Do ectotherms exhibit a shortened life expectancy as they grow faster with higher temperatures? [Alan]
The TSR (Temperature- Size Rule) indicates that ectotherms tend to develop faster at higher temperatures, but mature with smaller body size – though there are exceptions in which animals produce larger bodies. The significance is that egg production is generally a function of body size, so smaller mature ectotherms will likely produce fewer offspring somewhat countering the rapid development rate in terms of the population number effect.
This relationship is not universal since for some ectotherms, the adults are actually larger.
Some arthropods exhibit one generation per year (univoltine species) while others have several generations (multivoltine). The expectation is that the latter insects especially, will likely exhibit more generations – both because the growing season is extended, and the temperature is hotter. The generation time probably will reduce as they mature faster and produce offspring sooner. It is also quite possible that the univoltine species (unless strongly controlled by photoperiod – the length of the day-night time periods) may start to exhibit multivoltine behavior.
Interestingly, the response of ectotherms to temperature change is dependent on the temperature fluctuation to which they are normally adapted. Because daily and seasonal temperature fluctuations in the tropics are generally minimal while those in higher latitudes are often vast, tropical organisms are much more sensitive to global warming than those from higher latitudes.