Density and intercohort priority effects on larval Salamandra salamandra in temporary pools

Abstract

Priority effects, i.e., effects of an early cohort on the performance of a later cohort, are generally studied between, and not within, species. The paucity of intraspecific assessments does not reflect a lack of ecological importance, but the technical problem associated with differentiating between conspecific cohorts. Here, we examine priority and density-dependent effects on larval Salamandra salamandra infraimmaculata. Larvae deposited by their mother early in the season have increased risk of desiccation, as rains at the beginning of the season are less frequent and unpredictable. However, breeding later may incur a high cost through conspecific priority effects, including cannibalism and competition. In an outdoor artificial pool experiment, we established densities of 0, 1, 2, 4 or 6 newly born larvae per pool ( approximately 30 l), and 40 days later, added a second cohort of three newly born larvae to each pool. We differentiated between cohorts using natural individual-specific markings. For the early cohort, increasing density decreased survival and size at metamorphosis, and increased time to metamorphosis. For the late cohort, survival was 100% in pools without early-cohort larvae, but ranged between 13 and 33% in the presence of early-cohort larvae. Time to metamorphosis was significantly longer in the presence of low vs high densities of early-cohort larvae. Results suggest that early-cohort larvae are mainly subjected to exploitative competition and cannibalism mediated by food limitation, and that late-cohort larvae are subjected to cannibalism and interference due to size asymmetry between cohorts. The strong priority effects suggest that Salamandra females could increase their fitness by adjusting the number of larvae they deposit in specific pools to avoid cannibalism and intraspecific competition.

Phenological synchronization drives demographic rates of populations

“…The difference in arrival time between tadpoles in the high-synchrony treatment and the first cohort in the low-synchrony treatment was only three days, while the difference in mean development time between these treatments was nine days. These findings are consistent with prior work in other systems, which indicates that early-arriving cohorts can have strong negative effects on later-arriving ones (Hopper et al 1996, Sunahara and Mogi 2002, Eitam et al 2005. Our results also indicate that synchrony can alter the type of density-dependent competition and its effects on populations.…”

“…The degree of synchrony of offspring production, for example, determines the number of offspring that co-occur in time (increases with higher synchrony), as well as the amount of body size variation of offspring (decreases with higher synchrony). Density and relative body size are important factors determining the strength and type of intraspecific priority effects that occur among offspring (Hopper et al 1996, Sunahara and Mogi 2002, Eitam et al 2005, Geange and Stier 2009 1 E-mail: solifugae@gmail.com offspring production is high, offspring are similar in size when competition is initiated, which likely results in symmetric competition (i.e., scramble competition). In contrast, when offspring production occurs asynchronously, this creates variation in age/size among offspring, which could result in asymmetric competition (i.e., contest competition), favoring older/larger individuals.…”

Intraspecific priority effects and disease interact to alter population growth

“…This potential role of IPEs in interspecific competition remains unexplored, but would complement the large body of work examining priority effects between species (Chase 2003). IPEs may be more common in systems characterized by rapid population growth and clear spatial structure (though see Sunahara and Mogi [2002], Eitam et al [2005] for examples of IPEs among cohorts), including pioneer species in disturbed landscapes (e.g., Chapin et al 1994), metapopulations with high patch turnover (e.g., Hanski 2011), boundary zones of range expansion for invasive species (e.g., Sakai et al 2001), and pathogen interactions within and among hosts (de Roode et al 2005, Ben-Ami et al 2008, Hoverman et al 2013.…”

Natal-Host Environmental Effects on Juvenile Size, Transmission Success, and Operational Sex Ratio in the Entomopathogenic NematodeSteinernema carpocapsae

“…For example, larger offspring size can correlate with greater reproductive output, greater survival, or both (Stanton, 1984;Einum and Fleming, 2000a). Similarly, increased population density can lead to smaller adult size, causing decreased fecundity, survival, or both (Hirschberger, 1999;Eitam et al, 2005).…”