Populations Flashcards
Ecology
Scientific distribution and abundance of organisms and interactions that determine these and biodiversity => individual, population, community
Ecological niche
Sum of total adaptations of an organismic unit
Niche
Role of an organisms in its community (not out competed). Includes: foraging strategies, diet, reproductive strategies, social organisation, predators, environment tolerances, morphology, sense adaptations, physiology, competition
Life zones depend on
Humidity and ppt
Charles Elton 1927
A niche is a place in an environment, with relations to food and enemies
Cause 1934
Competition, 2 similar species scarcely occupy similar niches - certain peculiar types of food etc.
Competitive exclusion principle
Complete competitors cannot exists
Niche segeration
Higher species richness = higher efficiency of conservation costs
Hutchinson’s model fall backs:
Not all niches environmental, some behavioural
Not all axes linear
Different species can hold similar niches - same species different niches
Once a niche is vacant, other organisms can fill the position
Fundamental niche
Entire set of conditions under which a species can survive and reproduce => larger
Realised niche
Set of conditions actually used by species after interactions with other species are taken into account => different locations
Specialist niches
Smaller niches than generalists
Levin’s measure of niche breath
B = 1/ total (pi^2)
Pi = probability of individuals that use resource i or probability of diet consisting of i
Niche breath is important so that there is no niche overlap
There is a constant niche breadth
But we do not know how many individuals are in the niche
Niche overlap
Coexistence, including overlapping => hyperspace, reciprocal overlap, asymmetric overlap (pushed out original niche), non-overlapping: abutting, disjunct
Classification of non-overlapping niches
Resource limiting => competition currently occurring, abutting niches indirect indication => niche divergence (competition)
Niche partitioning
Narrow niche - coexists with other species -> more specific. Wide niche - single species on island
Competitive release
Take out one species, another may expand its niche
Explanations for different niches
Competition, evolutionary competition avoidance, (Connell 1980 ‘ghost of competition past’ - competition most = red - breeding success, natural selection eliminates niches more distinct from completion spectrum), evolution in response to natural selection - independent
Population
A group of interbreeding individuals in a given area at a given time
Number of individuals, population density/area, BR + DR id randomly distributed, or mobile = single density. Not all individuals in the population are the same => structured population (age or stage-structured)
Individual
Unitary species - zygote (sexual reproduction) => eugenically unique organism
Modular - zygote => similar modules - expand, new individual
Genet
Individual from SR
Ramet
Module reproduces AS by genet (same genotype)
Population distribution
Spatial location of individual - stationary (sessile) or vary (migration). If movement between groups of individuals is less frequent = local populations
Metrapopulations
Sub-populations linked by dispersal, groups of populations connect by immigration an emigration => larger regional population. Key premises: local breeding and migration
Life tables
Summarise/infer patterns or B and D => overtime follows cohort and record structure at some point in time
Age-sructrured census
Census at single point in time. Multiple can reveal important events over time=> infer multiple cohort dynamics.
Nt+1 =
Nt + Br - Dr + It - Et
Nt = number of individuals at time t, Br/DR between time t and t+1
It = number individuals immigrating t - t+1
Et = number individuals emigrating t - t+1
Why do we estimate populations
To manage ans conserve species and understand BR/DR
Total individual counts, or sampling methods, estimate relative density e.g. facial pellets
Model of populations, N(t) =
N(o) x e^rt
r = intrinsic rate of geometric population increase
Population regulation - dN/dt
Stabilises populations and stops exponential growth
dN/dt = r (1 - N/k) v
K = population carrying capacity (max)
N = population size
Higher N = closer to k
N is small => dN/dt = rN (exponential growth)
N = k/2 => growth rate is highest
dN/dt very small = population size levels off
dN/dt neg => population declines to k
Interspecific reactions: Competition
-/- use same resources and insufficient to supply the combination of needs
Interspecific reactions: Predation
+/- one organism consumes all or part of another, also herbivory and cannibalism
Interspecific reactions: Paratism
+/- Close association with hosts - feed on (don’t always kill) => micro parasites multiply within host survive, macrparasites grown in/on host, don’t multiply
Interspecific reactions: Amensalism
-/0 e.g. large mammals 0, plants near waterhole -
Interspecific reactions: Comensalism
+/0 e.g. egret cattle capture more insects when with large animals - egret +, buffalo 0
Interspecific reactions: Mutualism
+/+ both individuals benefit => facultative pollinations, seed dispersal, permanently paired, at least 1 cannot live independently (obligate)
Predation and population change
Predator/prey cycles e.g. low red = inc in prey = inc in red = dec in prey = dec in pred
Gross primary productivity
Rate energy is incorporated into bodies of photosynthetic organisms (5% solar energy)
Gross primary production
Amount of accumulated energy (metabolic, growth, reproduction)
Net primary production
Energy available to primary consumers
How does temperate and moisture affect biomass?
Warm air = more evaporation and transportation rates
Low temps = low photosynthesis and low production
NPP at equator = high m ++ = high NPP
Decrease in ppt and temp = decrease in biomass
Trophic levels
Divided on how energy is obtained
Assimilation efficiency
Assimilation: ingestion (I) => A + Expelled
Production efficiency
Production: assimilation A => respiratory + P
Detritivores
Eat dead and water
Omnivores
pp and another trophic level
Energy available to given trophic level
Productivity of next lower level (n-1)
Consumption efficiency
Ingestion: production (ln/Pn-1)
Food chain
Sequence of interaction => feeding - short, energetic
Food web
Interconnected food chains. Apex predator - no predators itself
Keystone species
Strong influence on ecosystem but low abundance
Trophic cascade
Change in species community at 1 trophic level affects species community at trophic level not directly above or below e.g. predators reduce herbivores = increase in plant biomass
Community importance for a species, Clx
Species lost during the removal of species X
= ((tN - td)/tN)/Px
tN = quantitative measure of community trait in intact community
td = quantitative measure of community trait after species x removed
px = proportional abundance of species x before removal
Community stability
Equilibrium model
Most natural comms on a continue stable => unstable
Measured as time to recovery from disturbance or variability of comm over time
Stable community
Many interactions (competition and predation), processes operate in a density dependent manner to regulate population sizes, species saturation rare, catastrophic environmental events
Local stability
Environmental changes, communities replaced
Global stability
Maintains itself
Food web generalisations
More species = more linkages, chain lengths short, proportion of species at each level approx constant, omnivory common
How can you study food webs using stable isotopes?
Ratio of isotopes expressed as theta values (parts per 1000). On average thetaN increases by 3.4% in animals relative to their diet => separate animals from different trophic levels. Bioaccumulation.
