scholarly journals Seed masting causes fluctuations in optimum litter size and lag load in a seed predator

2018 ◽  
Author(s):  
Andrew McAdam ◽  
Stan Boutin ◽  
Ben Dantzer ◽  
Jeff Lane
Keyword(s):  
Litter Size ◽  
Picea Glauca ◽  
Life Histories ◽  
Local Density ◽  
White Spruce ◽  
Tamiasciurus Hudsonicus ◽  
Seed Predator ◽  
Red Squirrels ◽  
Seed Predators ◽  
Seed Crops

The episodic production of large seed crops by some perennial plants, is referred to as masting and is known to increase seed escape by alternately starving and swamping seed predators. These pulses of resources, however, might also act as an agent of selection on the life histories of seed predators, which could indirectly enhance seed escape by inducing an evolutionary load on seed predator populations. Lag loads in seed predators could result from mast-induced shifts in optimum phenotypes that exceed the capacity of seed predators to adaptively track optimum phenotypes through phenotypic plasticity. Alternatively, masting could generate mismatches in selection across generations, where adaptation to the parental environment leads to maladaptation in the offspring environment. Here we measured natural selection on female North American red squirrels (Tamiasciurus hudsonicus) across 28 years and five white spruce (Picea glauca) masting events. Red squirrel litter sizes were similar to optimum litter sizes during non-mast years, but were well below optimum litter sizes during resource-rich mast years. Mast events, therefore caused selection for larger litters (B = 0.25) and a lag load (L = 0.25) on red squirrels during mast years. Furthermore, we found that the annual fitness of spruce trees was negatively related to the local density of squirrels during mast years, indicating that the observed lag load on squirrels enhanced the number of spruce cones escaping squirrel predation. Although, the frequency of mast events and the demography of red squirrels were such that offspring and parents often experienced opposite environments with respect to the mast, we found no effect of environmental mismatches across generations on either offspring survival or population growth. Instead, squirrels plastically increased litter sizes in anticipation of mast events, which partially, although not completely, reduced the lag load resulting from this change in food availability. Variable selection on litter size caused by white spruce mast events, therefore, induced a lag load on the population of red squirrels that was not affected by whether individual squirrels were born during mast (matching) or non-mast (mismatching) conditions.

Pre-dispersal seed predation of white spruce cones in logged boreal mixedwood forest

2003 ◽  
Vol 33 (1) ◽  
pp. 33-40 ◽  
Author(s):  
Susan Peters ◽  
Stan Boutin ◽  
Ellen Macdonald
Keyword(s):  
Seed Predation ◽  
Picea Glauca ◽  
Natural Regeneration ◽  
White Spruce ◽  
Tamiasciurus Hudsonicus ◽  
Red Squirrels ◽  
Tree Crowns ◽  
Tree Retention ◽  
Boreal Mixedwood Forest ◽  
Mixedwood Boreal Forest

Predation of white spruce (Picea glauca (Moench) Voss) cones by red squirrels (Tamiasciurus hudsonicus Erxleben) was quantified in the mixedwood boreal forest of Alberta in cutblocks with seed tree retention and in adjacent uncut forest, during 3 years with varying levels of cone crop (1998, 1999, 2000). Percent cone loss was quantified by comparison of paired pre- and post-caching photographs of tree crowns. Cone loss from seed trees in cutblocks was significantly lower than from control trees in adjacent uncut forest (48.5 vs. 54.9%). Although the number of cones produced per tree declined by 42% and the percentage of trees producing cones declined by approximately 48% between 1998 and 2000, there was no corresponding increase in the percentage of cones harvested by squirrels. Percent cone loss was significantly lower from single seed trees in cutblocks, as compared with seed trees left in patches of more than 20 trees (33.4 vs. 50.5%). Cone predation significantly reduced the amount of seed available for natural regeneration using a seed tree system. Although blowdown may be reduced if seed trees are left in patches, leaving white spruce seed trees as singles in cutblocks may reduce the level of cone predation.

