Estimating vital rate variation to assess early success of scrub mint translocations

Abstract

Species translocations are increasingly common in rare plant conservation.Wild populations can provide basic ecological knowledge to improve their chance of success. In the heavily fragmented Florida scrub, USA, many listed species require translocations to persist, including Dicerandra christmanii. In 1994, we began monitoring the only protected population of D. christmanii growing both in gaps (open areas) within the shrub matrix and on roadsides.In 2010, we augmented this population by adding plants and seeds to unoccupied gaps. In 2012, we introduced plants to a separate protected site to create a new population. We evaluated early translocation success using generalized linear mixed-effect models of vital rate variation among habitat types. Survival probability increased with size, peaking at 0.6-0.8, and was lowest in augmentations and highest in introductions. Growth increased with plant size across all habitat types, except for the largest adults which experienced senescence.Naturally recruited plants in gaps showed the highest reproduction probability and fecundity at smaller sizes, but larger plants in translocations had the highest fecundity. Yearling recruitment was higher in translocated plants relative to naturally recruited plants in gaps during the initial years following outplanting. Experimental components of translocations also affected outplanting performance with positive effects of fire. These analyses suggest a high potential for translocations to become established and contribute to species recovery.

Leveraging projection models to evaluate long‐term dynamics of scrub mint translocations

“…In tandem with the companion manuscript (Koontz et al, 2023), our results paint a complex picture of translocation dynamics and suggest likely reasons for the often-observed long-term failure of initially successful translocation efforts (Godefroid et al, 2011). For D. christmanii, vital rate estimates indicate initial translocation success, with values for introductions as strong or stronger than those for natural populations (Koontz et al, 2023). This might be partially explained by the vigor of the plants used in outplanting, which were grown in more favorable greenhouse conditions, and short-term actions including small scale disturbances and initial irrigation.…”

“…Dicerandra christmanii has been recorded in fewer than 10 sites (FNAI, 2010) with only one population in a protected site: the Flamingo Villas (FV) unit of the Lake Wales Ridge National Wildlife Refuge (LWRNWR), which is managed by the US Fish and Wildlife Service (USFWS). More detailed descriptions on the species can be found in the companion manuscript (Koontz et al, 2023).…”

“…We obtained fruits-per-branch counts in late 2019 from both FV and CC. Additional information on data collection can be found in Koontz et al (2023).…”

“…We recognized three life history stages-seed, yearling (new plant that survives to its first census), and adult-and used the natural logarithm of individual number of branches as the continuous state variable, with a quadratic response for survival. In a companion manuscript, we modeled vital rate variation using generalized linear mixed models (Koontz et al, 2023). We used binomial error distributions and logit link for survival (σ), probability of reproduction (φ0), and proportion of reproductive branches (φ1).…”

“…In a companion paper, we used Bayesian methods to compare vital rate variation of Dicerandra christmanii across five types of populations, including natural and translocated populations in different habitats (Koontz et al, 2023). Our goal here was to combine these vital rates into IPMs and evaluate differences in the population dynamics of D. christmanii across the different population types.…”