Jalene M. LaMontagne

The functional response of a hoarding seed predator to mast seeding.

Mast seeding involves the episodic and synchronous production of large seed crops by perennial plants. The predator satiation hypothesis proposes that mast seeding maximizes seed escape because seed predators consume a decreasing proportion of available seeds with increasing seed production. However, the seed escape benefits of masting depend not only on whether predators are satiated at high levels of seed production, but also on the shape of their functional response (type II vs. type III), and the actual proportion of available seeds that they consume at different levels of seed production. North American red squirrels (Tamiasciurus hudsonicus) are the primary vertebrate predator of white spruce (Picea glauca) mast seed crops in many boreal regions because they hoard unopened cones in underground locations, preempting the normal sequence of cone opening, seed dispersal, and seed germination. We document the functional response of cone-hoarding by red squirrels across three non-mast years and one mast year by estimating the number of cones present in the territories of individual red squirrels and the proportion of these cones that they hoarded each autumn. Even though red squirrels are not constrained by the ingestive and on-body (fat reserves) energy reserve limitations experienced by animals that consume seeds directly, most squirrels hoarded < 10% of the cones present on their territories under mast conditions. Cone availability during non-mast years also reached levels that satiated the hoarding activity of red squirrels; however, this occurred only on the highest-quality territories. Squirrels switched to mushroom-hoarding when cone production was low and mushrooms were abundant. This resulted in type III functional response whereby the proportional harvest of cones was highest at levels of cone availability that were intermediate within non-mast years. Overall, more cones escaped squirrel cone-hoarding during a mast event than when cone production was low in non-mast years, which supports the predator satiation hypothesis. However, the highly variable seed escape in non-mast years may help to explain why all spruce cone production is not concentrated into fewer, larger, mast years.

Persistent maternal effects on juvenile survival in North American red squirrels

Maternal effects can have lasting fitness consequences for offspring, but these effects are often difficult to disentangle from associated responses in offspring traits. We studied persistent maternal effects on offspring survival in North American red squirrels (Tamiasciurus hudsonicus) by manipulating maternal nutrition without altering the post-emergent nutritional environment experienced by offspring. This was accomplished by providing supplemental food to reproductive females over winter and during reproduction, but removing the supplemental food from the system prior to juvenile emergence. We then monitored juvenile dispersal, settlement and survival from birth to 1 year of age. Juveniles from supplemented mothers experienced persistent and magnifying survival advantages over juveniles from control mothers long after supplemental food was removed. These maternal effects on survival persisted, despite no observable effect on traits normally associated with high offspring quality, such as body size, dispersal distance or territory quality. However, supplemented mothers did provide their juveniles an early start by breeding an average of 18 days earlier than control mothers, which may explain the persistent survival advantages their juveniles experienced.

Linking intraspecific variation in territory size, cone supply, and survival of North American red squirrels

Abstract In territorial species, competitive asymmetries can result in the uneven distribution of food resources as high-quality individuals force young or subordinates to occupy smaller or lower-quality sites, or both. However, spatiotemporal variation in the production of resources also can influence an individuals ability to monopolize resources and, consequently, affect survival. We examined how spatial and temporal variation in food supply affects the distribution of resources among territorial food-hoarding red squirrels (Tamiasciurus hudsonicus) by mapping cone production over 62.5 ha of white spruce (Picea glauca) forest and measuring the interrelationships between territory size, cone supply, and survival during 4 years of low cone abundance in Yukon, Canada. Territory size and cone production within a territory varied 10- and 520-fold, respectively, with juvenile squirrels occupying smaller territories with fewer cones. Because of small-scale heterogeneity in the distribution of cones, territory size explained low to moderate amounts of the variation in territory-wide cone production within (rs = 0.49–0.69) and across (rs = 0.31) years. Furthermore, spatial heterogeneity in cone production varied across years such that territory location was not useful for predicting relative food availability from one year to the next. Perhaps as a consequence of this heterogeneity, the number of cones within an individuals hoard was only weakly correlated with territory size (rs = 0.42) and not correlated with territory-wide cone production. Hoard size better predicted overwinter survival than did territory size, whereas cone production on a territory was not predictive of survival. We suggest that caution be used in equating territory size with food supply because small-scale spatial heterogeneity can weaken this relationship, particularly in food-hoarders. Spatiotemporal variation in food abundance, in turn, may cause high-quality territories in one year to be low-quality territories in other years, which will limit the ability of individuals to assess the long-term quality of territories at the time of settlement.

Tree cavity availability across forest, park, and residential habitats in a highly urban area

Tree cavities are used by a wide variety of species for nesting, food storage, and cover. Most studies on cavity availability have been conducted in forests, and little is known about urban areas. With urbanization, species that excavate cavities may be less abundant, natural tree-decay processes are managed, and tree densities are reduced, all of which may influence tree-cavity availability. We investigated three questions: 1) What is the prevalence of tree cavities in different habitats in the Chicago area? 2) How do the characteristics of natural and woodpecker-excavated cavities and cavity-trees differ across habitats? 3) How does the urban landscape influence the prevalence of tree cavities? We tested the capacity for large urban parks and residential areas to provide tree cavities at levels similar to forested areas. We surveyed 1,545 trees in these three habitats for excavated and natural (caused by decay) cavities. Cavities were most available in forests, where the density of trees was highest. We found that a similar proportion of trees in forests and parks had excavated cavities, but excavated cavities were rare in residential areas. Trees containing cavities were larger than control trees and had more decay, and excavated cavities were in larger trees with more decay than natural cavity trees. Canopy cover was the main landscape variable influencing excavated cavity availability. Our results suggest that the prevalence of tree cavities may not be a limiting factor for urban wildlife, however that is contingent on the levels of use of natural cavities, which is currently unknown.

Inter-annual variation in seed production has increased over time (1900–2014)

Mast seeding, or masting, is the highly variable and spatially synchronous production of seeds by a population of plants. The production of variable seed crops is typically correlated with weather, so it is of considerable interest whether global climate change has altered the variability of masting or the size of masting events. We compiled 1086 datasets of plant seed production spanning 1900–2014 and from around the world, and then analysed whether the coefficient of variation (CV) in seed set, a measure of masting, increased over time. Over this 115-year period, seed set became more variable for plants as a whole and for the particularly well-studied taxa of conifers and oaks. The increase in CV corresponded with a decrease in the long-term mean of seed set of plant species. Seed set CV increased to a greater degree in plant taxa with a tendency towards masting. Seed set is becoming more variable among years, especially for plant taxa whose masting events are known to affect animal populations. Such subtle change in reproduction can have wide-ranging effects on ecosystems because seed crops provide critical resources for a wide range of taxa and have cascading effects throughout food webs.

Variation and synchrony of tree species mast seeding in an old-growth temperate forest

Questions Mast seeding, synchronous highly variable seed production among years, occurs in many perennial plant species and across diverse plant communities. Two predominant ultimate hypotheses for mast seeding are pollination efficiency and predator satiation, with weather conditions as a proximate cause. Little consensus has been achieved regarding the relative impacts of ultimate selection and proximate weather on variation in seed production. Moreover, mast-seeding studies often focus on a single species or phylogenetically closely related species, while studies on plant communities consisting of tree species with a diversity of reproductive strategies are less common. Location The 25-ha Changbaishan temperate forest dynamic plot, Northeast China. Methods We used eight-years of seed rain data to characterize the patterns and evaluate underlying selective drivers of mast seeding. We employed generalized linear mixed-effects models to analyze the relationships between interannual variability of mast seeding and weather conditions. Results All 20 species in this forest community exhibited high variability in annual seed production, but the magnitude of seed production among species was generally asynchronous across years. Wind-pollinated species had higher interannual variation of seed production than animal-pollinated species, while species dispersed by seed predators and abiotic modes (e.g., wind and gravity) showed little variation. Species responded individually to weather conditions for both temperature and precipitation, and spring phenology at the same year as seed production had a larger effect among species than both the weather conditions of the same summer and season-long lags. Conclusions Our findings suggest that pollination efficiency hypothesis hada much stronger effect than predation satiation hypothesis on mast seeding, and weather conditions showed the proximate role of weather drivers in producing the community-wide mast seeding pattern. We emphasize the necessity to simultaneously assess drivers of mast seeding for multiple species within a plant community. This article is protected by copyright. All rights reserved.