For Endangered Species Day 2018, Pedro Quintana Ascencio and Eric Menges have written a blog post about their recently published paper on the population dynamics of Hypericum cumulicola, an endangered herb across a range of landscape drivers.

We are convinced that limited spatial replication and short study intervals can hinder our ability to adequately understand and predict population dynamics. For example, the effects of disturbance regimes on population dynamics can be challenging to study because of the large amount of longitudinal data required. Long-term studies may be necessary to avoid misleading conclusions built on chronosequence-based short-term studies. Even when such long-term data are available, decoupling the effects of time since disturbance from year and population effects (e.g. climate, biotic interactions) requires datasets with replication across space and time.

Fruits and flowers of Hypericum cumulicola (credit: Reed Bowman).

In our study published in Journal of Ecology (Quintana-Ascencio et al. 2018) we used an unusually detailed, spatially expansive, long-term dataset to unravel complex interactions between landscape patterns and ecological disturbances affecting the distribution and demography of Hypericum cumulicola, a pyrogenic and endangered plant species endemic to Florida.

We took advantage of an ongoing 22 year study that monitored populations in 15 independent habitat patches with a rich disturbance history (14 independent fires), well-described habitat requirements (for open gaps in Florida scrub dominated by Ceratiola ericoides), and a strong spatially patterned landscape.

Vegetative growth of Hypericum cumulicola during spring months (credit: Pedro Quintana-Ascencio).

Overall, our results indicated the importance of metapopulation dynamics. H. cumulicolaoccupancy and predicted population growth were highest in large, aggregated habitat patches. Large habitat patches may have several advantages for metapopulation dynamics, including a larger target for rescues, greater diversity of microhabitats, and the ability to support larger populations less prone to demographic or environmental stochasticity (Hanski, Moilanen & Gyllenberg, 1996).

Model predictions of abundance were most reliable for patches with the extremes of patch area or aggregation. These results indicate that limited dispersal and unfavorable matrix habitats can synergistically contribute to colonization failure. Few studies have integrated population models and landscape level environmental drivers to characterize species distributions, although this approach has great promise for assessing the consequences of environmental changes.

View of the Florida Rosemary scrub at Archbold Biological Station (credit Reed Bowman).

The distribution of species across landscapes ultimately reflects the interaction of demography with landscape and disturbance properties. However, both demographic inertia (e.g., long life span, dormant stages) and landscape history (e.g. environmental legacies) may create lags in responses. Therefore, realized species distributions (reflecting past interactions) may have different patterns than current vital rates.

H. cumulicola occupancy peaked at higher elevations in larger patches but many vital rates peaked at lower elevations. This may reflect lags in demography such as the role of seed banks in allowing populations to persist between disturbances. This demographic ghost of mortality past may explain unexpected demographic patterns in chronosequence studies. Many critiques of demographic modeling have pointed out that models do a poor job of predicting beyond more than a few years (Crone, 2013). By incorporating common drivers such as weather, habitat suitability, disturbances, landscape patterns, and land management, we can improve our understanding of temporal and spatial variability in demography (Ehrlén & Morris, 2015).

Pedro F Quintana Ascencio (University of Central Florida, USA) and Eric S Menges (Archbold Biological Station, USA)

This blog post is part of a series of blog posts from the BES journals for Endangered Species Day 2018. Read our other Endangered Species blog posts here:

Journal of Animal Ecology: The intersection of wildlife conservation, disease, and human health 

Journal of Applied Ecology: Stress on the ski slope: individual capercaillies show different coping styles