VIABILITY OF WHITE SPRUCE SEED FROM SQUIRREL-CUT CONES

1964 ◽  
Vol 40 (1) ◽  
pp. 98-110 ◽  
Author(s):  
J. W. Bruce Wagg
Keyword(s):  
Picea Glauca ◽  
Seed Viability ◽  
White Spruce ◽  
Mature Seed ◽  
Tamiasciurus Hudsonicus ◽  
Red Squirrel ◽  
Red Squirrels

A study was made of the viability of white spruce, Picea glauca, seed obtained from seven cone caches of red squirrels, Tamiasciurus hudsonicus. Habits of the red squirrel, relation of seed viability to cone-caching activities and the relation of viability of seed obtained from the cached cones to the cones on the trees are described.Viability of see from cached cones does not vary between the time squirrels began to cache cones in quantity and the time the last cones are cached. Seed from the cached cones showed a higher percentage of viability than seed of cones collected from trees, because some of the mature seed had fallen from the partially open cones on the trees resulting in an increase in the percentage of undeveloped seed in progressive cone collections.

scholarly journals Individual variation in phenotypic plasticity of the stress axis

2019 ◽  
Author(s):  
Sarah Guindre-Parker ◽  
Andrew G. Mcadam ◽  
Freya Van Kesteren ◽  
Rupert Palme ◽  
Rudy Boonstra ◽  
...  
Keyword(s):  
Phenotypic Plasticity ◽  
Individual Variation ◽  
Local Density ◽  
Reaction Norm ◽  
Tamiasciurus Hudsonicus ◽  
Stress Axis ◽  
Red Squirrels ◽  
Conspecific Density ◽  
North American Red Squirrels ◽  
Future Work

ABSTRACTPhenotypic plasticity—one individual’s capacity for phenotypic variation under different environments—is critical for organisms facing fluctuating conditions within their lifetime. North American red squirrels (Tamiasciurus hudsonicus) experience drastic among-year fluctuations in conspecific density. This shapes juvenile competition over vacant territories and overwinter survival. To help young cope with competition at high densities, mothers can increase offspring growth rates via a glucocorticoid-mediated maternal effect. However, this effect is only adaptive under high densities, and faster growth often comes at a cost to longevity. While experiments have demonstrated that red squirrels can adjust hormones in response to fluctuating density, the degree to which mothers differ in their ability to regulate glucocorticoids across changing densities remains unknown—little is known about within-individual plasticity in endocrine traits relative to among-individual variation. Findings from our reaction norm approach revealed significant individual variation not only in a female red squirrel’s mean endocrine phenotype, but also in endocrine plasticity in response to changes in local density. Future work on the proximate and ultimate drivers of variation in the plasticity of endocrine traits and maternal effects is needed, particularly in free-living animals experiencing fluctuating environments.

scholarly journals Cone characteristics and insect predation levels vary across years in mast seeding white spruce

2021 ◽  
Author(s):  
Abigail C Leeper ◽  
Jalene M LaMontagne
Keyword(s):  
Seed Predation ◽  
Mixed Models ◽  
Linear Mixed Models ◽  
Population Level ◽  
White Spruce ◽  
Mast Seeding ◽  
Seed Predator ◽  
Cone Production ◽  
Insect Predation ◽  
Seed Crops

Populations of many tree species exhibit synchronous and highly temporally variable seed crops across years. This is called mast seeding, and there are two predominant hypotheses for this pattern of reproduction, pollination efficiency and seed-predator satiation. Mast seeding studies typically involve records of population-level reproduction, with less information on the characteristics of reproductive structures. Here, we use data across six years (2012-2017), spanning a range of population-level cone conditions, to characterize i) white spruce (Picea glauca) cone lengths and seeds per cone, and ii) levels of seed predation. We quantified population-level cone production and collected 1,399 cones from a total of 38 trees in the Huron Mountains, Michigan, USA. Linear mixed models showed that mean and minimum cone lengths varied significantly across years; both being longest during the greatest cone production year. Larger cones had more seeds and the slopes of the relationships as well as the intercepts varied significantly across years. Generalized linear mixed models and AIC model selection showed that cones with insect predation damage was greatest when population-level reproduction was the lowest, with a mean proportion of cones damaged 0.82 in that year. Our findings show that white spruce cone characteristics and losses to insect seed predation vary temporally, and follow expectations based on mast seeding hypotheses.

