Life history patterns of a livebearing fish in contrasting environments

Abstract

The population dynamics and energy allocations of the Gila topminnow, a small livebearing fish, were studied in two contrasting environments, a spring run of constant characteristics and a fluctuating desert wash. Topminnows grew and matured in two basic patterns. First, many fish in both areas matured the year after their birth. Second, spring fish born early in the breeding season grew rapidly, bred within five months, and died by eight months of age. Although spring fish assimilated more energy, wash fish actually expended more calories for growth and reproduction, partly because of lower maintenance costs. Reproductive effort of long-lived spring fish varied with age between 3.1 and 6.5%; whereas efforts of short-lived spring and wash fish increased steadily with age to 5.2 and 9.8%, respectively. Although spring fish produced eggs of higher energy content, females in both areas varied their investment per offspring, apparently tracking seasonal changes in the availability of food for fry. When long-lived spring fish experienced food shortage, they allocated less energy to both growth and reproduction; in contrast, wash and short-lived spring fish under similar conditions reduced only their growth allocation. The reproductive mass in spring fish appeared to be limited by food availability, incompletely filled the abdominal space, and reflected no tradeoff between fecundity and investment per offspring. Reproduction by wash fish appeared to be limited by body space and was characterized by a tradeoff between fecundity and egg size.

Population dynamics of the Devils Hole pupfish

“…The alternate hypothesis predicts differential survivorship as follows: (a) individuals born early mature, spawn and subsequently die within one season (e.g., an individual born in March matures in May and spawns through September); and (b) those born late in the year mature towards the end or after the reproductive and peak productivity seasons, survive over the winter and spawn in the next reproductive season. Such a polymorphic life history pattern has been documented in the Gila topminnow, Poeciliopsis occidentalis, from Monkey Spring, Arizona (Constantz 1979).…”

Predation and life-history variation in Poecilia reliculata (Cyprinodontiformes: Poeciliidae)

“…A great deal of basic information has been accumulated on life-history variation in this group (e.g., Bellamy 1924, Constantz 1979, Endler 1980, Farr 1980, Reznick 1983, Stearns 1983, Trendall 1982. In particular, Reznick & Endler (1982) investigated differences in life-history characteristics among sets of natural populations of Trinidad guppies, Poecilia reticulata, exposed to differing types and intensities of predation.…”

About processes which cause the evolution of guilds and species

“…of its range and precocial to the south. Similarly, the life history pattern of Poeciliopsis occidentalis (Constantz 1979) clearly points to the existence of twin forms, as do data presented for other fishes (e.g. Fenderson 1964, Frost 1965, Rupp & Redmont 1966, Messieh 1976, Kobayasi 1976, Copeman & McAllister 1978, Bruce 1980, but see Stearns 1980).…”