Conservation (last three 3 lecture periods, mostly as a led discussion). We can't cover everything, but that should serve as a rough outline.

Transcription

1 Comments on the rest of the semester: Subjects to be discussed: Temperature relationships. Echolocation. Conservation (last three 3 lecture periods, mostly as a led discussion). Possibly (in order of importance): Biogeography. Predator/prey relationships. Human evolution. We can't cover everything, but that should serve as a rough outline. Temperature relationships. If you look at your text there are lots of other interesting topics, but many of them are covered in other classes: Ecology/behavior/Mating behavior, etc. Yes, mammals will occasionally bring some unique aspects to this, but much of the stuff here is applicable to animals (or even plants) in general. (We are not going through this in nearly as much detail as presented in your text). First some definitions: Endotherm - animal that maintains its body temperature internally (gets heat from metabolic processes). Mammals are considered to be endotherms (so are birds (and dinosaurs, though birds are now thought to be dinosaurs)). Ectotherm - animal that maintains its temperature using external sources: For example, suns itself to warm up, goes into the shade to cool off. Typical examples would be our reptile friends (some sea turtles may be slightly endothermic).

2 Some other definitions that are still very useful: Homeotherm - body temperature stays constant. Again, may mammals are examples, though this isn't always obvious. Temperatures of hibernating mammals are not constant Lizards can have remarkably constant body temperatures. Poikilotherm - body temperature changes. Again, typical examples might be reptiles or amphibians, but only if they're not actively regulating their body temperature. (Text uses heterotherm, but poikilotherm is an older but well established term). (Heterotherm can also have other definitions). Some colloquial terms (which are totally inaccurate) are warm blooded and cold blooded. Some aspects of endothermy: Endothermy is expensive! Endotherms must eat all the time to get enough energy to survive. Endotherms have also evolved a large number of traits to specifically deal with being endothermic. Insulation, sweat glands, etc. (more below). So why be endothermic? Mammals can be active at a much wider range of temperatures than ectotherms. Found in arctic, desert, can be active at night, day, etc. Also have a much higher capability for sustained activity. (E.g. - try catching a lizard. It won't be easy. But if there was no place for the lizard to hide, you would eventually be able to run him down). The above are huge advantages over ectotherms: (You don't see reptiles or amphibians in the arctic). Endothermy is thought to have evolved in the late Triassic, although no one knows for sure.

3 As an aside, ectotherms need to eat much less, don't need insulation, and can simply hibernate when it gets too cold - there are advantages to being ectothermic as well. Text mentions a thermoneutral zone for most mammals: Cold adaptations: This is a range of temperature at which the animal doesn't have to expend much energy to control it's body temperature. Below this zone, animal needs to spend energy to keep warm. E.g., increase metabolism. Above this zone, animal needs to spend energy to cool off. E.g., evaporative cooling. Text very nicely divides this into four different strategies. Large body size: Insulation: This decreases surface to volume ratio, so animal will loose less heat. Bergmann's rule refers to the idea that similar animals will increase in size as one moves to colder climates. A bit controversial, but overall it seems to hold up quite well. Text gives several examples (e.g. lemmings vs. voles, etc.) Another adaptation that should be mentioned is that limbs and extremities are often much smaller in cold-adapted species. Very long legs are absent, ears are more rounded and shorter, etc. Fur can provide excellent insulation. Some mammals obviously shed fur, and thickness will be different for winter/summer. Other adaptations are not so obvious: Polar bears actually have black skin (any leftover light that gets through coat can help keep them warm).

4 In water another frequent insulating material is blubber. Primary insulating material in whales and many seals. (Fur can trap air and even act as an insulating layer). Blood supply to blubber can be restricted to prevent heat loss. Other physiological adaptations: Vasoconstriction - cut off blood supply to surface areas where heat can be lost. Shivering - increases metabolic heat (expensive). Counter-current systems to warm blood coming back from extremities. Hibernation/torpor: Allows extremities to be kept colder than otherwise. (Something similar is actually used by dolphins to cool the testes). Mammals can enter hibernation. Generally we think of this as happening on an annual basis, but some animals may do this almost daily. Text mentions elephant shrews Other small mammals (e.g., rock hyraxes) also lower their metabolism overnight, but not to the same extent. Body temperature drops to near ambient, respiration and metabolism slow down considerably. Animal will often put on a layer of fat to prepare for hibernation. Waking up from hibernation can be very expensive and require sufficient fat (particularly brown fat - details in text). Animals without sufficient fat may not be able to wake themselves from hibernation. (Used to cause problems with cave-hibernating bats). Of course, another way to adapt to cold conditions is simply to leave. Many mammals (incl. bats) will migrate to avoid colder conditions.

5 Heat adaptations. Exercise Several ways to deal with excessive heat. Dissipate heat through vasodilation: This is sort of the opposite to the above. Blood is shunted to the skin or to areas with large surface area so heat can be lost. Use evaporative cooling: Many desert dwelling animals have very large ears with extensive capillaries. Rabbits, elephants, etc. Sweating and panting both evaporate water (as water evaporates, it takes heat with it). Use behavioral means: This is very efficient for temperature control, but can cause serious problems if water is not easily replaced. (Humans have one of the best system of sweat glands of any animal). Other animals can spread saliva on themselves, or even urine to help with heat stress. Don't underestimate this! Animals get into the shade, burrow underground, etc. to get out of the heat. (As an aside, most deserts come alive at dusk - most animals other than humans have enough brains not to be active during the day). Other adaptations: Some animals (camels, oryx) can tolerate increased body temperatures. If animal needs to exert itself (running after prey, or getting away from predator), this can cause extra heat load. This can also affect the behavior of animals: Jackrabbits may try to slink away from predators rather than run full out in an effort to keep cool.

6 Text speculates that this may be the reason cheetahs can't run far. It probably is a contributing factor, but more likely is simply that cheetahs are sprinters, not endurance runners. Text follows this up with sections on: Locomotion efficiency (Seriously doubt, for example, that North American cheetahs were any better at long distances). Discusses how different forms of locomotion affect energy needs, and how this can change with the size of the animal. E. g. running vs. hopping vs. walking, etc. Water regulation: Discusses different strategies for saving water including: Producing extremely concentrated urine (kidneys with more Loops of Henle). Gaining water metabolically. Drinking periodically. Getting water solely from food (e.g., leaves, but in extreme cases even seeds). Feel free to read up on this if you're interested.