Ecology Lecture Notes

Chapter 7, Natural Selection in Ecological Settings

1. Spatially varying natural selection
1. Clines - a gradient in gene frequencies or phenotype frequencies within a population due to environmental variations over a large geographical area
2. Causes:
1. not always known
2. Industrial melanism in the moth Biston betularia in Great Britain during beginning of industrial revolution (see p. 142, fig. 7-1)
2. Temporally varying natural selection - Variation of selective pressures with regard to periods of time; selective pressures may change over time, therefore changing the genotype and phenotype frequencies with in a population from one generation to the next
3. Density-dependent natural selection - also called K-selection; occurs in crowded conditions such as in populations of slow growing, late-flowering plants where differently-aged individuals may coexist; the overall growth rate of the population is relatively constant and is usually represented by "K", hence the name K-selection.
4. Density-independent natural selection - also called r-selection; occurs in dispersed populations of rapid-growing, early-flowering plants where individuals are of roughly the same age; the overall growth rate of the population is variable depending upon the time of the year for spp. that complete their growing cycle in less than one year and new populations of subsequent generations do not coexist with older ones; because the growth rate (r) is the determining factor, r-selection is sometimes used to refer to density-independent natural selection.

Chapter 8, Social Behavior in Animals: Community Behavioral Interactions within Groups of Birds, Mammals, and Insects

1. weaver finches: differences in social behavior are seen when differences in predation, resource utilization, and resource availability occur among various interacting populations of weaver finches; in savanna habitats, colonial nesting, feeding-in-flocks, and polygamy are more common than in evergreen forest habitats where territoriality, solitary feeding, solitary nesting, and monogamy are common.
2. ground squirrels: spp. in eastern N.A. are basically asocial whereas other spp. in different habitats are colonial and very social.
3. bees and ants: extremely variable yet high level of social order, ranging from solitary to eusocial (truly social) - see flow chart on p. 177.

The Ecology of Sex, Chapter 9, p. 182

1. Syngamy - the fusion of gametes; fertilization
1. In animals, syngamy usually requires the physical interaction of mating males and females.
2. In seed plants, syngamy requires a mechanism for transferring pollen from floral structures within or between individuals (self-pollination vs. cross pollination respectively) usually gravity, wind, or animals.
3. In spore-forming plants such as ferns, horsetails, and mosses; syngamy requires mechanisms for fusion of egg and sperm, usually water.
2. Parental investments -
1. the resources that individuals devote to each offspring;
1. these investments can be used to produce:
1. lots of offspring, each receiving relatively small proportions of the resources, or
2. few offspring, with each getting a larger proportion of the investments
2. Males usually produce small gametes which contribute only the genetic information; usually make less of an investment than do females from the point of view of a gamete.
3. Females produce larger gametes containing not only genetic information but also food reserves for the developing embryo and often provide a larger proportion of parental care after birth of the young.
2. Considerations regarding sexual reproduction:
1. Why is reproduction in most organisms sexual?
2. What environmental factors encourage sexual reproduction?
3. Why are there, seemingly, more advantages to asexual reproduction vs. sexual reproduction?
3. Asexual vs. sexual reproduction:
1. Advantages of asexual reproduction - asexual requires no fusion of gametes, or in some plants, self-pollination with out any cross-pollination may occur and result in essentially asexual populations in some spp.; many weeds are asexual and are very well adapted for colonizing new or disturbed habitats both asexually and sexually; asexually by vegetative propagation or cloning of an individual plant; cloning - making multiple copies of genetically identical individuals; examples:
1. dandelion - in populations where self-pollination is predominant, the individuals are very similar, genetically to each other; essentially an asexual population with little genetic variability.
2. certain spp. of weedy, annual plants with short life cycles; many members of the mustard family (Brassicaceae) tend to be rather variable with regard to pollination modes:
1. Leavenworthia sp. - usually a cross-pollinated sp.; however, in the absence of a suitable pollinator, this plant will form asexual populations by self-pollinating; referred to as a facultatively self-pollinated sp.; type of pollination is dependent on environmental factors.
2. Brassica rapa, rape seed - is an obligate cross-pollinating sp.; very rarely self-pollinates, when it does, only a few viable seeds are produced; therefore, any asexual reproduction will have to occur by vegetative propagation.
3. Arabidopsis thaliana - is a facultatively cross-pollinated sp.; usually self-pollinated but can be cross pollinated with relatively little difficulty.
2. Other advantages of asexual reproduction:
1. quick colonization of habitats
2. efficient use of maternal material - the egg; if many obligately sexually reproducing eggs are produced, the maternal investments may, and usually are wasted if a suitable mate is not found; this is referred to as the cost of meiosis - in order for sexual reproduction to occur, haploid gametes must be produced; in most females, not all of the eggs are fertilized and maternal investments are wasted
3. overall fewer parental investments
3. Advantages of sexual reproduction - advantageous in a changing and unpredictable environment due to increase in genetic variablity in offspring; types of advantageous sexual reproduction modes:
1. Facultatively sexual organisms - can reproduce either sexually or asexually; e.g. protozoa and certain invertebrates such as rotifers and aphids; reproduce asexually during summer, and only at the end of the season do they reproduce sexually, thus providing genetic variability during the next, possibly different summer season; they take advantage of good growing seasons by quickly reproducing asexually, and then reproducing sexually during poor growing seasons, producing dormant, sexually drived individuals.
2. Obligately sexual organisms - greater genetic variability, varied offspring out compete asexual clones in nearly all microhabitats except those few where genetic clones are highly adapted, competition between predator-prey relationships within sexual spp. keep sexualality going as well (e.g. predators learn to attack a genetically uniform population of prey and possibly eliminate the prey; only by continually changing genotypes, can the prey survive, thus forcing the predators to be sexual as well); the same is true for pathogenic microorganisms - refer back to the increase in genetic variabilty and antibiotic resistance in spp. that undergo a special form of a, somewhat sexual type of reproduction called conjugation.

Chapter 10, Mating Systems, p. 212

Definition - a mating system is defined as the pattern of matings within a population, including:

1. how mates find one another through mate selection and competition for mates
2. how many different mates each individual has (polygamy vs. monogamy)
3. how long mates remain associated

1. Investments in sexual reproduction:
   Females produce larger gametes, therefore, have more at stake in each mating than males do.
   Usually the female provides most of the post-birth care and invest mores resource into sexual reproduction
   Males produce smaller gametes, therefore, have less at stake
   Usually the male provides relatively little in terms of post-birth care of offspring and, overall, invest less in sexual reproduction
   Females are more discriminating while males are less discriminating
   Eventually the male will likely find an optimum female with which to contribute significantly to the gene pool
   Females are referred to as the limiting gender while males are referred to as the limted gender due to the fewer number of eggs produced.
2. Mating Systems in bird populations: Mostly monogamous - one individual mates with only one partner each breeding season; rare in most animal systems, but more than 90% of all bird spp. are monogamous. Polygamy - one individual mates with two or more partners each breeding season.

Parental Care of Young (Parental Investments): In birds, both males and females provide relatively equal amounts of post-birth resources for offspring, in contrast to other animal systems, especially mammals, where females, usually, provide the greater amount of resources.

Nesting and Care of Young: Precocial - e.g. quail and ducks are covered with down when hatched and can run or swim as soon as their down dries. Altricial - e.g. meadow larks are naked and helpless at birth and remain in the nest for a week or more; require more care after hatching.