Burns Carolyn W
Max-Planck Institute for Limnology, Postfach 165, D-24302, Plön, Germany.
Oecologia. 1995 Feb;101(2):234-244. doi: 10.1007/BF00317289.
The effects of daphniid crowding on juvenile growth rate, length at first reproduction, clutch size and egg size of four species of Daphnia were compared with the effects of food level. Juvenile Daphnia were grown to primipary in a flow-through system in water conditioned by different densities of the same, or another, species. At high ambient food levels, water from Daphnia that had been crowded at densities ≥150 l depressed growth rate and lowered body size and clutch size of D. hyalina and D. galeata; effects on the same traits of D. magna and D. pulicaria were variable (stimulation, depression, or no effect). D. hyalina and D. galeata responded to gradients of increasing daphniid density (0-300 l) by altering egg mass, somatic mass and clutch size to maintain a relatively constant reproductive investment; egg mass increased with crowding and then decreased in a pattern consistent with Glazier's (1992) hypothetical model of changes in offspring size in relation to food quantity and maternal demand. Effects of crowding by conspecifics were indistinguishable from those of other species. This study, which uncouples the effect of crowding per se from ambient resource depletion, shows that chemical substances released by high densities of Daphnia can cause changes in life-history traits comparable to those that occur in response to low food levels.
将水蚤的拥挤效应与食物水平的影响相比较，研究了水蚤拥挤对四种水蚤幼体生长率、首次繁殖时的体长、产卵量和卵大小的影响。将幼体水蚤置于流通系统中，在由相同或另一种水蚤的不同密度调节的水中培养至首次繁殖。在高环境食物水平下，来自密度≥150只/升的拥挤水蚤的水会降低透明溞和盔形溞的生长率，减小其体型和产卵量；对大型溞和蚤状溞相同性状的影响则各不相同（刺激、抑制或无影响）。透明溞和盔形溞通过改变卵质量、体细胞质量和产卵量来响应水蚤密度增加的梯度（0-300只/升），以维持相对恒定的繁殖投入；卵质量随着拥挤程度增加而增加，然后下降，其模式与格拉齐尔（1992年）关于后代大小与食物量和母体需求关系变化的假设模型一致。同种个体拥挤的影响与其他物种的影响无法区分。这项研究将拥挤本身的影响与环境资源消耗的影响分离开来，表明高密度水蚤释放的化学物质可导致生活史特征发生变化，这些变化与低食物水平引起的变化相当。
