Gorosito Irene L, Douglass Richard J
Departamento de Ecología Genética y Evolución Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires Buenos Aires Argentina.
Instituto de Ecología Genética y Evolución de Buenos Aires Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires Argentina.
Ecol Evol. 2017 Nov 15;7(24):11113-11123. doi: 10.1002/ece3.3598. eCollection 2017 Dec.
Small-mammal population densities can be regulated by bottom-up (food availability) and top-down (predation) forces. In 1993, an El Niño Southern Oscillation event was followed by a cluster of human hantavirus with pulmonary syndrome in the southwestern United States. An upward trophic cascade hypothesis was proposed as an explanation for the outbreak: Increased plant productivity as a consequence of El Niño precipitations led to an unusual increase in distribution and abundance of deer mice (; reservoir host of Sin Nombre virus). Could such drastic events occur in mesic habitats, where plant productivity in response to climate conditions is likely to be much less dramatic? In this work, we investigate to what extent deer mouse populations follow a precipitation-driven, bottom-up model in central and western Montana and discuss important conditions for such a model to be possible. We found positive correlations between deer mouse abundance and on-the-ground measured plant productivity with a several-month lag in three of six study sites. This effect was weaker when deer mouse populations were more abundant, indicating density-dependent effects. Dispersal resulting from territoriality may be important in attenuating local density increments in spite of high food availability. In addition, there is evidence that population abundance in the study area could respond to other abiotic factors. In particular, precipitation in the form of snow may reduce deer mice survival, thus compensating the benefits of improved plant productivity. Deer mouse populations in Montana study sites follow complex dynamics determined by multiple limiting factors, leading to a precipitation-driven bottom-up regulation. This prevents dramatic changes in rodent abundances after sudden increments of food availability, such as those observed in other regions.
小型哺乳动物的种群密度可受自下而上（食物可利用性）和自上而下（捕食）的力量调控。1993年，厄尔尼诺-南方涛动事件之后，美国西南部出现了一群感染汉坦病毒肺综合征的人。有人提出了一个上行营养级联假说来解释此次疫情爆发：厄尔尼诺降水导致植物生产力提高，进而致使鹿鼠（辛诺柏病毒的储存宿主）的分布范围和数量异常增加。在中生境中，植物生产力对气候条件的响应可能没那么显著，那么这种剧烈事件会在中生境中发生吗？在这项研究中，我们调查了蒙大拿州中部和西部的鹿鼠种群在多大程度上遵循降水驱动的自下而上模型，并讨论了该模型得以成立的重要条件。我们发现，在六个研究地点中的三个地点，鹿鼠数量与实地测量的植物生产力之间存在正相关，但有几个月的滞后。当鹿鼠种群数量较多时，这种影响就会减弱，这表明存在密度依赖效应。尽管食物供应充足，但领地行为导致的扩散可能对减弱当地密度增加很重要。此外，有证据表明，研究区域内的种群数量可能会对其他非生物因素作出反应。特别是，降雪形式的降水可能会降低鹿鼠的存活率，从而抵消植物生产力提高带来的好处。蒙大拿州研究地点的鹿鼠种群遵循由多种限制因素决定的复杂动态，导致了降水驱动的自下而上的调控。这就防止了在食物供应突然增加后，啮齿动物数量出现剧烈变化，比如在其他地区观察到的情况。
