;
<br />Middle Creek - low salinity, stenothermal;
<br />Uncertain - very low salinity, eurythermal) are
<br />equally variable. None of these environmental
<br />factors are associated with predation rates.
<br />Predation by female G. geised on G. afflnis
<br />young also varies substantially. All but one of the
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