scholarly journals Individual variation in phenotypic plasticity of the stress axis

2019 ◽  
Vol 15 (7) ◽  
pp. 20190260 ◽  
Author(s):  
Sarah Guindre-Parker ◽  
Andrew G. Mcadam ◽  
Freya van Kesteren ◽  
Rupert Palme ◽  
Rudy Boonstra ◽  
...  
Keyword(s):  
Phenotypic Plasticity ◽  
Individual Variation ◽  
Local Density ◽  
Reaction Norm ◽  
Tamiasciurus Hudsonicus ◽  
Stress Axis ◽  
Red Squirrels ◽  
Conspecific Density ◽  
North American Red Squirrels ◽  
Future Work

Phenotypic plasticity—one individual's capacity for phenotypic variation under different environments—is critical for organisms facing fluctuating conditions within their lifetime. North American red squirrels ( Tamiasciurus hudsonicus ) experience drastic among-year fluctuations in conspecific density. This shapes juvenile competition over vacant territories and overwinter survival. To help young cope with competition at high densities, mothers can increase offspring growth rates via a glucocorticoid-mediated maternal effect. However, this effect is only adaptive under high densities, and faster growth often comes at a cost to longevity. While red squirrels can adjust hormones in response to fluctuating density, the degree to which mothers differ in glucocorticoid plasticity across changing densities remains unknown. Findings from our reaction norm approach revealed significant individual variation not only in a female red squirrel's mean endocrine phenotype but also in endocrine plasticity in response to changes in local density. Future work on proximate and ultimate drivers of variation in endocrine plasticity and maternal effects is needed, particularly in free-living animals experiencing fluctuating environments.

scholarly journals The Role of the American Red Squirrel (Tamiasciurus Hudsonicus) in the Evolution of Serotiny in Lodgepole Pine (Pinus Contorta).

2011 ◽  
Vol 33 ◽  
pp. 155-160
Author(s):  
Matt Talluto ◽  
Craig Benkman
Keyword(s):  
Pinus Contorta ◽  
Lodgepole Pine ◽  
Fire Frequency ◽  
Tamiasciurus Hudsonicus ◽  
Red Squirrel ◽  
Seed Predator ◽  
Red Squirrels ◽  
Factors Affecting ◽  
And Function ◽  
High Elevations

Coevolutionary interactions can have dramatic effects on the structure and function of ecosystems, particularly when spatial structure leads to local adaptation. Here we report on an ongoing study of the interaction between lodgepole pine and its primary pre-dispersal seed predator, the American red squirrel. Lodgepole pine is serotinous, meaning seeds are held in closed cones until released by the heat of a fire. Serotiny has been shown to increase seedling density following stand replacing fire, and can have far-reaching ecosystem- and community-level implications. Red squirrels are negatively associated with serotiny at broad geographic scales, and may select against the serotinous trait. This project aims to examine the correlation between red squirrel density and the frequency of serotiny in lodgepole pine forests and the mechanisms underlying potential selection against serotiny by red squirrels. Specifically, we will determine whether this correlation is present when other factors affecting serotiny (i.e., fire frequency, elevation) are held constant, whether the fitness of serotinous trees is reduced in the presence of red squirrels, and what factors control the density of red squirrels. Preliminary results indicate that serotiny and squirrel density is strongly negatively correlated, but only at low elevations. Serotiny was nearly absent at high elevations, but squirrel density varied as much as at low elevations, suggesting that serotiny does not control squirrel density, but that increasing squirrel density may lead to increasing selection against serotiny.

