Influence of variation in individuals, and spatial and temporal variation in resource availability on population dynamics. Jalene M. LaMontagne

Resource heterogeneity & Individual variation  Individual variation historically ignored in populations  Relatively recently, habitat heterogeneity & individual variation in performance gaining interest  Individual variation extremely difficult to quantify:  Resource availability  Performance

Areas of focus 1.Population dynamics (& individual variation) 2.Spatial (& temporal) patterns in resource heterogeneity (primarily cones, spruce beetle infestation) 3.Territoriality and territory quality (individual variation) Data-sources used 1.Midden census data 2.Juvenile / admums files 3.Cone production counts 4.Historical territory mapping plus… 1. Vegetation transects & maps created 2. Spatial variation in territory mapping 3. Additional cone counts

Thesis outline Chapter 1: Population dynamics of red squirrels. Chapter 2: Local dynamics of cone crop production by individual white spruce trees. Chapter 3: Factors influencing cone production by white spruce. Chapter 4: Determinants of territory size in red squirrels. Chapter 5: Resource acquisition, overwinter survival, and reproductive output of red squirrels, implications for individual variation on population dynamics. Chapter 6: Influence of individual variation in modelling population dynamics of a wild population.

Other papers 1.Cone crop conversion factor for individual white spruce trees. 2.Determining territory boundaries for red squirrels. 3.Spruce beetle spread? Collaborations 1. Cone crop conversion factor for individual white spruce trees. - w/ Sue Peters 2.Red squirrel foraging on spruce beetles. - w/ Troy et al. 3.Nest-type use by red squirrels and the influence of the spruce beetle outbreak. - w/ Patrick Bergeron

Chapter 1 - Red squirrel population dynamics - What controls red squirrel population dynamics? Density regulated Food limited What are the key life-stages in relation to population growth? Age-specific birth rates Age-specific survivorship Significance of study: Observation error ~ 0 Long-term data set with variation in density and food Other studies addressing contribution of life-history stages to population dynamics are ungulates. Further chapters will examine variation of key life stages with respect to territory quality Same population dynamics patterns will be examined later in thesis with individual variation and spatial heterogeneity in food.

Chapter 2 - Local dynamics of cone production by individual trees - Masting occurs over large spatial scales, how synchonous is masting over small scales? Highly synchronous On average, high cone production occurs, but also variation at local scales Significance of study: Masting is defined as a process occurring over large distances, and only 1 study (Bjornstad et al. 2004) looks at smaller scale patterns in acorn production Demonstrating variation in cone production patterns is critical for describing spatial variation in the food resource for further chapters Asynchonous “masting” patterns within a population may allow persistence of a seed predator population

Median cone production patterns

Individual patterns of cone production: (n=160) Actual cones Year

Individual patterns of cone production: (n=160) Residual (from median) Year KL SU

Correlation of cone production Within grid only (n=58 each) Correlate cone production by individual trees - spearman rank Generate 5000 bootstrap resamples to determine mean and se Compare mean correlation coefficient to 1 (and 0.7) (1 = perfect synchrony, 0.7 = acceptable correlation; one sided single sample t-tests)

Correlation of cone production Results: Mean correlation ± se = ± p<0.001 Correlation in cone production KL Mean correlation ± se = ± SU p<0.001

Chapter 3 - Factors influencing cone production by white spruce - Significance of study: Integrate spatial and temporal aspects of cone production by individual trees Use cone production model estimate cone production over the entire study area, and backcast cone estimates for further analyses

White spruce cone production patterns

Model fits: Cone production 2002 Model: GAM - variables: UTMx, UTMy, slope, aspect, basal area, local den, local dbh, UTMx:basal Null deviance: (n=517) 2002 Model df Resid. Dev. Dev. Explained GAM % Fit of model to data: Observed vs. predicted r 2 =.60 Other factors to include: - time lags, - weather conditions

Take Home (so far) Chapters 2 & 3: Cone production by individual white spruce trees is NOT perfectly synchronous Local conditions have a strong influence cone production Spatial variation in resource availability may affect individual performance and the population dynamics of seed predators, even within a local area

Chapter 4 - Determinants of territory size in red squirrels - What determines territory size in red squirrels? Population density Food abundance (cones) Sex of owner Age of owner Reproductive status Significance of study: Long-term data allows multiple combinations of density and food abundance, both have been proposed as determinants of territory size.

Temporal variation in red squirrel territory sizes (June SU A-J 1-10)

Chapter 5 - Resource acquisition, overwinter survival, & reproductive output of red squirrels - Objectives 1. Quantify the spatial distribution of food resources available to individuals in a wild population in a relatively low food year. 2. Compare survival and reproductive success among individuals with quantified resources. 3. Relate food resources available to individuals to those available based on equal resource partitioning. Significance of study: Lomnicki (1980) suggested that the differential ability of individuals to acquire food resources will influence predictions of population persistence. Establishing a link between food availability to individuals in a wild population and is extremely difficult. Will link with later chapter in thesis looking at the level of individual variation needed in population dynamics models.

Individuals survive & reproduce Unequal resource partitioning At low food, unequal resource partitioning can allow population persistence, whereas equal partitioning would lead to the population not persisting Resource partitioning & Population persistence Individual Available Resources Minimum per cap resources required for maintenance

Heterogeneity and Resource Acquisition Hypothesis:  Local resources determine individual survival and reproductive success. Predictions: 1.Individuals will have differential resources available. 2.Individuals with high resources will have higher survivorship and will be more likely to reproduce.

Grid-scale variation in 2002 cone production

Spatial variation in Habitat Quality Food abundance: How does spatial variation affect individuals? 1.Quantify spatial distribution of resources. -Transect sampling for: (~ 10% of study areas)  White spruce density & dbh - Cone production counts

Spatial variation in Territory Quality August Territories visually mapped (n = 27, adults) - Territory size determined: 100% MCP - Territory quality: Total # cone producing capable trees in territory (>5cm dbh) Total #cones = #trees in territory * avg #cones/tree (n=15)

60 m Territory size (ha) - August 2002

60 m Number of white spruce trees (>5cm dbh) in August 2002 territories

m Estimated number of white spruce cones (in 1000’s) in August 2002 territories

Territory Quality & Overwinter Survival Logistic regression (stepwise): Overwinter Survival: (n=27) Survivors = 17, not surviving = 10 Independent variables: - Territory size - # trees on territory - # cones on territory - Territory size ns - # trees on territory sig - # cones on territory sig Percent Correct Predictions: 78% (14 / 17 survivors) ( 7 / 10 not surviving)

Territory Quality & Reproductive Success Logistic regression (stepwise): Female Breeders: (n=11) Produce offspring = 7, no offspring = 4 Independent variables: - Territory size - # cones on territory - Territory size ns - # cones on territory sig Percent Correct Predictions: 82% ( 6 / 7 breeders) ( 3 / 4 nonbreeders)

Fall 2002 Resource Heterogeneity & Equal resource Partitioning – population persistence Fall 2003 n=22 Most  Least # cones on territory

Summary  Even in relatively-low average food conditions, individuals do survive overwinter and reproduce, contingent on local (ie. territory) resources available.  Differential territory quality, thus individual variability, may influence population persistence.  Resource partitioning likely more Influential in low food years.

Other factors to consider  Time-lags. Squirrels cache cones.  Cohort effects, age effects, etc. on survival & reproduction.  Temporal patterns of spatial variation in food availability.

Things I’d like to see done  Continuation of additional cone count data on KL & SU  Collaborative paper on fitness measurements.  Territoriality in food add.