Evolution and Ecology for the DAT
/Learn key DAT concepts related to natural selection, evolution, animal behavior, and ecology, plus practice questions and answers
eveyrthing you need to know about evolution and ecology for the dat
Table of Contents
Part 1: Introduction to evolution and ecology
Part 2: Natural selection
a) Requirements
b) In populations
Part 3: Evolution
a) Genetic drift
b) Prezygotic and postzygotic isolation
c) Patterns of evolution
d) Speciation
e) Phylogenetic trees
f) Hardy-Weinberg equilibrium
Part 4: Animal behavior
a) Classical conditioning
b) Operant conditioning
c) Observational learning
Part 5: Ecology
a) Trophic levels
b) Survivorship curves and r/k-selection
c) Ecological succession
Part 6: High-yield terms
Part 7: Questions and answers
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Part 1: Introduction to evolution and ecology
Evolution is a cornerstone of biology, where small changes in the environment can lead to larger changes in a population of animals. Ecology defines the way that organisms interact with each other and their environment. In this guide, we will be reviewing important concepts regarding both evolution and ecology that will be crucial for your success on the DAT. High-yield terms are bolded, and practice questions and answers are found at the end of the guide.
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Part 2: Natural selection
a) Requirements
Evolution is driven by natural selection. Often defined by the phrase "survival of the fittest," natural selection states that individuals possessing traits advantageous for survival and reproduction outcompete those less suited to their environment. This competition leads to an alteration of the population's genetic makeup. Natural selection requires four key conditions:
Variation of traits
Heredity
Overproduction of offspring
Differential survival and reproduction
A requirement for natural selection is that traits are different, and the difference in these traits must lead to a competitive advantage such as increased fitness. Heredity refers to the presence of genetic differences within a population that can be inherited by offspring. An overproduction of offspring leads to a higher demand than supply for necessary resources. As a result of an insufficient supply, competition increases. Differential survival and reproduction mean that individuals with traits better suited to their environment tend to survive longer and reproduce more, passing those advantageous traits to their offspring.
In environments exerting selective pressures—such as food scarcity or predation—individuals with well-adapted characteristics tend to produce more offspring, whose further adaptation enables them to out-reproduce their less-adapted counterparts in subsequent generations. This differential reproduction fosters a progressive increase in allele frequency and its accompanying adaptive traits throughout the population. Shifts in selective pressures prompt a similar evolutionary response, favoring genotypes better equipped to confront the novel challenges.
b) In populations
Populations are groups of individuals of the same species living within a specific geographic area. Understanding populations is crucial for unraveling the dynamics of evolution, ecology, and biodiversity.
Generally, populations boasting greater allele diversity tend to exhibit more successful differential reproduction. Yet, this diversity may fluctuate due to processes like inbreeding and outbreeding. Inbreeding is mating within a population, and it diminishes trait variability and consequently, reproductive success. Conversely, outbreeding occurs when individuals from different populations interbreed. Outbreeding injects fresh genetic variability into a population, bolstering reproductive fitness.
Importantly, selection for traits operates at various levels, encompassing individual and group dynamics. Individuals harboring advantageous traits propagate their lineage, while groups engaging in beneficial behaviors enhance the collective reproductive success. Notably, altruistic behaviors exemplify group selection, wherein individual reproductive success may be compromised, but the overall fitness of the species is enhanced.
Stabilizing selection, one of the modes of natural selection, operates to maintain the fitness of intermediate phenotypes by favoring traits that are well-suited to prevailing environmental conditions. This form of selection acts as a stabilizing force, preserving the status quo within populations. For instance, in a population of tree-dwelling rodents, stabilizing selection may favor individuals with intermediate body sizes, as they strike a balance between agility in navigating branches and energy efficiency.
Directional selection, on the other hand, shifts the distribution of traits within populations towards one extreme, driven by changing environmental pressures. In environments undergoing rapid change, individuals with traits that confer a selective advantage experience increased fitness, leading to the gradual evolution of populations. An example of directional selection is the evolution of longer necks in giraffes, enabling them to reach higher foliage for food resources during periods of drought.
Disruptive selection, the third type of natural selection, favors extreme phenotypes at the expense of intermediate ones, leading to the diversification of traits within populations. This form of selection is often associated with heterogeneous environments where multiple selective pressures exist. For instance, in a population of fish with varying prey preferences, disruptive selection may favor individuals with either large mouths for capturing large prey or small mouths for feeding on small prey, resulting in the coexistence of two distinct phenotypes.
