SLE251: Factors Affecting Longevity in Mammals Project Report

This report investigates the relationship between reproduction, development, and longevity in mammals, using data from the PanTHERIA database. The study explores the hypothesis that longer gestation, smaller litter sizes, and larger social group sizes contribute to longer lifespans. Statistical analysis, including correlation and regression models, was performed to assess the impact of variables like litter size, social group size, gestation length, inter-birth interval, and sexual maturity on longevity. The results indicate that reproductive habits, such as frequent mating, negatively impact longevity. The report also discusses the professional context, skills acquired, and job adverts related to the field of mammal biology. While the study found significant relationships between reproductive and developmental processes and aging, the impact of social bonding on longevity was not conclusive for all species. The report concludes by highlighting the importance of understanding these life history trade-offs for conservation and further research.

Running head: MAMMAL LIFE HISTORIES : FACTORS AFFECTING LONGEVITY
SLE251 2019: MAMMAL LIFE HISTORIES: TRADE-OFFS
Name of Student
Name of University
Student ID
Author Note

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 1
Table of Contents
Main Project Report....................................................................................................................2
Introduction.............................................................................................................................2
Methods...................................................................................................................................2
Results.....................................................................................................................................3
Discussion...............................................................................................................................8
References.............................................................................................................................10
Professional Context.................................................................................................................11
Skills acquired.......................................................................................................................11
Job adverts............................................................................................................................12
Science Related Field........................................................................................................12
Non-Science Related Field...............................................................................................13
Addressing selection criteria.................................................................................................14

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 2
Main Project Report
Introduction
This report seeks to study the relationship between the three aspects of life process and
tries to understand if and how longevity in mammals is related to reproduction and
development. It also explores the impact of social bonds that may have on longevity among
190 mammal species.
Lemaître et al.(2015) in their paper discuss how it was seen that in 21 out of 26 studies
exploring the trade off between reproduction, especially during early life and decline in
fitness indicator with age, early life reproduction contributed to a faster decline in fitness with
age. Another study by Mcfarland et al.(2017) studied the life history of female baboons and
discusses how greater social bonds contributed to higher fitness metrics. Keeping in line with
these studies, the report has based its analysis.
The report poses the hypothesis that, “Longer gestation length, smaller litter size and
shorter inter-birth interval, higher sexual maturity age and larger social group size amount to
significantly longer lifespan in mammals”. Following this, a regression model was fit to check
the impact of the significant variables on the longevity.
Methods
Data was obtained from the PanTHERIA database that is available online (Jones et al.
2009). The variables ‘litter size’ (X1), ‘social group size’(X2), ‘gestation length’(X3),
‘inter-birth interval’(X4), , ‘sexual maturity’(X5) and the response variable ‘longevity’(Y).
A total of 190 species were considered who had observations on all the variables being
considered.

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 3
Following a descriptive analysis of the variables, using the five point summary
measures and measure of central tendency and dispersion, a correlation analysis was carried
out to compare the relationships among the variables. Then a linear regression was used to
test for the linear relationships between each predictor and the response variable. The t-test
for significance of regression coefficients was used to check whether the variable had
significant impact on the longevity or not.
The validity of the regression was then followed up with checking for the assumption
of equal variance by comparing the fitted values with the residuals. Two models were fit, as
the first model failed to abide by assumptions of equal variance.
Results
A simple descriptive summary, consisting of the five point summary measure(median,
1st quartile, 3rd quartile, minimum and maximum) as well as the central tendency measure of
mean and variance measures of standard deviation, range and inter-quartile range was done.

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 4
Figure 1: Boxplots of Each Variable
Figure 2: Scatter plots of longevity against litter.size

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 5
Figure 3: Scatter plot of longevity against gestlen
Figure 4: Scatter plot of longevity against social.group.size
Figure 4: Scatter plot of longevity against sexual.maturity

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 6
It was observed that as per Spearman’s rank Correlation, X1 has a moderate negative
correlation, X2 has low but positive correlation and X3. As per both correlation coefficient
measures, X4 and X5 have high positive correlation with Y respectively. The t-tests for
significance of r2 were found to be significant at 5% level for all variables.
Regression Model 1:
The goodness of fit of the model, as indicated by the multiple R2 statistic was found to
be 0.6655 and the adjusted R2 statistic was found to be 0.6564. The residual standard error
was reported as 125.7. X1 and X2 were found to be insignificant at 5% level.
The one-way ANOVA test to check overall significance of the model, indicate that the
regression model is significant, as follows:

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 7
Figure 6: Fitted Longevity values against Residuals for model 1
Regression Model 2:
The goodness of fit of the model, as indicated by the multiple R2 statistic was found to
be 0.6635 and the adjusted R2 statistic was found to be 0.6562. The residual standard error
was reported as 125.7. X1 was found to be insignificant at 5% level.

