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没有实验证据表明雏鸟阶段的局部竞争是密度依赖型鸟类窝卵数的驱动力。

No experimental evidence for local competition in the nestling phase as a driving force for density-dependent avian clutch size.

作者信息

Nicolaus Marion, Both Christiaan, Ubels Richard, Edelaar Pim, Tinbergen Joost M

机构信息

Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, The Netherlands.

出版信息

J Anim Ecol. 2009 Jul;78(4):828-38. doi: 10.1111/j.1365-2656.2009.01535.x. Epub 2009 Feb 26.

Abstract
  1. In birds, local competition for food between pairs during the nestling phase may affect nestling growth and survival. A decrease in clutch size with an increase in breeding density could be an adaptive response to this competition. To investigate whether breeding density causally affected the clutch size of great tits (Parus major), we manipulated breeding density in three out of eight study plots by increasing nest-box densities. We expected clutch size in these plots to be reduced compared to that in control plots. 2. We analysed both the effects of variation in annual mean density (between-year comparisons) and experimental density (within-year comparison between plots) on clutch size variation, the occurrence of second broods and nestling growth. We examined within-female variation in clutch size to determine whether individual responses explain the variation over years. 3. Over the 11 years, population breeding density increased (from 0.33 to 0.50 pairs ha(-1)) while clutch size and the occurrence of second broods decreased (respectively from 10.0 to 8.5 eggs and from 0.39 to 0.05), consistent with a negative density-dependent effect for the whole population. Nestling growth showed a declining but nonsignificant trend over years. 4. The decline in population clutch size over years was primarily explained by changes occurring within individuals rather than selective disappearance of individuals laying large clutches. 5. Within years, breeding density differed significantly between manipulated plots (0.16 pairs ha(-1) vs. 0.77 pairs ha(-1)) but clutch size, occurrence of second broods and nestling growth were not affected by the experimental treatment, resulting in a discrepancy between the effects of experimental and annual variation in density on reproduction. 6. We discuss two hypotheses that could explain this discrepancy: (i) the decline in breeding performance over time was not due to density, but resulted from other, unknown factors. (ii) Density did cause the decline in breeding performance, but this was not due to local competition in the nestling phase. Instead, we suggest that competition acting in a different phase (e.g. before egg laying or after fledgling) was responsible for the density effect on clutch size among years.
摘要
  1. 在鸟类中,雏鸟阶段成对个体间对食物的局部竞争可能会影响雏鸟的生长和存活。随着繁殖密度的增加窝卵数减少可能是对这种竞争的一种适应性反应。为了研究繁殖密度是否对大山雀(Parus major)的窝卵数有因果影响,我们通过增加巢箱密度,在八个研究地块中的三个地块上操纵繁殖密度。我们预期这些地块的窝卵数与对照地块相比会减少。2. 我们分析了年平均密度变化(年间比较)和实验密度(地块间的年内比较)对窝卵数变化、第二窝的出现以及雏鸟生长的影响。我们研究了雌鸟窝卵数的个体内变化,以确定个体反应是否能解释多年间的变化。3. 在这11年中,种群繁殖密度增加(从0.33对/公顷增至0.50对/公顷),而窝卵数和第二窝的出现减少(分别从10.0枚卵降至8.5枚卵,从0.39降至0.05),这与整个种群的负密度依赖效应一致。雏鸟生长多年来呈下降趋势,但不显著。4. 多年来种群窝卵数的下降主要是由个体内部发生的变化导致的,而非产大窝卵个体的选择性消失。5. 在同一年中,操纵地块的繁殖密度差异显著(0.16对/公顷对0.77对/公顷),但窝卵数、第二窝的出现以及雏鸟生长不受实验处理的影响,导致实验密度变化和年度密度变化对繁殖的影响存在差异。6. 我们讨论了两个可以解释这种差异的假设:(i)繁殖性能随时间的下降并非由于密度,而是由其他未知因素导致的。(ii)密度确实导致了繁殖性能的下降,但这并非由于雏鸟阶段的局部竞争。相反,我们认为在不同阶段(例如产卵前或 fledgling 后)起作用的竞争是多年间密度对窝卵数产生影响的原因。 (注:“fledgling”此处可能有误,推测原文可能是“fledging”,意为“离巢” )

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