scholarly journals Potential of Small Culverts as Wildlife Passages on Forest Roads

2021 ◽  
Vol 13 (13) ◽  
pp. 7224
Author(s):  
Hsiang-Ling Chen ◽  
Erin E. Posthumus ◽  
John L. Koprowski
Keyword(s):  
Animal Movement ◽  
Small Dimension ◽  
Lynx Rufus ◽  
Tamiasciurus Hudsonicus ◽  
Red Squirrels ◽  
Forest Roads ◽  
Alternative Pathways ◽  
Slow Moving ◽  
Trail Cameras ◽  
Spermophilus Variegatus

Roads and traffic can cause animal mortality. Specifically, roads serve as barriers by impeding animal movement, resulting in demographic and genetic consequences. Drainage structures, such as culverts, can provide linkages between habitat patches. However, the potential of small culverts with diameters of <60 cm (e.g., wildlife passages that facilitate movement on forest roads) are relatively unknown. In this study, we used trail cameras to monitor the use of 14 small culverts, by mammals, along forest roads on Mt. Graham, home of the critically endangered Mt. Graham red squirrels (Tamiasciurus hudsonicus grahamensis), in southeastern Arizona, USA. From 2011 to 2013, we only recorded 20 completed road crossings through culverts. More than half of culvert uses were by striped skunks (Mephitis mephitis), followed by the rock squirrel (Spermophilus variegatus) and the bobcat (Lynx rufus). The Mt. Graham red squirrel was the only species that was common along the roads, but never crossed the roads. Culverts with higher usages were characterized by shorter culvert lengths and absence of accumulated soil inside the culverts. Our study shows that small-dimension drainage systems may provide alternative pathways for wildlife crossing roads, especially for slow moving and ground dwelling species. However, the potential of small culverts assisting wildlife crossings can only be maximized when culverts are accessible year-round.

WHITE SPRUCE AND THE SPRUCE BUDWORM: DEFINING THE PHENOLOGICAL WINDOW OF SUSCEPTIBILITY

1997 ◽  
Vol 129 (2) ◽  
pp. 291-318 ◽  
Author(s):  
Robert K. Lawrence ◽  
William J. Mattson ◽  
Robert A. Haack
Keyword(s):  
Picea Glauca ◽  
High Performance ◽  
Choristoneura Fumiferana ◽  
Spruce Budworm ◽  
White Spruce ◽  
Shoot Elongation ◽  
Larval Survival ◽  
Strongly Correlated ◽  
Negative Effect ◽  
Foliar Traits

AbstractSynchrony of insect and host tree phenologies has often been suggested as an important factor influencing the susceptibility of white spruce, Picea glauca (Moench) Voss, and other hosts to the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). We evaluated this hypothesis by caging several cohorts of spruce budworm larvae on three white spruce populations at different phenological stages of the host trees, and then comparing budworm performance with host phenology and variation of 13 foliar traits. The beginning of the phenological window of susceptibility in white spruce occurs several weeks prior to budbreak, and the end of the window is sharply defined by the end of shoot growth. Performance was high for the earliest budworm cohorts that we tested. These larvae began feeding 3–4 weeks prior to budbreak and completed their larval development prior to the end of shoot elongation. Optimal synchrony occurred when emergence preceded budbreak by about 2 weeks. Larval survival was greater than 60% for individuals starting development 1–3 weeks prior to budbreak, but decreased to less than 10% for those starting development 2 or more weeks after budbreak and thus completing development after shoot elongation ceased. High performance by the budworm was most strongly correlated with high levels of foliar nitrogen, phosphorous, potassium, copper, sugars, and water and low levels of foliar calcium, phenolics, and toughness. These results suggest that advancing the usual phenological window of white spruce (i.e. advancing budbreak prior to larval emergence) or retarding budworm phenology can have a large negative effect on the spruce budworm’s population dynamics.

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