Mate limitation in an estuarine population of copepods

Abstract

We determined the probability of mating as a function of population density in the estuarine copepod Acartia hudsonica by combining experimental measurements with a simple model. Pairs of unmated copepods were confined in containers of various volumes to simulate variable population density, and experiments were run for 8, 16, and 24 h. Mating frequencies indicated that males search for females at an effective search volume rate of 0.34 6 0.15 L h 21 or 8.2 6 3.5 L d 21 and that males become ready to mate only after ,15 h exposure to the females. We applied these parameters in a simple population model to determine the critical density for zero population growth. With high egg production, zero mortality, and residence time of 60 d, the critical density for A. hudsonica was 0.01 m 23 , at the low end of the range of observed population densities. Critical densities for less favorable conditions were well within the range of observed population densities, even allowing for the effects of aggregation. Thus, mate limitation in sexually reproducing organisms, or Allee effects, can cause negative density dependence in growth rate of these populations at low but realistic population densities. We applied these results to the introduction of exotic zooplankton via ships' ballast water under various scenarios of initial dilution in harbors and subsequent conditions for reproduction and survival. Inocula resulting from the discharge of postexchange ballast water were often high enough to establish new resident populations.

Mating success and its consequences for population growth in an estuarine copepod

“…Increasing detection range increases the volume search rate, i.e. the volume searched by males for females per unit time (Kiørboe 2007), which, in turn, reduces the population density needed to prevent mate limitation (Choi & Kimmerer 2008).In the present study, we determined the volume search rate for males of the calanoid copepod Eurytemora affinis and assessed the consequences of this rate for population recovery from low abundance. E. affinis (~1 mm total length) is a dominant species in many temperate estuaries, usually inhabiting lowsalinity areas, and is often associated with the maximum turbidity zone (e.g.…”

“…This is acceptable because we were concerned with dynamics only at low population levels. Other assumptions of this model are discussed by Choi & Kimmerer (2008).We applied this model to the Eurytemora affinis population in the San Francisco Estuary. Sex ratio was set at 1:1 (F f = 0.5).…”

“…We also assume that males become ready to mate over some time period and that some males may never be able to mate. The model and its additional assumptions were developed for a similar study of mating in Acartia hudsonica (Choi & Kimmerer 2008) 377: 183-191, 2009 We used the mating model with the experimental data to estimate the effective volume search rate V s . 'Effective' here refers to searches that result in mating and the production of nauplii.…”

“…The copepods were maintained at constant temperature (15°C) and ambient salinity (2 to 5), under artificial light for 8 h d . Throughout all experiments, we observed behavior of the copepods microscopically before, during, and after mating, and used only copepods that appeared to behave normally.The experimental design was based on previous such experiments with Acartia hudsonica (Choi & Kimmerer 2008) and results of ancillary experiments (next section). We incubated pairs of unmated copepods for 2, 4, or 8 h in containers of 6 capacities from 0.03 l to 16 l, and for 4 or 8 h in 32 l containers.…”

The effect of mating behavior and temperature variation on the critical population density of a freshwater copepod

“…Below this threshold, mate limitation is expected to result in a negative population growth rate. Mate limitation has been hypothesized to explain observed minimum population densities in other copepod species (Kiørboe 2006;Choi and Kimmerer 2008) and has been shown to contribute to the failure of H. shoshone populations to reestablish after fish disappearance (Sarnelle and Knapp 2004;Kramer et al 2008).…”