scholarly journals The evolution of growth rates on an expanding range edge

2009 ◽  
Vol 5 (6) ◽  
pp. 802-804 ◽  
Author(s):  
Ben L. Phillips
Keyword(s):  
Life History ◽  
Population Growth ◽  
Growth Rates ◽  
Life History Theory ◽  
Common Garden ◽  
Individual Growth ◽  
Dispersal Ability ◽  
Invasion Front ◽  
Range Edge ◽  
Theoretical Predictions

Individuals in the vanguard of a species invasion face altered selective conditions when compared with conspecifics behind the invasion front. Assortment by dispersal ability on the expanding front, for example, drives the evolution of increased dispersal, which, in turn, leads to accelerated rates of invasion. Here I propose an additional evolutionary mechanism to explain accelerating invasions: shifts in population growth rate ( r ). Because individuals in the vanguard face lower population density than those in established populations, they should (relative to individuals in established populations) experience greater r -selection. To test this possibility, I used the ongoing invasion of cane toads ( Bufo marinus ) across northern Australia. Life-history theory shows that the most efficient way to increase the rate of population growth is to reproduce earlier. Thus, I predict that toads on the invasion front will exhibit faster individual growth rates (and thus will reach breeding size earlier) than those from older populations. Using a common garden design, I show that this is indeed the case: both tadpoles and juvenile toads from frontal populations grow around 30 per cent faster than those from older, long established populations. These results support theoretical predictions that r increases during range advance and highlight the importance of understanding the evolution of life history during range advance.

scholarly journals Demographic compensation does not rescue populations at a trailing range edge

2017 ◽  
Author(s):  
Seema Nayan Sheth ◽  
Amy Lauren Angert
Keyword(s):  
Climate Change ◽  
Life History ◽  
Population Growth ◽  
Growth Rates ◽  
Time Lags ◽  
Vital Rates ◽  
Low Latitude ◽  
Species Ranges ◽  
Population Growth Rates ◽  
Range Edge

ABSTRACTAs climate change shifts species' climatic envelopes across the landscape, equilibrium between geographic ranges and niches is likely diminishing due to time lags in demography and dispersal. If a species' range and niche are out of equilibrium, then population performance should decrease from cool, “leading” range edges, where populations are expanding into recently ameliorated habitats, to warm, “trailing” range edges, where populations are contracting from newly unsuitable areas. Population contraction signals that compensatory changes in vital rates are insufficient to buffer population growth from deteriorating environments. Life history theory predicts tradeoffs between fast development, high reproduction, and short longevity at low latitudes and slow development, less frequent but multiple bouts of reproduction, and long lifespan at high latitudes. If demographic compensation is driven by life history evolution, compensatory negative correlations in vital rates may be associated with this fast-slow continuum. An outstanding question is whether range limits and range contractions reflect inadequate compensatory life history shifts along environmental gradients, causing population growth rates to fall below replacement levels at range edges. We surveyed demography of 32 populations of the scarlet monkeyflower (Erythranthe cardinalis) spanning 11° latitude in western North America and used integral projection models to infer population dynamics and assess demographic compensation. Population growth rates decreased from north to south, consistent with leading-trailing dynamics. Southern populations are declining due to reduced survival, growth, and recruitment, despite compensatory increases in reproduction and faster life history characteristics, suggesting that demographic compensation will not rescue populations at the trailing range edge.SIGNIFICANCE STATEMENTWhile climate change is causing poleward shifts in many species' geographic distributions, some species' ranges have remained stable, particularly at low-latitude limits. One explanation for why some species' ranges have not shifted is demographic compensation, whereby declines in some demographic processes are offset by increases in others, potentially buffering populations from extinction. However, we have limited understanding of whether demographic compensation can prevent collapse of populations facing climate change. We examined the demography of natural populations of a perennial herb spanning a broad latitudinal gradient. Despite increases in reproduction, low-latitude populations declined due to diminished survival, growth, and recruitment. Thus, demographic compensation may not be sufficient to rescue low-latitude, warm-edge populations from extinction.

Life history and environmental influences on population dynamics in sockeye salmon

2014 ◽  
Vol 71 (8) ◽  
pp. 1198-1208 ◽  
Author(s):  
Douglas C. Braun ◽  
John D. Reynolds
Keyword(s):  
Population Dynamics ◽  
Life History ◽  
Population Growth ◽  
Growth Rates ◽  
Environmental Conditions ◽  
Sockeye Salmon ◽  
Life History Traits ◽  
Relative Importance ◽  
Population Growth Rates ◽  
Habitat Variables

Understanding linkages among life history traits, the environment, and population dynamics is a central goal in ecology. We compared 15 populations of sockeye salmon (Oncorhynchus nerka) to test general hypotheses for the relative importance of life history traits and environmental conditions in explaining variation in population dynamics. We used life history traits and habitat variables as covariates in mixed-effect Ricker models to evaluate the support for correlates of maximum population growth rates, density dependence, and variability in dynamics among populations. We found dramatic differences in the dynamics of populations that spawn in a small geographical area. These differences among populations were related to variation in habitats but not life history traits. Populations that spawned in deep water had higher and less variable population growth rates, and populations inhabiting streams with larger gravels experienced stronger negative density dependence. These results demonstrate, in these populations, the relative importance of environmental conditions and life histories in explaining population dynamics, which is rarely possible for multiple populations of the same species. Furthermore, they suggest that local habitat variables are important for the assessment of population status, especially when multiple populations with different dynamics are managed as aggregates.

The effects of social status on life-history variation in juvenile salmon

1990 ◽  
Vol 68 (12) ◽  
pp. 2630-2636 ◽  
Author(s):  
Neil B. Metcalfe ◽  
Felicity A. Huntingford ◽  
John E. Thorpe ◽  
Colin E. Adams
Keyword(s):  
Life History ◽  
Social Status ◽  
Growth Rates ◽  
Individual Growth ◽  
Laboratory Population ◽  
High Status ◽  
Life History Variation ◽  
High Ranking ◽  
Clear Cut ◽  
Modal Group

Under good growing conditions, juvenile Atlantic salmon metamorphose into the migratory smolt stage at 1+ or 2+ years of age. The life-history decision on whether or not to migrate at 1+ years is made in July–August of the previous year. After this time, populations develop a bimodal size distribution, the larger fish (upper modal group) being the 1+ smolts and the lower modal group being fish that will smolt at 2+. Fish of high social status are more likely to become 1+ smolts. We examined the causal nature of this relationship by manipulating status within a laboratory population of sibling fish. The absolute status of individual fish was estimated within 2 weeks of first feeding. Relative status was then manipulated by dividing the population into two, half containing the fish with the highest absolute status (high ranking) and the remaining half of fish of lowest absolute status (low ranking). The status of individually marked fish was then determined within each of the two groups. Individual growth rates were monitored until smolting strategies were apparent. There was a complete overlap in the sizes of subsequent upper and lower modal group parr in early June, but from late June onwards fish in the upper modal group grew faster. The high- and low-ranking groups did not differ either in mean growth rates or in the proportions of fish adopting the alternative smolting strategies. However, they differed in the factors that influenced an individual's developmental strategy: within the high-ranking group, relative social status in June was a significant predictor of whether a fish would smolt aged 1+, whereas length at that time was not. In contrast, no relationship between status and smolting strategy was found in the low-ranking group, where differences in status were less clear-cut and had less influence on growth. Instead, age of smolting could be predicted from early growth rate. These results demonstrate that the influence of status on smolting depends on the extent to which fish of high status suppress the growth of those lower in the hierarchy.

scholarly journals Diet and divergence of introduced smallmouth bass (Micropterus dolomieu) populations

2005 ◽  
Vol 62 (8) ◽  
pp. 1720-1732 ◽  
Author(s):  
Erin S Dunlop ◽  
Judi A Orendorff ◽  
Brian J Shuter ◽  
F Helen Rodd ◽  
Mark S Ridgway
Keyword(s):  
Life History ◽  
Food Availability ◽  
Life History Theory ◽  
Reproductive Investment ◽  
Adult Mortality ◽  
Smallmouth Bass ◽  
Individual Growth ◽  
Common Source ◽  
Large Prey ◽  
Micropterus Dolomieu

We examine the degree and causes of divergence in growth and reproduction in two populations of smallmouth bass (Micropterus dolomieu) introduced a century ago. Despite a common source, the Provoking Lake population now has a higher population density and slower growing individuals than the Opeongo Lake population. Using this system, we test the predictions of life history theory that delayed maturation and reduced reproductive investment are expected in high density populations with slow individual growth rates. Observations on both populations run directly counter to the aforementioned expectations. Instead, Provoking males have smaller sizes and younger ages at nesting and higher gonad masses than Opeongo males; Provoking females have smaller sizes at maturity, larger egg sizes, and higher ovarian dry masses than Opeongo females. Temperature, food availability, diet ontogeny, young-of-the-year mortality, and adult mortality were examined as plausible contributors to the divergence. Results suggest that low food availability, likely caused or mediated by intraspecific competition for prey, and lack of large prey in the diet are contributing to the slow growth, increased reproductive investment, and higher mortality following reproduction in Provoking. This study provides insight into the processes that produce rapid divergence of life history in a species exhibiting parental care.

scholarly journals The stagnation paradox: the ever-improving but (more or less) stationary population fitness

2021 ◽  
Vol 288 (1963) ◽  
Author(s):  
Hanna Kokko
Keyword(s):  
Population Growth ◽  
Growth Rates ◽  
Life History Theory ◽  
Genetic Studies ◽  
Population Growth Rates ◽  
Microevolutionary Change ◽  
Mean Fitness ◽  
Zero Sum ◽  
Fisher’S Fundamental Theorem ◽  
Population Fitness

Fisher's fundamental theorem states that natural selection improves mean fitness. Fitness, in turn, is often equated with population growth. This leads to an absurd prediction that life evolves to ever-faster growth rates, yet no one seriously claims generally slower population growth rates in the Triassic compared with the present day. I review here, using non-technical language, how fitness can improve yet stay constant (stagnation paradox), and why an unambiguous measure of population fitness does not exist. Subfields use different terminology for aspects of the paradox, referring to stasis, cryptic evolution or the difficulty of choosing an appropriate fitness measure; known resolutions likewise use diverse terms from environmental feedback to density dependence and ‘evolutionary environmental deterioration’. The paradox vanishes when these concepts are understood, and adaptation can lead to declining reproductive output of a population when individuals can improve their fitness by exploiting conspecifics. This is particularly readily observable when males participate in a zero-sum game over paternity and population output depends more strongly on female than male fitness. Even so, the jury is still out regarding the effect of sexual conflict on population fitness. Finally, life-history theory and genetic studies of microevolutionary change could pay more attention to each other.

Life in the Slow Lane: Ecology and Conservation of Long-Lived Marine Animals

1999 ◽  
Keyword(s):  
Life History ◽  
Population Growth ◽  
Growth Rates ◽  
Anthropogenic Impacts ◽  
Survival Rates ◽  
Conservation Strategies ◽  
Adult Survival ◽  
Population Growth Rates ◽  
Important Prey ◽  
The Status

<em>Abstract.</em> —Seabirds become mature at a late age, experience low annual fecundity, often refrain from breeding, and enjoy annual adult survival rates as high as 98%. This suite of life history characteristics limits the capacity for seabird populations to recover quickly from major perturbations, and presents important conservation challenges. Concern over anthropogenic impacts on seabird populations has led to the initiation of long-term field programs to monitor seabird reproductive performance and population dynamics. In addition, seabirds have been recognized as potentially useful and economical indicators of the state of the marine environment and, in particular, the status of commercially important prey stocks. This paper reviews demographic and life history attributes of seabird populations and uses this information to explore the consequences of longevity from the respective standpoints of conservation and monitoring goals. Analysis of a simplified life cycle model reveals that maximum potential population growth rates (λ) under ideal circumstances fall within the range of 1.03–1.12 for most species, though growth rates realized in nature will always be lower. Elasticity analysis confirms that seabird population growth rates are extremely sensitive to small variations in adult survival rates, and dictates that survival monitoring should be considered an essential component of conservation strategies. As in other organisms with long life spans, ecological and physiological costs of reproduction are expected to figure prominently in seabird reproductive decisions. Consequently, understanding how seabirds allocate reproductive effort in response to varying environmental conditions is an important prerequisite for correctly interpreting field data from monitoring studies.

Annual life-history variation in the striped plateau lizard, Sceloporus virgatus

1996 ◽  
Vol 74 (11) ◽  
pp. 2025-2030 ◽  
Author(s):  
Geoffrey R. Smith
Keyword(s):  
Life History ◽  
Body Mass ◽  
Growth Rates ◽  
Individual Growth ◽  
First Year ◽  
Life History Variation ◽  
Demographic Traits ◽  
Sceloporus Virgatus ◽  
One Year ◽  
Annual Life History

I studied temporal variation in life-history and demographic traits of a population of striped plateau lizards, Sceloporus virgatus, over 3 years in the Chiricahua Mountains of southeastern Arizona. The 3 years of the study varied in precipitation and arthropod (prey) abundance, but the 2 years for which data were available did not differ in the amount of time potentially available for lizard activity. Individual growth, gain in body mass, and adult survivorship varied among years, the year of lowest precipitation levels (1994) having the slowest growth rates (0.099 mm/d) and gain in body mass (0.008 g/d) and the lowest adult survivorship (0.28), and the year of highest precipitation levels (1992) having the fastest growth rates (0.117 mm/d) and gain in body mass (0.029 g/d) and the highest adult survivorship (0.40). The proportion of first-year females that reproduced, juvenile survivorship, sex ratio, and age structure of the population did not differ among years. Individuals that grew faster (or slower) than expected from their body size in one year grew faster (or slower) than expected the next year. Survivors (both male and female) did not grow faster than nonsurvivors. Precipitation appears to be the strongest proximate factor influencing annual life-history traits in this population, probably because of its influence on arthropod abundance.

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