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An outline and study guide for a university ecology lecture covering temperature regulation in animals, including terminology, functional endothermy and ectothermy, and responses to environmental temperature. Additionally, it discusses population dynamics, including methods for estimating population size and growth rates using mark-recapture and life table analysis. From a bio 320 ecology lecture at morehouse college.
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Section II Outline Phenotypic Responses to Temperature Phenotypic Variation Life History Phenomena Populations: Life Table Analysis Population Growth, Exponential Population Growth, Logistic Limits on Population Growth Human Population Growth Limits
Responses to Temperature Upper Limits Most organisms cannot tolerate temperatures greater than 45°C because protein denaturation begins at this and higher temperatures. Exceptions are photosynthetic cyanobacteria which may tolerate 75°C, and some thermophilic bacteria that exist in hot springs at temperatures close to 100°C. Lower Limits Cold tolerance is limited by ice crystal formation. Solutes in water depress the freezing point and inhibit ice formation. Glycerol and glycoproteins may be produced specifically to depress the freezing point of body fluids. Metabolic Response Metabolic rate responds to temperature, as temperature increases, chemical reaction rates increase. Typically, there is a 2x - 4x rate change for each 10°C change. Temperature can influence protein conformation so functional conformation changes with temperature. Temperature Regulation: Terminology Classification Source of Body Heat Endothermy - internal heat source Ectothermy - external heat source Constancy of Body Temperature Homeothermy constant within a range of environmental temperatures Poikilothermy changing with environmental temperature Ectothermy (functional - adaptation definition)
Variation in functional ectotherms: Pseudoendothermy results from active metabolism (muscle activity) Temporal variation in elevated constant body temperature flying insects some snakes (pythons) some fishes (mackerel) Spatial variation within the body, hot core, cold extremities mako sharks tuna flying insects Responses to Environmental Temperature and Temperature Regulation Endothermic body temperature regulation control of insulation muscular heat production evaporative heat loss control of heat exchange by conduction and convection Body temperature and metabolic rate as a function of ambient temperature for typical endotherms. Figure symbols: TNZ = thermal neutral zone (the range of ambient temperatures at which metabolic rate is minimal and the animal is at its basal metabolic rate), LCT = lower critical temperature (the low end of the TNZ), UCT = upper critical temperature (the upper end of the TNZ), LLT = lower lethal temperature (temperature at which lethal hypothermia occurs), ULT = upper lethal temperature (temperature at which lethal hyperthermia occurs). (after Eckert and Randall, 1983, p 723, Fig. 16-28) Outside the ambient temperature range of the TNZ an animal must expend energy to maintain a constant body temperature.
Within the TNZ, constant body temperature is maintained by regulating heat loss: Behavioral control (body orientation and habitat choice) Insulation control Vasoconstriction/dialation At ambient temperatures greater than the upper critical temperature, evaporative cooling becomes important. There is considerable variation among endotherms in the width and limits of the TNZ. In some endotherms, the TNZ is a point rather than a range of temperatures (data from Prosser, 1973). Body Temperature and TNZ Limits Species Body Temperature LCT UCT Homo sapiens 37°C 27°C 32°C Peromyscus 36.4°C 27°C 34.5°C Quail 40.6°C 27.3°C 37.5°C Ptarmigan 39.6°C 4.0°C 36°C Insulation and surface area:volume ratio influence rates of heat loss in endotherms living at relatively cold ambient temperatures. The LCT and the rate of metabolic rate change with decreasing ambient temperature are both a function of heat loss rates. The position of the LCT, and slope of typical low temperature response curves are shown for well insulated and poorly insulated animals. (after Eckert and Randall, 1983, p 727, Fig. 16-32)
Endotherms have accelerated development rates and begin reproduction earlier than ectotherms of the same body size. Age at first reproduction is shown as a function of body mass for ectotherms and endotherms. (Figure from Downhower and Blumer, unpublished) Temporal Responses to Temperature Behavioral and Physiological Responses to environmental conditions or resources Acclimatization: Response to multiple factors (under natural conditions) Acclimation: Response to single factor (under laboratory conditions) Both acclimatization and acclimation (collectively termed acclimation by Ricklefs) involve changes in behavior, structure, physiology, and biochemistry in response to continued prevailing environmental conditions or resources. When environmental temperatures change acclimatization or acclimation can result in a change in metabolic rate responses to temperature. Swimming speed of goldfish changes with ambient temperature, but the position of the swimming speed versus temperature curve is dependent on the temperature at which the fish were living (acclimated) prior to the test (Ricklefs, 1996, p 219, Fig. 10.12, also see p 76, Fig. 3.17).
