More Like this

1. Quantifying the conservation status and abundance trends of wildlife communities with detection–nondetection data

   https://doi.org/10.1111/cobi.13934  

   Farr, Matthew T. ; O'Brien, Timothy ; Yackulic, Charles B. ; Zipkin, Elise F. ( August 2022 , Conservation Biology)

   Effective conservation requires understanding species’ abundance patterns and demographic rates across space and time. Ideally, such knowledge should be available for whole communities because variation in species’ dynamics can elucidate factors leading to biodiversity losses. However, collecting data to simultaneously estimate abundance and demographic rates of communities of species is often prohibitively time intensive and expensive. We developed a multispecies dynamicN‐occupancy model to estimate unbiased, community‐wide relative abundance and demographic rates. In this model, detection–nondetection data (e.g., repeated presence–absence surveys) are used to estimate species‐ and community‐level parameters and the effects of environmental factors. To validate our model, we conducted a simulation study to determine how and when such an approach can be valuable and found that our multispecies model outperformed comparable single‐species models in estimating abundance and demographic rates in many cases. Using data from a network of camera traps across tropical equatorial Africa, we then used our model to evaluate the statuses and trends of a forest‐dwelling antelope community. We estimated relative abundance, rates of recruitment (i.e., reproduction and immigration), and apparent survival probabilities for each species’ local population. The antelope community was fairly stable (although 17% of populations [species–park combinations] declined over the study period). Variation in apparent survival was linked more closely to differences among national parks than to individual species’ life histories. The multispecies dynamicN‐occupancy model requires only detection–nondetection data to evaluate the population dynamics of multiple sympatric species and can thus be a valuable tool for examining the reasons behind recent biodiversity loss.

    

   more » « less
2. Comparing demography inferred from age vs. stage in a perennial plant

   https://doi.org/10.1002/ecy.3322  

   Alahuhta, Kirsi M. ; Crone, Elizabeth E. ; Lesica, Peter ( May 2021 , Ecology)

   Life history theories analyze and predict variation in vital rates, such as survival and reproduction, based on age. The age‐from‐stage method to derive age‐specific vital rates from stage data was developed because age‐specific data are rarely obtained for plants. Age‐specific vital rates derived by this method might underestimate effects of age on vital rates, because the models assume that vital rates do not vary within stage classes. Consequently, population models and life history summaries relying on these vital rates could be biased against detecting senescence. Here, we perform a comparative study of methods to estimate age‐specific vital rates using monitoring data with known age and stage. We derived age‐, stage‐, and age‐and‐stage‐specific vital rates with demographic data from a long‐lived perennial,Silene spaldingii. Then, we derived three age‐specific population matrix models (age, age‐from‐stage, and age‐and‐stage). For each model, we derived life history summaries commonly used in ecology: population growth rate, net reproductive value, relative reproductive values, stable age distribution, generation time, and sensitivity and elasticity of population growth rate. Many vital rates depended on both age and stage inS. spaldingii. However, this species does not senesce; in fact, the number of flowers increased with age. As expected, the age‐from‐stage method was not able to accurately recreate the age dependence in some life history summaries, such as relative reproductive value. The age‐from‐stage model suggested faster reproductive dynamics inS. spaldingiithan the models based on known age, i.e., plants started to reproduce earlier, and fertility remained constant thereafter, which may lead to biased predictions about evolutionary consequences of age‐dependent life history traits. However, population growth rate, generation time, and net reproductive rate did not differ significantly among the models. Our study demonstrated that some metrics are robust to imprecision in model structure, while others are more sensitive. In spite of these biases, this case study provides another example of the diversity of aging patterns in plants. Age can be essential information when studying senescence in plants, but demographic metrics that were not about age per se were similar across model structures.

    

   more » « less
3. Context‐dependent variability in the population prevalence and individual fitness effects of plant–fungal symbiosis

   https://doi.org/10.1111/1365-2745.13510  

   Donald, Marion L. ; Bohner, Teresa F. ; Kolis, Kory M. ; Shadow, R. Alan ; Rudgers, Jennifer A. ; Miller, Tom E. X. ; Wilson, ed., G. ( November 2020 , Journal of Ecology)

   Heritable symbionts are often observed at intermediate prevalence within host populations, despite expectations that positive fitness feedbacks should drive beneficial symbionts to fixation. Intermediate prevalence may reflect neutral dynamics of symbionts with weak fitness effects, transient dynamics of symbionts trending towards fixation (or elimination), or a stable intermediate outcome determined by the balance of fitness effects and failed symbiont transmission. Theory suggests that these outcomes should depend on symbiont‐conferred demographic effects and vertical transmission efficiency, which may both depend on environmental context.

   We established experimental populations of winter bent grassAgrostis hyemalisacross a range of prevalence of the heritable fungal endophyteEpichloë amarillans. Using irrigation, we elevated the precipitation for half of the populations, which we hypothesized would weaken the benefits of symbiosis. Across two annual transitions, we assayed 5,485 individuals to determine prevalence and censused 954 individuals for demographic (survival, flowering, reproduction and recruitment) and vertical transmission data. We used hierarchical Bayesian models to infer long‐run equilibria from short‐term changes in symbiont prevalence and estimated demographic vital rates to link individual‐level effects to population‐level outcomes.

   We found evidence for all three proposed mechanisms for intermediate symbiont prevalence, but the outcome differed qualitatively across years and precipitation treatments. In the first year, symbionts trended towards fixation under drought conditions but drifted neutrally under elevated precipitation. Fixation likely arose from symbiont‐conferred recruitment benefits outweighing reproductive costs under the drought conditions, while elevated precipitation tempered these effects. In the second transition year, we inferred stable intermediate prevalence across both precipitation treatments, which indicated a balance between symbiont conferred recruitment benefits that allowed low‐prevalence populations to increase and imperfect transmission that caused high‐prevalence populations to decrease.

   Synthesis. We find support for neutral, transient and stable mechanisms underlying symbiont prevalence, indicating that symbiont prevalence is often pushed and pulled in different directions by the composite outcome of symbiont effects on demographic rates and transmission efficiency, and the way in which these processes respond to environmental context.

    

   more » « less
4. Different population trajectories of two reef‐building corals with similar life‐history traits

   https://doi.org/10.1111/1365-2656.13463  

   Shlesinger, Tom ; van Woesik, Robert ( March 2021 , Journal of Animal Ecology)

   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
5. Estimating the net effect of functional traits on fitness across species and environments

   https://doi.org/10.1111/2041-210X.14079  

   Siefert, Andrew ; Laughlin, Daniel C. ( March 2023 , Methods in Ecology and Evolution)

   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