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 8
The one-way ANOVA test to check overall significance of the model, indicate that the
regression model is significant, as follows:
Figure 7: Residuals vs Fitted Values for model 2
Discussion
Comparing the descriptive measures and box-plots in Figure 1, X1, X2 and X4 were
found to be right skewed indicating that most of the species tend towards the lower end of
the respective distributions. The scatter plot suggests deviation from linearity. Therefore dor
these we consider Spearman rank correlation. X2 and longevity indicate low positive
correlation. This can be validated with findings of many other studies specific to various

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 9
species that higher reproduction may negatively impact fitness and longevity, e.g., Pritchard
et al.(2013) studying survival of dairy cattle and Nussey et al.(2006) studying the early life
aggressive mating habits of the red deer. This is mirrored in the findings here, where X4
show strong positive correlation with longevity. Even X3 which also signify less frequent
mating shows high positive correlation. X5 also shows high positive correlation, which is
also supported by the prior findings of Nussey et al.(2006), in context of the steeper
senescence of red deer owing to their early sexual maturity. The regression model 1 (Table
3), was found to be violating the assumptions of homogeneity of residuals, required for
regression as per Figure 3 (Haddad et al. 2019). Hence the insignificant predictor, X2, was
excluded, following which it was found to adhere to assumption of homoscedasticity or
equal variance and normality of residuals (Figure 4). X1 was found to be insignificant here,
perhaps because model does not adjust for the different species. The model was nonetheless
seen to explain 65.62% of the variation in Y.
The study finds reasonable evidence that longevity is negatively impacted by
aggressive reproduction habits among mammals, and traits that contribute to increasing
lifespan in mammals. Social group associations was not found to have any convincing
impact however it may be arising due to the nature of the study itself and diving into genus
specific groupings could bring more light into the matter.

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 10
References
Haddad, J.N., Rached, Z.S., Jajou, A.F. and Hage, R.M., 2019. On Multiple Regression
Diagnostics. Applied Mathematical Sciences, 13(9), pp.415-421.
Jones, K.E., Bielby, J., Cardillo, M., Fritz, S.A., O'Dell, J., Orme, C.D.L., Safi, K., Sechrest,
W., Boakes, E.H., Carbone, C. and Connolly, C., 2009. PanTHERIA: a species‐level database
of life history, ecology, and geography of extant and recently extinct mammals: Ecological
Archives E090‐184. Ecology, 90(9), pp.2648-2648.
Lemaître, J.F., Berger, V., Bonenfant, C., Douhard, M., Gamelon, M., Plard, F. and Gaillard,
J.M., 2015. Early-late life trade-offs and the evolution of ageing in the wild. Proceedings of
the Royal Society B: Biological Sciences, 282(1806), p.20150209.
McFarland, R., Murphy, D., Lusseau, D., Henzi, S.P., Parker, J.L., Pollet, T.V. and Barrett,
L., 2017. The ‘strength of weak ties’ among female baboons: fitness-related benefits of social
bonds. Animal Behaviour, 126, pp.101-106.
Nussey, D.H., Kruuk, L.E., Donald, A., Fowlie, M. and Clutton‐Brock, T.H., 2006. The rate
of senescence in maternal performance increases with early‐life fecundity in red deer. Ecology
Letters, 9(12), pp.1342-1350.
Pritchard, T., Coffey, M., Mrode, R. and Wall, E., 2013. Understanding the genetics of
survival in dairy cows. Journal of dairy science, 96(5), pp.3296-3309.

MAMMAL LIFE HISTORIES: FACTOR AFFECTING LONGEVITY 11
Professional Context
Skills acquired
This project has challenged me to develop and dive into the domain of mammal
biology and understand various concepts in depth before I could frame my own conjectures
and interpret the meaning of the data.
I was challenged to critically analyse the data and findings in light of the domain
knowledge of mammal life-history.
Furthermore, it was required of me to effectively articulate and present the hypothesis,
the rationale behind the approach taken to validate it and present all of the findings in a
concise and clear manner.