Acclimation occurs in ectotherms, such as goldfishes, and in endotherms as shown below for ptarmigan. Metabolic rate responses to temperature are different in summer and winter-acclimated willow ptarmigan (Ricklefs, 1993, p 189, Fig. 10.11). Acclimation responses to temperature are also observed among plant species (Ricklefs, 1996, p 220, Fig. 10.14). Acclimatory responses are defined as reversible and therefore plastic, but some responses to environmental conditions or resources are irreversible. Irreversible responses are part of the developmental process in plants and animals.
Ecotypic Variation Ecotypes are local specializations within a species that have evolved as a result of natural selection of subpopulations within a species. Ecotypes are genetically different from each other and reflect an evolved response to local environmental variation. This term was first used to describe variation among plants. In any species, observed variation in size, shape, coloration, behavior, physiology, or biochemistry may be a product of current environmental differences between the sites at which individuals are living, a product of heritable differences genotypic differences = ecotypic differences) between individuals from different sites, or a combination of both causes for phenotypic variation. Transplanting individuals possessing different traits to a constant environment or performing cross transplants between natural sites is a means of evaluating the relative importance of environmental and genetic variation in producing the observed phenotypic variation. The finding of persistent differences between subpopulations independent of environmental conditions suggests that genetic variation underlies observed phenotypic variation. The cause for variation in yarrow ( Achillea ) is evaluated by growing seeds from different subpopulations in a garden near sea level. The persistence of subpopulation differences in growth form, height, and amount of seed production indicates that subpopulation differences are ecotypic (have a genetic basis) (Ricklefs, 1996, p 322, Fig. 14.16).
Clinal Variation Often the geographic variation observed within a species is gradual and continuous (for example biomass and linear body measures). Gradual geographic variation in phenotypes is termed clinal variation. The causes for such variation can be either environmental differences, genotypic differences, or both. The causes for clinal variation and discontinuous variation are evaluated in the same manner. Clinal variation caused by genetic differences (=ecotypic variation) is seen in a species of field cricket in Japan. The duration of nymphal development and adult head width remain different even when cricket nymphs from different environments are raised under constant laboratory conditions (Ricklefs, 1996, p 323, Fig. 14.17). Reproductive Life Cycle Patterns (Variation) Semelparous: single life-time reproduction, “big-bang” life cycle reproduction leads to death of adults because all effort goes to offspring production at one time salmon, bamboo, annual desert plants Iteroparous: repeated reproduction during life-time reproduction does not typically lead to death of adults most mammals and birds
Single Census Methods:
Total number marked in population Total number estimated in population Calculations: € Proportion of Population Marked (PPM) = Number of marked recaptures in sample at t 1 Total number in recapture sample at t 1 € Population Estimate = Total number marked in population released at to PPM Multiple Census, Mark-Recapture Sequential population estimation Assumption of a closed population no longer necessary Total population at time t 1+ n = Total population at t 1 + dilution (gain) - loss Sequential sampling of a given population permits an estimate of survival rates: € Proportion of Individuals Surviving During Time n
Number of marked individuals recaptured at time t1+n Number of marked individuals recaptured at time t 1 Loss Rate = Death + Emigration (per unit time) = 1.0 - Survival Rate Gain Rate = Births + Immigration (per unit time)
Multiple Census Methods:
Life Table Analysis Definitions: x = stage or age interval ax = total number of individuals alive at start of age x lx = proportion of original cohort surviving to the start of age x lx = ax ao mx = proportion of individuals dying between age x and x + (age specific mortality rate) mx =
ax sx = age specific survival rate sx = 1 − mx bx = fecundity at age x (individual fecundity) mean number of offspring (eggs) per surviving adult at age x lxbx = offspring (eggs) per original cohort member at a given age x Fx = total number of offspring (eggs) produced by a cohort at age x Basic Reproductive Rate ( Ro ) is the reproduction per original cohort member. Ro =
ao
Expectation for further life ( ex ) for individuals at age x is the weighted mean of survival through each age interval after age x. The units of ex are the age intervals used in the life table. ex =
lx
i = x ∞
surviving in a given age interval.
Types of Life Tables Cohort Life Table (Horizontal Table): Follows a group (cohort) from birth to death. This is often very difficult and may only be possible retrospectively, by cohort estimation. Methods: 1. Direct observations on survivorship (Ricklefs, 1996, p. 334, Table 15.6)
Life table for Dall mountain sheep based on age at death (cohort estimation).
Types of Life Tables Static Life Table (Vertical Table): Evaluation of all age classes at one point in time, this is a time specific analysis, also called an age structure table. Static life tables are imperfect (they may not correctly indicate the survival probabilities of a given cohort over time) but static life table data is often better than nothing. Assumptions for a static life table to correctly indicate cohort survival probabilities:
