skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Friday, July 12 until 2:00 AM ET on Saturday, July 13 due to maintenance. We apologize for the inconvenience.

Title: Different population trajectories of two reef‐building corals with similar life‐history traits

Increases in the frequency and intensity of acute and chronic disturbances are causing declines of coral reefs world‐wide. Although quantifying the responses of corals to acute disturbances is well documented, detecting subtle responses of coral populations to chronic disturbances is less common, but can also result in altered population and community structures.

We investigated the population dynamics of two key reef‐building Merulinid coral species,Dipsastraea favusandPlatygyra lamellina, with similar life‐history traits, in the Gulf of Eilat and Aqaba, Red Sea from 2015 to 2018, to assess potential differences in their population trajectories.

Demographic processes, which included rates of survival, growth, reproduction and recruitment were used to parametrize integral projection models and estimate population growth rates and the likely population trajectories of both coral species.

The survival and reproduction rates of bothD. favusandP. lamellinawere positively related to coral colony size, and elasticity analyses showed that large colonies most influenced population dynamics. Although both species have similar life‐history traits and growth morphologies and are generally regarded as ‘stress‐tolerant’, the populations showed contrasting trajectories—D. favusappears to be increasing whereasP. lamellinaappears to be decreasing.

As many corals have long‐life expectancies, the process of local and regional decline might be subtle and slow. Ecological assessments based on total living coral coverage, morphological groups or functional traits might overlook subtle, species‐specific trends. However, demographic approaches capable of detecting subtle species‐specific population changes can augment ecological studies and provide valuable early warning signs of decline before major coral loss becomes evident.

more » « less
Award ID(s):
Author(s) / Creator(s):
Publisher / Repository:
Date Published:
Journal Name:
Journal of Animal Ecology
Page Range / eLocation ID:
p. 1379-1389
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    It has been proposed that in slow‐growing vertebrate populations survival generally has a greater influence on population growth than reproduction. Despite many studies cautioning against such generalizations for conservation, wildlife management for slow‐growing populations still often focuses on perturbing survival without careful evaluation as to whether those changes are likely or feasible. Here, we evaluate the relative importance of reproduction and survival for the conservation of two bottlenose dolphin (Tursiopscfaduncus) populations: a large, apparently stable population and a smaller one that is forecast to decline. We also assessed the feasibility and effectiveness of wildlife management objectives aimed at boosting either reproduction or survival. Consistent with other analytically based elasticity studies, survival had the greatest effect on population trajectories when altering vital rates by equal proportions. However, the findings of our alternative analytical approaches are in stark contrast to commonly used proportional sensitivity analyses and suggest that reproduction is considerably more important. We show that

    in the stable population reproductive output is higher, and adult survival is lower;

    the difference in viability between the two populations is due to the difference in reproduction;

    reproductive rates are variable, whereas survival rates are relatively constant over time;

    perturbations on the basis of observed, temporal variation indicate that population dynamics are much more influenced by reproduction than by adult survival;

    for the apparently declining population, raising reproductive rates would be an effective and feasible tool to reverse the forecast population decline; increasing survival would be ineffective.

    Our findings highlight the importance of reproduction – even in slow‐growing populations – and the need to assess the effect of natural variation in vital rates on population viability. We echo others in cautioning against generalizations based on life‐history traits and recommend that population modeling for conservation should also take into account the magnitude of vital rate changes that could be attained under alternative management scenarios.

    more » « less
  2. Abstract

    Functional traits affect the demographic performance of individuals in their environment, leading to fitness differences that scale up to drive population dynamics and community assembly. Understanding the links between traits and fitness is, therefore, critical for predicting how populations and communities respond to environmental change. However, the net effects of traits on species fitness are largely unknown because we have lacked a framework for estimating fitness across multiple species and environments.

    We present a modelling framework that integrates trait effects on demographic performance over the life cycles of individuals to estimate the net effect of traits on species fitness. This approach involves (1) modelling trait effects on individual demographic rates (growth, survival and recruitment) as multidimensional performance surfaces that vary with individual size and environment and (2) integrating these effects into a population model to project population growth rates (i.e., fitness) as a function of traits and environment. We illustrate our approach by estimating performance surfaces and fitness landscapes for trees across a temperature gradient in the eastern United States.

    Functional traits (wood density, specific leaf area and maximum height) interacted with individual size and temperature to influence tree growth, survival and recruitment rates, generating demographic trade‐offs and shaping the contours of fitness landscapes. Tall tree species had high survival, growth and fitness across the temperature gradient. Wood density and specific leaf area had interactive effects on demographic performance, resulting in fitness landscapes with multiple peaks.

