Delayed effects of climate on vital rates lead to demographic divergence in Amazonian forest fragments

Deforestation often results in landscapes where remaining forest habitat is highly fragmented, with remnants of different sizes embedded in an often highly contrasting matrix. Local extinction of species from individual fragments is common, but the demographic mechanisms underlying these extinctions are poorly understood. It is often hypothesized that altered environmental conditions in fragments drive declines in reproduction, recruitment, or survivorship. The Amazon basin, in addition to experiencing continuing fragmentation, is warming and experiencing changes in precipitation leading to altered frequency and intensity of droughts and unusually wet periods. Whether plant populations in tropical forest fragments are particularly susceptible to extremes in precipitation remains unclear. Most studies of plants in fragments are relatively short (1-6 years), focus on a single life-history stage, and often do not compare to populations in continuous forest. Even fewer studies consider delayed effects of climate on demographic vital rates despite the importance of delayed effects in studies that consider them. Using a decade of demographic and climate data from an experimentally fragmented landscape in the Central Amazon, we assess the effects of climate on populations of an understory herb (Heliconia acuminata, Heliconiaceae). We used distributed lag non-linear models to understand the delayed effects of temperature and precipitation on survival, growth, and flowering. We detected delayed effects of climate up to 36 months. Drought two dry seasons prior to the February census decreased survival and increased flowering probability while drought in the wet season a year prior to the census decreased flowering probability and increased growth. The effects of extremes in precipitation on survival and growth were more pronounced in forest fragments compared to continuous forest. The complex delayed effects of climate and habitat fragmentation in our study point to the importance of long-term demography experiments in understanding the effects of anthropogenic change on plant populations.

Size-Dependent Flowering in relation to Grazing in a Short-Lived Monocarpic Perennial

In short-lived monocarpic perennials flowering probability depends on size and relative growth. Reproducing at a smaller size results in a higher prereproductive survival and shorter generation time but also may lead to lower fecundity. Conversely, reproducing at a larger size allows greater fecundity but leads to higher mortality during the prolonged vegetative period. Herbivory may influence the above described relationships via alterations in size at reproduction and survival. Here we use field data to explore in detail the reproduction of the short-lived monocarpic perennial C. vulgare under seasonal grazing. Vegetative plants were marked in paddocks with and without winter grazing, and their size, growth, and flowering status were recorded during a growing season in a field grazing experiment. Grazing increased both survival of vegetative plants and flowering probability, but it did not affect flowering size. The increase in flowering probability is a result of differential plant growth and size and may be related to greater resource availability, including light (necessary for flowering induction in C. vulgare) in grazed paddocks.

Variation in size-dependent fitness components in a terrestrial orchid, Dactylorhiza majalis (Rchb.) Hunt et Summerh., in relation to environmental factors

We investigated the flowering probability and flower production in relation to plant size in a terrestrial orchid, <em>Dactylorhiza majalis</em> at 10 meadow sites in central and southwestern Poland. These sites differed in altitude (low, high) and management (presence or absence of mowing). At all sites, concentrations of nutrients in the soil were also measured. The probability of flowering increased significantly with the size of the plant in all populations, indicating that individuals do not flower until they reach a threshold size. Populations at high altitudes and the unmown sites had significantly lower threshold sizes for reproduction and showed sharp increase in flowering probability with plant size, compared to other populations. The threshold sizes for reproduction tended to decrease at sites rich in N and Mg and poor in P and S. Flower production was also size-dependent in all populations. Considerable between-site differences were found in the slope and the intercept of the regression between plant size and flower production. Flower production at some sites, at high altitudes, increased more steeply with plant size than at other sites. However, no pattern in size-dependent flower production was found relative to the measured environmental variables. Most of the size-dependent components of flowering probability were related to each other but not with the size-dependent flower production.