Microhabitat heterogeneity and a non‐native avian frugivore drive the population dynamics of an island endemic shrub, Cyrtandra dentata

Abstract

Summary Understanding the role of environmental change in the decline of endangered species is critical for designing scale‐appropriate restoration plans. For locally endemic rare plants on the brink of extinction, frugivory can drastically reduce local recruitment by dispersing seeds away from geographically isolated populations. Dispersal of seeds away from isolated populations can ultimately lead to population decline. For localized endemic plants, fine‐scale changes in microhabitat can further limit population persistence. Evaluating the individual and combined impact of frugivores and microhabitat heterogeneity on the short‐term (i.e. transient) and long‐term (i.e. asymptotic) dynamics of plants will provide insight into the drivers of species rarity. In this study, we used 4 years of demographic data to develop matrix projection models for a long‐lived shrub, Cyrtandra dentata (H. St. John & Storey) (Gesneriaceae), which is endemic to the island of O'ahu in Hawai'i. Furthermore, we evaluated the individual and combined influence of a non‐native frugivorous bird, Leiothrix lutea, and microhabitat heterogeneity on the short‐term and long‐term C. dentata population dynamics. Frugivory by L. lutea decreased the short‐term and long‐term population growth rates. However, under the current level of frugivory at the field site the C. dentata population was projected to persist over time. Conversely, the removal of optimum microhabitat for seedling establishment (i.e. rocky gulch walls and boulders in the gulch bottom) reduced the short‐term and long‐term population growth rates from growing to declining. Survival of mature C. dentata plants had the greatest influence on long‐term population dynamics, followed by the growth of seedlings and immature plants. The importance of mature plant survival was even greater when we simulated the combined effect of frugivory and the loss of optimal microhabitat, relative to population dynamics based on field conditions. In the short‐term (10 years), however, earlier life stages had the greatest influence on population growth rate. Synthesis and applications. This study emphasizes how important it is to decouple rare plant management strategies in the short vs. long‐term in order to prioritize restoration actions, particularly when faced with multiple stressors not all of which can be feasibly managed. From an applied conservation perspective, our findings also illustrate that the life stage that, if improved by management, would have the greatest influence on population dynamics is dependent on the timeframe of interest and initial conditions of the population.

Increased clonal growth in heavily harvested ecosystems failed to rescue ayahuasca lianas from decline in the Peruvian Amazon rainforest

“…Such differences could be explained by low seedling recruitment in the liana populations and subsequent lack of change in the number of young individuals over time. It has been cautioned that long‐term elasticity analysis may not always adequately describe the relative importance of vital rate life stage contributions to the short‐term population growth rate (Bialic‐Murphy et al, 2017; Haridas & Tuljapurkar, 2007). Thus, we suggest future research investigating both the short‐ and long‐term elasticity patterns of B. caapi is critical to understanding the population dynamics of lianas and for the development of sound management plans for this culturally and economically important NTFP plant species.…”

“…These approaches which are solely based on long‐term projections, may underestimate the short‐term effects of harvest (Gaoue, 2016). Elasticity analyses of short‐term population dynamics are likely critical for the development of robust management plans (Bialic‐Murphy et al, 2017; Gaoue, 2016), especially, for economically important plant species that are harvested under various harvest regimes. Furthermore, understanding the relative contribution of vital rates to differences in population growth rates prospectively and retrospectively will prove informative (Caswell, 2000).…”

Assessing the roles of seed bank, seed dispersal and historical disturbances for metapopulation persistence of a pyrogenic herb

“…In this study, we were interested in the role of dispersal among patches and landscape structure on population variation and assumed homogeneous environmental conditions with the patches. We recognize that microhabitat heterogeneity and the consequences of short distance dispersal on demography are important (Bialic‐Murphy, Gaoue, & Kawelo, ; Godínez‐Alvarez & Jordano, ; Loayza & Knight, ), but the analysis of these factors on our focal species is beyond the scope of this work.…”

The Disconnect Between Short- and Long-Term Population Projections for Plant Reintroductions

“…Previous studies have demonstrated that perturbations of earlier life stages are often more important in the transient phase than in the asymptotic phase (Fox and Gurevitch, 2000;McMahon and Metcalf, 2008;Haridas and Gerber, 2010;Miller and Tenhumberg, 2010;Bialic-Murphy et al, 2017). Furthermore, anthropogenic stressors can have a greater negative effect on the short-term population growth rate under more optimal abiotic conditions than less optimal abiotic conditions (Gaoue, 2016).…”

“…The use of short-and long-term population projections to characterize how skewed stage structures influence plant population dynamics over time has become increasingly important for understanding the effects of environmental change on fundamental patterns in ecology. For example, short-and long-term projections have been used to characterize plant population responses to herbivory pressure (Maron et al, 2010), harvesting (Gaoue, 2016), biological invasion (McMahon and Metcalf, 2008;Ezard et al, 2010), severe catastrophic events (Crain et al, 2019), and habitat disturbance (Ezard et al, 2010;Bialic-Murphy et al, 2017). While it is likely that the distinction between short-and long-term dynamics is particularly important for assessing the likely outcome of plant reintroductions with artificially skewed stage structures, there is a dearth of demographic studies on this topic (but see, Wong and Ticktin, 2015).…”