Abstract
Point 1Management of crops, commercialized or protected species, plagues or life-cycle evolution are subjects requiring comparisons among different demographic strategies. The simpler methods fail in relating changes in vital rates with changes in population viability whereas more complex methods lack accuracy by neglecting interactions among vital rates.Point 2The difference between the fitness (evaluated by the population growth rate λ) of two alternative demographies is decomposed into the contributions of the differences between the pair-wised vital rates and their interactions. This is achieved through a full Taylor expansion (i.e. remainder = 0) of the demographic model. The significance of each term is determined by permutation tests under the null hypothesis that all demographies come from the same pool.Point 3An example is given with periodic demographic matrices of the microscopic haploid phase of two kelp cryptic species observed to partition their niche occupation along the Chilean coast. The method provided clear and synthetic results showing conditional differentiation of reproduction is an important driver for their differences in fitness along the latitudinal temperature gradient. But it also demonstrated that interactions among vital rates cannot be neglected as they compose a significant part of the differences between demographies.Point 4This method allows researchers to access the effects of multiple effective changes in a life-cycle from only two experiments. Evolutionists can determine with confidence the effective causes for changes in fitness whereas population managers can determine best strategies from simpler experimental designs.
Highlights
There are several reasons justifying comparison between demographies and their responses to the environment
We propose comparing each demography with the average demography and subjecting the results to a Principal Components Analysis (PCA)
The Taylor expansion analysis showed that sexual maturation and fertilization of female gametophytes are the key aspects of the kelp microstages differentiation between the two Lessonia sp cryptic species whereas spore settlement and germination is irrelevant. The niche partition they display along a latitudinal temperature gradient is set by their diverging fertility components of fitness and nothing else, at least within the microstages’ demography
Summary
There are several reasons justifying comparison between demographies and their responses to the environment. The geographical distribution of species and their abundance is often constrained by physiological limitations [1, 2, 3, 4, 5, 6] associated to environmental variables; temperature being considered a determinant factor with a significant impact on survival, reproduction and/or growth [7] This has often been observed in benthic marine macroalgae [8, 9, 10, 11, 12, 13]. It is relevant to compare the different demographic responses of populations of both competitors subject to the same environment In both cases it is necessary understanding how environmental factors affect the vital rates and the fitness of marine organisms [3, 14]. In order to do that, the multiple fitness components across the entire life cycle need be quantitatively estimated [15, 16]
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