Estimating mortality: Clarifying assumptions and sources of uncertainty in vertical methods

Gentleman, Wendy C.; Pepin, Pierre; Doucette, Sarah

doi:10.1016/j.jmarsys.2012.05.006

Cited by 18 publications

(30 citation statements)

References 71 publications

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“…For copepods, daily survival rates range from close to 0 and up to 20% of the individuals dying (e.g. Aksnes and Ohman 1996;Gentleman et al 2012), representing life expectancies from around 2 weeks to several years. Consequently, we tested a range of mortality rates m a ∈ ⟨0.005, 0.035⟩ for the feeding habitat, broad enough to cover observed variability of adult and juvenile life expectancies in a range of arthropods (e.g.…”

Section: Breeding Strategies and Mortality Ratementioning

confidence: 99%

Trade-offs between storage and survival affect diapause timing in capital breeders

Varpe

Ejsmond

2018

Evol Ecol

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Many organisms spend the unfavourable part of the year, such as the winter season, in diapause or dormancy and reproduce in spring shortly after emergence. Reserves are acquired prior to diapause to cover metabolic costs and in some species also reproduction (capital breeding) directly after diapause. Storage is then a component of future reproduction, and capital breeders consequently pay a pre-breeding cost of reproduction as they risk dying while obtaining and carrying the reserves. How large should the reserves be, and to what extent should optimal storage, and thereby timing of diapause, depend on predation risk and reproductive strategy? We present a general and simplistic life history model of an arthropod (e.g. crustaceans or insects) that is exposed to background mortality risk when it accumulates reserves before diapause. The model optimizes diapause timing and resultant reserves for income, mixed and capital breeders, and predicts how mortality risk affects the degree of capital breeding. For income breeders, timing of diapause is insensitive to the risk while obtaining reserves as they, regardless of risk, acquire the minimum amount needed to survive the winter. For capital breeders, the higher the risk the earlier the diapause and less is consequently stored. Mixed breeders diapause late and store as much as pure capital breeders when exposed to low risk, but behave as income breeders and diapause early when mortality is high. Our model shows that the degree of capital breeding impacts phenology of diapause in a risk-dependent manner. This prediction should impact how diapause timing is thought of across a wide range of taxa, including the much studied marine copepods. Timing of diapause, including triggers and cues, can only be understood when the diversity of reproductive strategies and the adaptive value of storage is taken into account.

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Section: Breeding Strategies and Mortality Ratementioning

confidence: 99%

Trade-offs between storage and survival affect diapause timing in capital breeders

Varpe

Ejsmond

2018

Evol Ecol

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“…As a result there has been relatively little attempt to quantify the impact of mortality on populations. However, some recent research has attempted to provide a clearer direction for the rigorous quantification of mortality in Calanus (Ohman, 2012;Gentleman et al, 2012).…”

Section: Mortalitymentioning

confidence: 99%

On the surprising lack of differences between two congeneric calanoid copepod species, Calanus finmarchicus and C. helgolandicus

Wilson

Speirs

Heath

2015

Progress in Oceanography

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The important calanoid copepod species Calanus finmarchicus and C. helgolandicus have distinct geographic ranges which are changing under the influence of climate change. Understanding the mechanisms underlying their distributions is becoming increasingly important as a result of the possible ecological impacts of these range shifts. Here we review inter-species differences in key life cycle traits that influence each species’ geographic distribution, in particular development and growth, fecundity, feeding behaviour, vertical migration and overwintering behaviour. The distinct temperature niche of each species leads to an a priori assumption that the response of life cycle traits to temperature is a key determinant of their contrasting geographic distributions. A new development model was created to reconcile published experimental development times for each species. Model output indicates that at temperatures below approximately 12-13 ˚C, C. finmarchicus is the faster developing species, but above these temperatures C. helgolandicus develops more quickly. Conventionally Calanus development time is assumed to decrease monotonically with temperature; however our model indicates that the response of development time to temperature is instead U-shaped. Differences in life cycle aspects such as seasonality and vertical structuring are interpreted in light of this development model. Body size and lipid accumulation abilities could be significant influences on each species’ geographic distribution; however evidence is consistent with inter-species differences not existing for these traits. Published evidence shows that inter-species differences in egg production may exist, but do not follow a clear pattern. Diapause is an important and well studied life cycle adaptation of C. finmarchicus, but has received little attention in C. helgolandicus. We synthesised knowledge of diapause and suggest the hypothesis that C. helgolandicus is restricted to continental shelf regions as a result of an inability to diapause for significant periods. This synthesised view of each species’ respective life cycle traits is that response of growth and development to temperature is the only known difference between each species, which indicates a promising direction for the extension of population models of C. finmarchicus to C. helgolandicus

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“…This problem is equivalent to that for mortality, which is often calculated using the Ratio method by which mortality is determined between successive pairs of stages (Gentleman et al, 2012). Alternatively, mortality can be assumed constant across several stages (Kimmerer, 2015), as we have done here for growth.…”

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confidence: 99%

Effects of freshwater flow and phytoplankton biomass on growth, reproduction, and spatial subsidies of the estuarine copepod Pseudodiaptomus forbesi

et al. 2017

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We examined how freshwater flow and phytoplankton biomass affected abundance and population dynamics of the introduced subtropical copepod Pseudodiaptomus forbesi in brackish and freshwater regions of the San Francisco Estuary, California, USA. This copepod is key prey for the endangered and food-limited delta smelt, Hypomesus transpacificus, in low-salinity water during summerautumn. Long-term monitoring data showed that P. forbesi was most abundant in fresh water, where summer-autumn abundance was invariant with freshwater flow. Abundance was positively related to freshwater flow in low-salinity water. Reproductive rates in both regions during 2010-2012 were low and unresponsive to chlorophyll or freshwater flow. Development indices, calculated as ratios of laboratory-derived to field-derived stage durations, were lowest for nauplii and highest for late copepodites, but averaged below 0.5 for all stages combined. Development indices were weakly related to chlorophyll for late copepodites only, unrelated to freshwater flow, and slightly higher in low-salinity than fresh water. Thus, the principal mechanism by which flow affects the P. forbesi population is apparently transport of copepods from fresh water to low-salinity water, where copepods are available to delta smelt. This work demonstrates how freshwater flow affects estuarine foodwebs through spatial subsidies of food supply.

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Estimating mortality: Clarifying assumptions and sources of uncertainty in vertical methods

Cited by 18 publications

References 71 publications

Trade-offs between storage and survival affect diapause timing in capital breeders

Trade-offs between storage and survival affect diapause timing in capital breeders

On the surprising lack of differences between two congeneric calanoid copepod species, Calanus finmarchicus and C. helgolandicus

Effects of freshwater flow and phytoplankton biomass on growth, reproduction, and spatial subsidies of the estuarine copepod Pseudodiaptomus forbesi

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