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

Abstract

We carried out a posthurricane evaluation of Broughtonia cubensis (Lindl.) Cogn., an endemic Cuban epiphytic orchid, after Hurricane Ivan (2004). We studied the transient responses in the stochastic dynamics of the species at three different sites over 13 successive years (2006–2019), monitored plot inventories (464 individuals in 10 transects) and built stochastic population models. The deterministic stochastic growth rate values (λ) did not significantly differ (F = 2.76; p>0.076) among the three sites over the 2006–2019 period. The long-term stochastic growth rate was λs ¼ 0.973 [0.932, 1.034]. The matrix elements that had the largest effect on λ were the transition to and stasis within the largest size class. Transient responses explained an average of 86% of the variation in the observed population growth rates R2 for rTD vs:robs ð Þ, compared to 4% of the variation in the vital rates R2 for rVR vs:robs ð Þ. Because transient dynamics are dependent on the population size composition, we ran extinction risk analyses under two scenarios: a population composed mainly of juveniles and another composed mainly of adults. There was little risk of falling below the quasi-extinction threshold before 25 year for both juveniles and adults. However, the risk of quasi-extinction was almost certain for both size classes by 80 year. We also simulated the effect of increasing the hurricane occurrence probability over 80 year on the population. There was little risk of extinction before 20 year in the baseline model, but there was a significant risk of extinction within 5 year when 90% of the individuals were affected by a new hurricane event.