FIGURE 1: TYPES OF NATURAL SELECTION
In summary, fitness serves as the guiding principle for evolution, driving the emergence and persistence of traits within populations. Through the lens of comparative anatomy and the mechanisms of natural selection—stabilizing, directional, and disruptive—we gain deeper insights into the intricate interplay between organisms and their environments, illuminating the pathways of evolutionary change within populations.
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Part 3: Evolution
a) Genetic drift
Genetic drift is a pivotal mechanism that drives changes in allele frequencies, particularly when populations encounter negligible selective pressures. In the absence of selective forces, chance mutations introduce new alleles, shaping allele frequencies across successive generations.
These mutations may yield detrimental effects that diminish an individual's genetic fitness and potentially compromise survival. Notably, inborn errors of metabolism exemplify such deleterious mutations, disrupting vital enzyme production and necessitating specialized diets for affected individuals. Conversely, mutations can also lead to advantageous adaptations, enhancing an individual's genetic fitness. Specialized phenotypic traits, like a bird's beak adaptation for seed retrieval, exemplify beneficial mutations that enable species to exploit unique ecological niches.
Additionally, genetic leakage introduces new mutations. In genetic leakage, genes are exchanged between species, either through inter-species breeding or the incorporation of intracellular genetic material, such as mitochondrial DNA, into the recipient species' genome.
While chance events may lead to the elimination of new alleles, others persist and become fixed within the population. Fixation occurs when a trait's incidence increases within a population, ultimately becoming a prevalent phenotype. Unlike natural selection, where the fate of novel alleles hinges on their selective advantages, genetic drift's influence is more indiscriminate.
Genetic drift's impact amplifies during significant population changes. Catastrophic events, like bottleneck effects, indiscriminately prune variant alleles. The pruning of these alleles leads to decreased genetic diversity among survivors. Similarly, the founder effect, observed in small populations establishing new colonies, further diminishes allelic diversity. As a result of the founder’s effect, new populations are susceptible to additional allele loss via genetic drift. Thus, maintaining high genetic diversity within populations is pivotal to counteracting the deleterious effects of genetic drift.
FIGURE 2: BOTTLENECK AND FOUNDER’S EFFECTS
These evolutionary pressures can culminate in speciation, where a new species is created. This creates two genetically distinct lineages incapable of interbreeding to produce fertile offspring.
The molecular clock theory offers a theoretical framework for estimating species' evolutionary age based on allele frequency changes. The degree of genetic divergence between species correlates with the time elapsed since their evolutionary divergence.
Microevolution and macroevolution represent different scales of evolutionary change. Microevolution refers to small-scale changes within a population over a short period, such as changes in allele frequencies due to natural selection, genetic drift, mutation, and gene flow. An example of microevolution is the development of antibiotic resistance in bacteria. Macroevolution, on the other hand, involves larger-scale changes that occur over long periods, leading to the emergence of new species and higher taxonomic groups. An example of macroevolution is the evolution of mammals from reptilian ancestors.
b) Prezygotic and postzygotic isolation
Prezygotic isolation and postzygotic isolation are mechanisms that prevent species from interbreeding. Prezygotic isolation occurs before fertilization and includes these mechanisms:
Temporal isolation, where species breed at different times or during different seasons
Behavioral isolation, where differences in mating behaviors prevent interbreeding
Mechanical isolation, where differences in reproductive structures prevent successful mating
Spatial isolation, where species’ habitats do not overlap
Gametic isolation, where species’ gametes are not fertile when combined
An example of prezygotic isolation is the different mating calls of closely related frog species that prevent them from interbreeding.
Postzygotic isolation occurs after fertilization and includes mechanisms that reduce the viability or reproductive capacity of hybrid offspring. This can include
Hybrid inviability, where the offspring do not develop properly
Hybrid sterility, where the offspring are sterile, like a mule (a hybrid of a horse and a donkey)
Hybrid breakdown, where the first-generation hybrids are viable and fertile, but their offspring are inviable or sterile
An example of postzygotic isolation is the sterility of ligers, a hybrid between lions and tigers.
c) Patterns of evolution
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