Hernandez Maria-Josefina, Barradas Ignacio
Laboratorio de Biología Teórica, Instituto de Zoología Tropical, Facultad de Ciencias, Universidad Central de Venezuela, Apartado Postal 47058, Caracas 1041-A, Venezuela.
J Math Biol. 2003 Jun;46(6):571-94. doi: 10.1007/s00285-002-0192-4.
The nature of the association between two species may vary depending on population abundances, age or size of individuals, or environmental conditions. Interactions may switch between beneficial and detrimental depending on the net balance of costs and benefits involved for each species. We study the repercussion of the ecological setting on the outcomes of conditional or variable interactions by means of a model that incorporates density-dependent interaction coefficients; that is, interaction alpha-functions. These characterize the responsiveness and sensitivity of the association to changes in partner's abundance, and can take positive and negative values. Variable outcomes - and transitions between them - are categorized as homeo- or allo-environmental, that is, occurring under the same ecological setting, or not, respectively. Bifurcation analyses show that these dynamics are moulded by ecological factors that are: intrinsic to the nature of the association (concerning the sensitivity of the interaction), and extrinsic to the association itself (the quality of the environment referred to each species alone). The influence of these factors may be conflicting; consequently, the dynamics involve catastrophic events. In a facultative variable association, stable coexistence is expected when environmental conditions are adverse; otherwise, the exclusion of one species is the likely outcome. Remarkable situations as the switching of victim-exploiter roles illustrate the theoretical perspective.
两个物种之间关联的性质可能会因种群丰度、个体的年龄或大小，或环境条件而有所不同。相互作用可能会根据每个物种所涉及的成本和收益的净平衡在有益和有害之间转换。我们通过一个纳入密度依赖相互作用系数的模型，即相互作用α函数，来研究生态环境对条件性或可变相互作用结果的影响。这些系数表征了这种关联对伙伴丰度变化的响应能力和敏感性，并且可以取正值和负值。可变结果以及它们之间的转变被分类为同环境或异环境的，也就是说，分别是在相同生态环境下发生的，或者不是。分岔分析表明，这些动态是由以下生态因素塑造的：关联性质固有的（关于相互作用的敏感性），以及关联本身外在的（单独针对每个物种而言的环境质量）。这些因素的影响可能相互冲突；因此，动态过程涉及灾难性事件。在一个兼性可变关联中，当环境条件不利时，预计会出现稳定共存；否则，一个物种被排除可能是结果。受害者 - 剥削者角色的转换等显著情况说明了这一理论观点。
