BIOGEOGRAPHY, PALEOECOLOGY, AND HUMAN ORIGINS

BASIC BACKGROUND CONCEPTS IN ECOLOGY AND EVOLUTION:

Here’s an effort to summarize basic premises of ecology and evolution that we’ll touched on in the first ‘section’ of the class in exploration of island biology. You should be comfortable with these – i.e., not just know these simple (some simplistic) definitions, but be able to think about these things in context and with background implied (for example, something invoking alleles or heritability implies understanding of basic cell division types and Mendelian genetics...).

I. Basic ECOLOGICAL Processes and Concepts

       A. Populations: (more-or-less spatially defined interacting groups of individuals of same species)

               1. Population growth is potentially exponential, but will be limited by

               2. availability of A (usually one primary) limiting resource particular to situation (= 'density-dependent' regulation), OR

               3. by extrinsic environmental factors that prevent population from reaching carrying capacity (= 'density independent' reg.).

       B. The range of resources/conditions that can support a species, and the range of environmental circumstances that it can tolerate define its fundamental niche (a genetically defined attribute of a population/species; different populations, if genetically divergent, may vary in fundamental niche).

       C. Species with overlapping fundamental niches may compete (i.e., one or both will exhibit reduced population growth rate due to effects on birth or death rate). IF both occupy same area and are resource limited; one or other will, in any given scenario prove the superior competitor, potentially displacing the other from particular habitat (competitive exclusion).

       D. The range of resources effectively used, environments occupied in presence of competitors is a species’ realized niche (which can vary with situation, combination of competitors present).

       E. Species limited by the same resources can’t generally coexist indefinitely (= competitive exclusion principle), but external factors -- e.g., environmental disturbances -- may limit population growth and slow or prevent competitive exclusion.

       F. Diversity – the variety of species co-occurring at a time and place – is, therefore, a function of: diversity of habitat (determines number of complementary niches possible); magnitude of resource basis (even if appropriate conditions for a species, it must ‘control’ enough resources to maintain a viable population); and history (additions of species by immigration and speciation; extinctions due to historical events).

II. Basic EVOLUTIONARY Processes and Concepts

       GENETICS: Look up these terms/concepts and review if you're not comfortable with them: gene, chromosome, karyotype, genome, mitosis, meiosis, dominant/recessive, mutation, haploid/diploid/polyploid, gamete

       A. Evolutionary Fitness: Reproductive success of an individual or genotype compared to others in same population; fitness can only be defined relative to other individuals within same population and is not a population or species property. (Single most important thing to understand!!!!).  

       B. Adaptation: A trait (heritable or not, but subjec to natural selection ONLY if heritable) that contributes to an individual’s ability to cope with its environment (i.e., enhances fitness through increased ability to cope with environment; this is not the ONLY way fitness can be enhanced...).

       C. Natural Selection: Changes in relative abundance (frequency) of heritable traits (or of alleles) within a population over generational time as a consequence of differences in fitness (usually due to superior adaptedness to environment OR to increased mating success (=Sexual Selection)).

       D. Non-selective Evolution: Changes in relative abundance of traits/alleles for other reasons (usually chance effects of small population size or 'sampling errors' during dispersal and establishment of new populations. This includes things like genetic drift, founder effect. Inbreeding (often, but not always, a result of small population size) can enhance these processes by decreasing effective population size. Unbalanced immigration or emigration = gene flow, and can also lead to evolutionary change in a population.

       E. ANY CHANGE in relative frequency/proportion of alleles in a population/species, for whatever reason, constitutes evolutionary change.

       F. Species: A more-or-less isolated/distinct gene pool; a group of organisms (one or many populations) which, in normal course of events, won't (or can't) experience genetic exchange (gene flow). Species concept usually also invokes notion of ecological or adaptive differences. Reproductive isolation between species usually implies a reproductive isolating mechanism (RIM) beyond simple spatial isolation.

       F2. BUT species can include genetically (even ecologically) different, spatially isolated populations (sub-species, races, ecotypes), AND there can be measurable exchange of genes between species that are accepted as distinct (introgression). Species concept becomes ambiguous and not that useful in asexual lineages.

       G. Speciation: Splitting of a species into two; divergence of populations within a species to the point that they’re no longer considered potentially a single gene pool, usually in spatial isolation from one another (allopatric), but sometimes without spatial separation (sympatric or parapatric).

       H. Sibling (sister) Species: Two species resulting from a single speciation event (usually relatively recent); closest living relatives to each other.

       I. Clade: A branch of an evolutionary tree; all the descendants of a particular species existing at some point in history; may include one or many species. A group of species including all member species of any particular clade is defined as monophyletic. (A group including members of more than one clade is paraphyletic or polyphyletic) In principle, all taxonomic groups (genera, families, orders, classes, phyla, kingdoms) should be monophyletic - a single, complete clade.