    With this approach it is now possible to empirically estimate the net effect of traits on fitness, leading to an improved understanding of the selective forces that drive community assembly and permitting generalizable predictions of population and community dynamics in changing environments.

    more » « less
  3. Abstract

    Crayfish play a crucial ecological role and are often considered a keystone species within freshwater ecosystems; however, North American crayfish species face disturbance and ecological threats including invasive species and intensified drought.

    Demographic models can allow examination of population dynamics of a targeted species under a wide variety of disturbance scenarios. In this study, crayfish population dynamics were modelled and their responses to simulated biological invasions and drought were assessed.

    As life history data on crayfish are relatively rare, models were used to explore the population viability of four generalized species with distinct life history strategies under 11 disturbance scenarios. RAMAS‐Metapop was used to construct stage‐based demographic metapopulation models parameterized using vital rates from established literature sources.

    Models indicated that populations respond differentially to disturbance based on life history. However, bothr‐ andK‐selected species appear to be highly susceptible to decline when faced with the additive effects of reduced carrying capacity resulting from invasion and reduced survival rates caused by drought.

    Constructing models that explore a broad array of life histories and disturbance regimes can provide managers with tools to develop generalized, widely applicable conservation strategies in data‐depauperate systems.

    more » « less
  4. Abstract

    Increasing harvest and overexploitation of wild plants for non‐timber forest products can significantly affect population dynamics of harvested populations. While the most common approach to assess the effect of harvest and perturbation of vital rates is focused on the long‐term population growth rate, most management strategies are planned and implemented over the short‐term.

    We developed an integral projection model to investigate the effects of harvest on the demography and the short‐ and long‐term population dynamics ofBanisteriopsis caapiin the Peruvian Amazon rainforest.

    Harvest had no significant effect on the size‐dependent growth of lianas, but survival rates increased with size. Harvest had a significant negative effect on size‐dependent survival where larger lianas experienced greater mortality rates under high harvest pressure than smaller lianas. In the populations under high harvest pressure, survival of smaller lianas was greater than that of populations with low harvest pressure. Harvest had no significant effect on clonal or sexual reproduction, but fertility was size‐dependent.

    The long‐term population growth rates ofB. caapipopulations under high harvest pressure were projected to decline at a rate of 1.3% whereas populations with low harvest pressure are expected to increase at 3.2%. However, before reaching equilibrium, over the short‐term, allB. caapipopulations were in decline by 26% (high harvested population) and (low harvested population) 20.4% per year.

    Elasticity patterns were dominated by survival of larger lianas irrespective of harvest treatments. Life table response experiment analyses indicated that high harvest caused the 6% reduction in population growth rates by significantly reducing the survival of large lianas and increasing the survival‐growth of smaller lianas including vegetative reproductive individuals.

    Synthesis and applications. This study emphasizes how important it is for management strategies forB. caapilianas experiencing anthropogenic harvest to prioritize the survival of larger size lianas and vegetative reproducing individuals, particularly in increased harvested systems often prone to multiple stressors. From an applied conservation perspective, our findings illustrate the importance of both prospective and retrospective perturbation analyses in population growth rates in understanding the population dynamics of lianas in general in response to human‐induced disturbance.

    more » « less
  5. Abstract

    Extreme climatic events may influence individual‐level variability in phenotypes, survival and reproduction, and thereby drive the pace of evolution. Climate models predict increases in the frequency of intense hurricanes, but no study has measured their impact on individual life courses within animal populations.

    We used 45 years of demographic data of rhesus macaques to quantify the influence of major hurricanes on reproductive life courses using multiple metrics of dynamic heterogeneity accounting for life course variability and life‐history trait variances.

    To reduce intraspecific competition, individuals may explore new reproductive stages during years of major hurricanes, resulting in higher temporal variation in reproductive trajectories. Alternatively, individuals may opt for a single optimal life‐history strategy due to trade‐offs between survival and reproduction.

    Our results show that heterogeneity in reproductive life courses increased by 4% during years of major hurricanes, despite a 2% reduction in the asymptotic growth rate due to an average decrease in mean fertility and survival by that is, shortened life courses and reduced reproductive output. In agreement with this, the population is expected to achieve stable population dynamics faster after being perturbed by a hurricane (; 95% CI: 1.488, 1.538), relative to ordinary years .

    Our work suggests that natural disasters force individuals into new demographic roles to potentially reduce competition during unfavourable environments where mean reproduction and survival are compromised. Variance in lifetime reproductive success and longevity are differently affected by hurricanes, and such variability is mostly driven by survival.

    more » « less