Sticking around: Plant persistence strategies on edaphic islands

Abstract

Aim Species on islands are at high risk of extinction due to environmental changes, including global warming, land‐use alterations and invasions. At local scales, extinctions can be offset by strategies promoting in situ persistence. We explored how persistence‐related traits of plants—that is, linked to belowground resource conservation, growth, size and longevity—on edaphic islands respond to variation in insularity and the environment (soil and microclimate), including intraspecific variability, which is rarely considered in functional island biogeography. We hypothesised that plants facing strong insularity and harsh soil conditions are characterised by enhanced persistence abilities. Location Shallow‐soil temperate dry grasslands on granite outcrops, Central Europe. Methods We focussed on edaphic island specialist species belonging to different life histories, namely clonal and non‐clonal perennial plants. We used linear and linear mixed‐effect models to examine intra‐ and interspecific trait patterns versus variation in insularity, soil and microclimate. Results Insularity tended to promote smaller plants (non‐clonal species) and belowground resource‐conservative strategies (both clonal and non‐clonal species), increasing the likelihood of local persistence. Soil also contributed largely to explaining persistence‐related trait patterns: plants growing in harsh soil conditions tended to be resource conservative. Clonal species are distinguished by highly consistent responses to variation in insularity and soil conditions, whereas non‐clonal plants showed distinct species‐specific responses. Main conclusions Our findings have important implications for the conservation biogeography of edaphic island plant specialists. Clonal species may be susceptible to local extinction should insularity or soil conditions vary, for example, due to abrupt changes in the geographical setting (e.g. habitat loss) or local environmental factors (e.g. N‐deposition). Non‐clonal species may instead face environmental changes differently; some will go extinct, whereas others will survive, depending on the prevailing abiotic pressures. This seems to challenge previous views that predicted clonal species to be the winners and non‐clonal species the losers against local extinction.

Trash or treasure: Rhizome conservation during drought

“…All plants produced more new rhizomes and above‐ground biomass from younger rhizome parts than older rhizome parts and all plants increased rhizome dry matter content (BODMC). BODMC may be very sensitive to water availability both intraspecifically and interspecifically (Ottaviani et al, 2022) and this trend represents a similar conservative strategy to the above‐ground plant parts (e.g. leaf dry matter content; Wright et al, 2004).…”

Approaching inselberg biodiversity conservation through plant growth and dispersal strategies

“…The clustering strategy can be more advantageous than risking energy overexpenditure on unnecessary long dispersal events to sites where they cannot survive and maintain gene flow (Schenk, 2013). In many cases, edaphically specialist plants exhibit persistence‐related traits in order to ensure their survival in such environments (Ottaviani et al, 2022). In this case, we suggest that the production of numerous and small seeds by lithophytes might be related to conservative resource use (e.g., metabolic cost vs. resource availability, Hughes et al, 1994), rather than explained by an escape hypothesis to avoid density‐dependent mortality ( sensu Howe & Smallwood, 1982).…”

“…They are characterized by habitats whose productivity is constrained by environmental factors, such as drought, due to particular edaphic and topographic features (Porembski, 2007;de Paula et al, 2015;Eibes et al, 2022). That would mean that species that occur in inselbergs' habitats are more exposed to external constraints and are likely to exhibit ecological strategies that would ensure survival at the cost of their growth (de Paula et al, 2015(de Paula et al, , 2019Ottaviani et al, 2022). Moreover, inselbergs display a diverse and endemic-rich flora with populations that are often isolated (Porembski & Barthlott, 2000;Hmeljevski et al, 2017;de Paula et al, 2020) and threatened by multiple human activities (e.g., plant overharvesting, biological invasion, fire; Porembski et al, 2016;de Paula et al, 2020).…”

“…Improving our understanding of such trade‐offs is especially relevant for islands or island‐like communities, in which environmental constraints and isolation play a more important role in the species assembly. For instance, some species from islands/island‐like communities show strategies to avoid local extinction, including conservative resource use to cope with ecological challenges and traits related to regeneration processes that increase plant persistence (Ottaviani et al, 2022). Although such strategies make those plants remarkably fit for islands/island‐like conditions, human‐driven environmental changes might take place at greater magnitudes and faster pace than species can cope with, leaving plants with high habitat specificity and lower dispersal capacity with “nowhere to go” (Loarie et al, 2009; Dawson et al, 2011).…”

Growing old while staying young

“…However, this strategy also has limitations over long periods of time. Clonal plants form sessile, genetically homogeneous communities confined to specific areas, and changes in local environmental conditions that inevitably occur over millennia may exceed their adaptive potential (Ottaviani et al, 2022 ).…”