Match or mismatch: the influence of phenology on size‐dependent life history and divergence in population structure

Abstract

Summary1. In gape-limited predators, body size asymmetries determine the outcome of predator-prey interactions. Due to ontogenetic changes in body size, the intensity of intra-and interspecific interactions may change rapidly between the match situation of a predator-prey system and the mismatch situation in which competition, including competition with the prey, dominates. 2. Based on a physiologically structured population model using the European perch (Perca fluviatilis), analysis was performed on how prey density (bream, Abramis brama), initial size differences in the young-of-the-year (YOY) age cohort of the predator, and phenology (time-gap in hatching of predator and prey) influence the size structure of the predator cohort. 3. In relation to the seasonality of reproduction, the match situation of the predator-prey system occurred when perch hatched earlier than bream and when no gape-size limitations existed, leading to decreased size divergence in the predator age cohort. Decreased size divergence was also found when bream hatched much earlier than perch, preventing perch predation on bream occurring, which, in turn, increased the competitive interaction of the perch with bream for the common prey, zooplankton; i.e. the mismatch situation in which also the mean size of the age cohort of the predator decreased. 4. In between the total match and the mismatch, however, only the largest individuals of the perch age cohort were able to prey on the bream, while smaller conspecifics got trapped in competition with each other and with bream for zooplankton, leading to enlarged differences in growth that increased size divergence. 5. The modelling results were combined with 7 years of field data in a lake, where large differences in the length-frequency distribution of YOY perch were observed after their first summer. These field data corroborate that phenology and prey density per predator are important mechanisms in determining size differences within the YOY age cohort of the predator.6. The results demonstrate that the switch between competitive interactions and a predator-prey relationship depended on phenology. This resulted in pronounced size differences in the YOY age cohort, which had far-reaching consequences for the entire predator population.

Feeding and niche differentiation in three invasive gobies in the Lower Rhine, Germany

“…With increasing size and, thus, decreasing gape size limitations, the potential to use more diverse prey items regularly increases, and consequently, competition on food resources may be reduced (Beeck et al, 2002;De Roos et al, 2003;Borcherding et al, 2010). Similar as for the juveniles, the adults of P. kessleri had a significantly higher ISF than N. melanostomus while co-occurring in the riprap structures (Fig.…”

The role of winter phenology in shaping the ecology of freshwater fish and their sensitivities to climate change

“…In fall spawners, this can stem from factors such as exposure to higher, harmful temperatures in fall (Casselman 2002) and premature hatching in spring that leads to a mismatch between initiation of larval feeding and the start of the spring production pulse (Pörtner and Peck 2010). De-synchronization of matched feeding phenologies (and vice versa) among younger and older fish can also change inter-specific interactions from predation to competition (and vice versa) with significant consequences for both growth and survival (Borcherding et al 2010). In spring river spawners, de-sychronization of the typical flood cycle from the fixed photoperiod cycle may have similar effects on species that use the timing of the first spring flood as the proximate cue to initiate spawning migrations.…”

A new mechanistic approach for the further development of a population with established size bimodality

“…Many studies on the development of bimodality either identified an initial size difference [12] or a single discrete accelerated growth period of one part of the population [1,13] as the origin of within-cohort size variation. However, in a population with a bimodal size distribution, there are often also some individuals with intermediate size.…”

“…Such a static view may, however, neglect dynamic processes that allow some individuals within the cohort to shift from the smaller to the larger fraction, beyond initial size differences or one-time growth accelerations. One consequence of a broad size-distribution (like bimodality) within an age-cohort can be mainly attributed to differential resource use and the consequential reduction of intra-cohort competition [13,14,15]. One can hypothesize the existence of medium-sized individuals that consume alternative food resources that are not used by the bulk of small or large individuals (e.g., feeding on macroinvertebrates if the majority of the conspecifics prey zooplankton).…”