CHAPTER 9: POPULATIONS & COMMUNITIES (NOTES) (1)STUDYING POPULATIONS -Population: group of individuals of a species who live in an established area together; ex. Gulf of St. Lawrence beluga population; these individuals are subjected to the same conditions (resources, climate, pollution, etc.); mating occurs within a population since its easy for individuals to meet. -Population is described by: 1.Size, 2.Density 3.Distribution

1.1 POPULATION SIZE: Is affected by: (1)Births (2) Deaths (3) Immigration whereby individuals come in from other populations (4) Emigration whereby individuals leave the population -Births and immigration are “positive” factors than increase population size whereas deaths and emigration are “negative” factors that decrease size. -To find out the status of a population, one must consider that positive and negative factors. -A stable population is one that has not changed.

-METHODS FOR MEASURING THE SIZE OF A POPULATION: 3 methods: 1. Counting individuals: useful for small populations like water lilies in a pond. Aerial photos can be used, individuals from snapshots are counted and added to obtain population size. 2. Counting by sample area: useful for larger populations where individuals are either static, slow-moving or not affected by human presence. Individuals are counted in a smaller random sample area (quadrant) and total population is calculated using proportions.

3.Mark and recapture: useful for larger populations where individuals are constantly moving (ex. birds, fish), or are found in vast territories (ex. caribou, marine mammals); steps: 1. Cages or nets are installed; 2. Counting & marking captured individuals 3. Releasing marked an. so they reintegrate their pop.; 4. Cages or nets are installed again; 5. Captured individuals are counted & marked, recaptured individuals are counted separately; 6. Size of population is estimated through a formula.

For example: 100 Canada geese have been captured, marked, & released; on the 2nd capture 200 are caught but 50 are tagged then: pop. size = 100 x 200 = 400 individuals 50

A yellow warbler with a tiny ankle ring tag.

1.2 POPULATION DENSITY - the no. of indiv. within a specific area; ex. 100 raccoons per km 2 in the city versus 5-10 raccoons per km 2 in the wild; varies depending on food available, climate, no. of predators, diseases, etc; can be mathematically calculated:

1.3 POPULATION DISTRIBUTION -the manner in which individuals are spread within a space. There are three types: 1.Clumped distribution (a - right): individuals are in groups; most common type; can offer protection & make food finding easier; ex. fish, wolves, lions 2.Uniform distribution (b): individuals are equally spread so each can obtain a set amount of space & resources; ex. northern gannet 3.Random distribution (c): unpredictable distribution; rare in nature; ex. field bushes

1.4 ECOLOGICAL FACTORS -components of a habitat that affect indiv within a population; 2 types: (1) Abiotic factors: nonliving; chemical (ex. pH, presence of heavy metals, etc) & physical (ex. shallowness of water, sunlight, elevation, humidity, etc) components of the indiv.’s enviro. (2) Biotic factors: living; actions of living players within an enviro.; ex. amount of predators or food present, human activity, death rate, etc -LIMITING FACTOR: -a factor which is affecting the development of a population more so than other factors; ex. in the Arctic the limiting factor for polar bears may be global warming which is causing melting & unavailability of ice floes; -a limiting factor can be detrimental when absent (ex. a house plant placed in complete darkness), found in small quantities (ex. food that is scarce) or found in excessive quantities (ex. an overwatered house plant develops fungus)

1.5 BIOLOGICAL CYCLES IN POPULATIONS - populations normally continually & repeatedly increase & decrease forming an often predictable pattern; ex. prey/predator, snowshoe hare & Canadian lynx, populations are narrowly linked & cyclically fluctuate together;

In Australia, the koala bear and the eucalyptus tree are also part of a biological cycle. These cycles occur when there is exclusivity or near exclusivity, i.e., the lynx’s diet is almost exclusively snowshoe hare & the koala diet is mostly made up of eucalyptus

(2) STUDYING COMMUNITIES - COMMUNITY: a group of species sharing a habitat. When studying a species, the whole community is usually studied as well since species interact and are affected by one another in a community.

2.1 BIODIVERSITY -Biodiversity refers to the amount of different varieties that exist in a community -Biodiversity richness is considered a desirable and positive feature in a community since it is often linked to the resilience of a community – the more species there are, the more variety there is and the less susceptible to diseases and stresses a community will be since different species react differently to negative stresses. -Climate change is causing increasing biodiversity loss in nature, as is many of our agriculture choices (ex. the common banana, Musa paradisiacal sapientum versus other bananas) -We look at two factors when evaluating the biodiversity of a community: (1) Species richness: is the amount of different species within a community. (2) No. of individuals of each species

Fig.9.16 (p.304), community 1 & 2 have the small spp. but community 1 has a greater abundance of these spp. so it is the one with the greatest biodiversity

2.2 INTERACTION BETWEEN INDIVIDUALS IN A COMMUNITY - Species within a community establish one of several relationships: competition, predation, mutualism and commensalism -COMPETITION: a relationship where two entities (individuals or species) compete for the same resources; this relationship is detrimental to both entities involved. There are two types: 1.Intraspecific competition: within indiv. of the same spp.; ex. 2 males trying to woo the same female 2. Interspecific competition: within indiv. of different spp.; ex. a maple & an oak sapling both competing for water in an area PREDATION: relationship where one individual is harmed (eaten – the prey) by the other (the predator) e.g. lion and antelope; this relationship benefits the predator and is a detriment to the prey. PARASITISM: is a type of predation where the predator (parasite) lives in or on its prey (called a host), the parasite feeds on the host, weakening it and sometimes killing the host; ex. AIDS virus and humans, tapeworms and humans, caterpillar eating a leaf.

MUTUALISM: relationship where 2 spp. interact & both benefit from their interaction; this relationship benefits both parties; ex. a sea anemone purposely fits its stalk over a hermit crab protecting the crab with its specialized stinging cells, while the hermit crab leaves some of its food to the sea anemone when it feeds; image right.

COMMENSALISM: relationship where one species benefits and the other is indifferent e.g. the Great burdock (right) surrounds its seeds with burs that stick to the fur of animals (or clothing of humans) coming in contact thus effectively dispersing its seeds, this causes no harm (although possibly causes some annoyance).