Reproductive efficiency and shade avoidance plasticity under simulated competition

Plant strategy and life‐history theories make different predictions about reproductive efficiency under competition. While strategy theory suggests under intense competition iteroparous perennial plants delay reproduction and semelparous annuals reproduce quickly, life‐history theory predicts both annual and perennial plants increase resource allocation to reproduction under intense competition. We tested (1) how simulated competition influences reproductive efficiency and competitive ability (CA) of different plant life histories and growth forms; (2) whether life history or growth form is associated with CA; (3) whether shade avoidance plasticity is connected to reproductive efficiency under simulated competition. We examined plastic responses of 11 herbaceous species representing different life histories and growth forms to simulated competition (spectral shade). We found that both annual and perennial plants invested more to reproduction under simulated competition in accordance with life‐history theory predictions. There was no significant difference between competitive abilities of different life histories, but across growth forms, erect species expressed greater CA (in terms of leaf number) than other growth forms. We also found that shade avoidance plasticity can increase the reproductive efficiency by capitalizing on the early life resource acquisition and conversion of these resources into reproduction. Therefore, we suggest that a reassessment of the interpretation of shade avoidance plasticity is necessary by revealing its role in reproduction, not only in competition of plants.     

Populations evolving towards failure: costs of adaptation under competition at the range edge of an invasive perennial plant

Background: Species undergoing range expansion adapt to novel and stressful environments at range fronts. These adaptations of the edge populations may incur fitness costs. These costs may play a crucial role in stopping range expansion before absolute physiological and evolutionary limits were reached. Costs however have proven to be elusive. These may be specifically expressed under competition.

Aims: Here, we assessed the costs of adaptation in range-edge populations of an invasive plant by evaluating plant responses under competition.

Methods: We grew plants from range-centre and edge populations under competition treatments in a glasshouse. We predicted that plants from the range-edge would express lower reproductive efficiency under competition compared with centre population plants, and this would indicate a potentially maladaptive response.

Results: Under high competition, plants from the range-edge expressed lower reproductive efficiency relative to range-centre plants which supported our prediction. In addition, they were more heavily affected by competition.

Conclusions: Adaptation to novel environments at the range-edge has incurred a cost as a potentially maladaptive response under competition, which may contribute to the formation of the range-edge. This finding suggests that these costs likely form part of the classic trade-offs involved with stress-tolerance and may have effects on range evolution.     

Testing specialization hypothesis on a stress gradient

Specialization can allow plants to perform well in their home environments at the expense of poor performance in other habitats. A great difference in performance across habitats is observed as high phenotypic plasticity in performance traits and a by‐product of selection. However, phenotypic plasticity (particularly adaptive plasticity) can be an active response to the selection by allowing the maintenance of performance. Therefore, specialization and adaptive plasticity delineate two opposing strategies. The specialization hypothesis presents a non‐adaptive interpretation of plasticity and predicts that phenotypic plasticity of performance traits is greater in specialization to good habitats, whereas bad habitat specialists express low plasticity in performance traits. We tested the specialization hypothesis using plants adapted to extremely stressful mine‐site habitats (sites with highly acidic soil and heavy metal contamination). Seeds of five herbaceous species were collected from high stress (mine site) and low stress habitats. We established a glasshouse experiment where seedlings from high and low stress habitats were grown under near neutral pH and acid soil treatments. We compared performance trait plasticity (e.g. biomass) from high stress and low stress populations and found that there was no significant difference in performance traits between high and low stress populations across treatments. The overall result did not support the specialization hypothesis. Moreover, our results suggest that the species invaded the mine sites are either extreme generalists or the surrounding populations retain some stress tolerant genotypes that are capable of invading the mine sites.     

Latitudinal shifts in mangrove species worldwide: evidence from historical occurrence records

Consequences of global climate change on mangrove habitats are ambiguous owing to multifaceted factors. In this study, we examined historical occurrences of ten common mangrove species and quantified the rate of latitudinal shift as a possible response to climate change. The Global Biodiversity Information Facility (GBIF) was used to gather occurrence of mangrove species. We found that nine of ten species have been shifting poleward since the 1950s. Overall mean latitudinal shift rates of mangrove species were significantly higher in Australia than in North America (1.7 and 1.3 latitude degrees per decade, respectively). In Australia, mean temperature and precipitation of localities decreased as mangrove species shifted towards drier regions at higher latitudes. However, in North America and West Africa, mean temperature of localities seems relatively stable, whereas precipitation slightly decreased. We provide new quantitative information on shifts in occurrence of common mangrove species worldwide under a changing climate. We confirm the poleward movement of mangrove species over the past 70 years and suggest that local mean temperature and precipitation can act as key drivers of mangrove range shifts. We also advise that poleward latitudinal shifts in mangrove species should be taken into account when establishing new nature reserves.