Sheltered from the storm? Population viability analysis of a rare endemic under periodic catastrophe regimes

Abstract

Rare species are important targets for biodiversity conservation efforts because rarity often equates to small populations and increased endangerment. Rare species are prone to stochastic extinction events and may be particularly susceptible to catastrophes. Therefore, understanding how rare species respond to disturbances is critical for evaluating extinction risk and guiding conservation managers. Population viability analyses (PVAs) are essential for assessing rare species' status yet they seldom consider catastrophic events. Accordingly, we present a PVA of a rare tropical epiphyte, Lepanthes caritensis (Orchidaceae), under simulated disturbance regimes to evaluate its demographics and extinction risk. We aimed to test how demographic models incorporating catastrophes affect population viability estimates. Our goal was to better guide management of these orchids and other rare plants. Results revealed L. caritensis numbers have declined recently, but projected growth rates indicated that most subpopulations should increase in size if undisturbed. Still, projection models show that moderate catastrophes reduce growth rates, increase stochasticity in subpopulation sizes, and elevate extinction risk. Severe catastrophes had a more pronounced effect in simulations; growth rates fell below replacement level, there was greater variation in projected population sizes, and extinction risk was significantly higher. PVAs incorporating periodic catastrophes indicate that rare species may have greater extinction probabilities than standard models suggest. Thus, precautionary conservation measures should be taken in disturbance prone settings and we encourage careful monitoring after environmental catastrophes. Future rare plant PVAs should incorporate catastrophes and aim to determine if rescue and reintroduction efforts are necessary after disturbances to insure long-term population viability.

Toward a more temporally explicit framework for community ecology

“…While it could be difficult to distinguish between these two mechanisms (Schroder, Persson, & De Roos, ), the persistence of effects on ecologically meaningful timescales can often be observed directly. These include persistent changes in habitat (e.g., Brokaw & Grear, ; del Arroyo & Silver, ; Lloren, Fahrig, Bennett, Contreras, & McCune, ); organismal traits (e.g., Hunter & Forkner, ; Little, Fisher, Schoener, & Pruitt, ; Siegle et al, ; Spiller & Agrawal, ); the abundance or distribution of organisms (e.g., Spiller & Schoener, ; Wernberg et al, ); community composition via invasion or extinction (e.g., Davis et al, ; McKechnie & Wolf, ; Nowicki et al, ); the frequency or intensity of the perturbation regime itself (e.g., Crain, Tremblay, & Ferguson, ; Parmesan et al, ). These are certainly not exclusive mechanisms, and many event‐driven dynamics reflect the combined effects of multiple dynamic processes.…”

The effects of hurricanes on the stochastic population growth of the endemic epiphytic orchid Broughtonia cubensis living in Cuba

“…Ecologists have been using population projection models to derive management policies for more than 40 year (Crone et al, 2011;Crone et al, 2013). The usual emphasis of these matrix models has been on asymptotic behavior, but due to the formulation of some transient indices (Neubert & Caswell, 1997;Stott, Townley, & Hodgson, 2011), it has become possible to investigate short-term population dynamics that occur due to disturbances (Crain, Tremblay, & Ferguson, 2019).…”

“…Over the last 30 years, 27 hurricanes have affected the behavior and survival of epiphytic orchid populations in this region to various degrees (Tremblay, 2008). The increasing frequencies and intensities of hurricanes could change plant population dynamics, altering their survival, growth, and fitness (Crain et al, 2019;Tanner, Rodriguez-Sanchez, Healey, Holdaway, & Bellingham, 2014).…”

“…In these changing environments, matrix stochastic formulations seem to be an adequate approach to studying the population dynamics of these species (Tuljapurkar, 1982;Tuljapurkar, Gaillard, & Coulson, 2009;Tuljapurkar, Horvitz, & Pascarella, 2003); the usual focus of these models has previously been on asymptotic dynamics, and only recently has the role of short-term dynamics been explored using different transient indices (Caswell, 2007;Crain et al, 2019;Ellis, 2013;Jelbert et al, 2019;McDonald, Gann, Jonson, & Dixon, 2016;Stott, 2016;Tremblay, Ravent os, & Ackerman, 2015).…”

Environmental and Management Effects on Demographic Processes in the U.S. Threatened Platanthera leucophaea (Nutt.) Lindl. (Orchidaceae)

“…ex Rolfe., populations in Cuba indicate that hurricane frequencies of 0.14 and above greatly increase the chance of population extinction [ 64 ]. Simulations also indicate that extinction risk increases with increasing hurricane severity for Lepanthes caritensis Tremblay & Ackerman in Puerto Rico [ 65 ].…”