On the variability of senescence trajectories

Background/Question/Methods

Senescence, a decline in survival probability or reproductive success with age, is a common feature of the life history of both animals and plants. Understanding senescence trajectories is important to conservation biology, biological demography and evolution. To understand senescence it is first necessary to describe it. Then, if we are to understand how aging patterns vary among taxonomic groups we must study the distribution of its metrics in a phylogenetic context. However, due to the existence of large amounts of demographic and phenotypic plasticity within species, the characterization of patterns for any particular species is not an easy task.

We use data from two demographic datasets, DATLife and COMPADRE II, and a number of individual-based datasets, to explore the nature of variability in the mortality and fertility trajectories of both animals and plants. We then assess how such variability can be an issue in interpreting evolutionary studies, and how these difficulties may be overcome. Finally we explore some of the opportunities that the existence of such variability presents.

Results/Conclusions

There is significant variability in the mortality and fertility trajectories of both animal and plant species, and the amount of variability varies greatly both among and within taxonomic groups. It is clear that our inferences on the processes occurring for particular species are dependent on the spatial and temporal replicative sampling regime used to collect the data. This has important implications if we use these trajectories to parameterise population models for management or conservation purposes, or in studies of the evolution of senescence.

We emphasize however, that demographic variability need not be a problem. Firstly, for comparative phylogenetic studies there are some simple ways of dealing with variation in the trait. We outline how this can be achieved. Secondly, it opens up the possibility of studying the nature of the variability - e.g. phenotypic plasticity- and how this varies among taxonomic groups. We present results of one such analysis.